Merge pull request #19342 from vespa-engine/mpolden/vespa-log

Implement vespa log command

46 files changed, 510 insertions, 114 deletions

diff --git a/client/go/build/build.go b/client/go/build/build.go
index a51518dbb8f..a8342a9fb1e 100644
--- a/client/go/build/build.go
+++ b/client/go/build/build.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package build
 
 var Version string = "0.0.0-devel" // Overriden by linker flag as part of build
diff --git a/client/go/cmd/api_key.go b/client/go/cmd/api_key.go
index b3284daa993..ba2df8c40dc 100644
--- a/client/go/cmd/api_key.go
+++ b/client/go/cmd/api_key.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // vespa api-key command
 // Author: mpolden
 package cmd
diff --git a/client/go/cmd/api_key_test.go b/client/go/cmd/api_key_test.go
index 1deb628c21e..b08758ae21d 100644
--- a/client/go/cmd/api_key_test.go
+++ b/client/go/cmd/api_key_test.go
@@ -17,7 +17,7 @@ func TestAPIKey(t *testing.T) {
 	out, _ := execute(command{args: []string{"api-key", "-a", "t1.a1.i1"}, homeDir: homeDir}, t, nil)
 	assert.Contains(t, out, "Success: API private key written to "+keyFile+"\n")
 
-	out, _ = execute(command{args: []string{"api-key", "-a", "t1.a1.i1"}, homeDir: homeDir}, t, nil)
-	assert.Contains(t, out, "Error: File "+keyFile+" already exists\nHint: Use -f to overwrite it\n")
+	out, outErr := execute(command{args: []string{"api-key", "-a", "t1.a1.i1"}, homeDir: homeDir}, t, nil)
+	assert.Contains(t, outErr, "Error: File "+keyFile+" already exists\nHint: Use -f to overwrite it\n")
 	assert.Contains(t, out, "This is your public key")
 }
diff --git a/client/go/cmd/cert.go b/client/go/cmd/cert.go
index 54a2c09256f..eaf3fc564dd 100644
--- a/client/go/cmd/cert.go
+++ b/client/go/cmd/cert.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // vespa cert command
 // Author: mpolden
 package cmd
diff --git a/client/go/cmd/cert_test.go b/client/go/cmd/cert_test.go
index cd5f88764b9..96b626b5c98 100644
--- a/client/go/cmd/cert_test.go
+++ b/client/go/cmd/cert_test.go
@@ -28,8 +28,8 @@ func TestCert(t *testing.T) {
 
 	assert.Equal(t, fmt.Sprintf("Success: Certificate written to %s\nSuccess: Certificate written to %s\nSuccess: Private key written to %s\n", pkgCertificate, certificate, privateKey), out)
 
-	out, _ = execute(command{args: []string{"cert", "-a", "t1.a1.i1", pkgDir}, homeDir: homeDir}, t, nil)
-	assert.Contains(t, out, fmt.Sprintf("Error: Application package %s already contains a certificate", appDir))
+	_, outErr := execute(command{args: []string{"cert", "-a", "t1.a1.i1", pkgDir}, homeDir: homeDir}, t, nil)
+	assert.Contains(t, outErr, fmt.Sprintf("Error: Application package %s already contains a certificate", appDir))
 }
 
 func TestCertCompressedPackage(t *testing.T) {
@@ -41,13 +41,13 @@ func TestCertCompressedPackage(t *testing.T) {
 	_, err = os.Create(zipFile)
 	assert.Nil(t, err)
 
-	out, _ := execute(command{args: []string{"cert", "-a", "t1.a1.i1", pkgDir}, homeDir: homeDir}, t, nil)
-	assert.Contains(t, out, "Error: Cannot add certificate to compressed application package")
+	_, outErr := execute(command{args: []string{"cert", "-a", "t1.a1.i1", pkgDir}, homeDir: homeDir}, t, nil)
+	assert.Contains(t, outErr, "Error: Cannot add certificate to compressed application package")
 
 	err = os.Remove(zipFile)
 	assert.Nil(t, err)
 
-	out, _ = execute(command{args: []string{"cert", "-f", "-a", "t1.a1.i1", pkgDir}, homeDir: homeDir}, t, nil)
+	out, _ := execute(command{args: []string{"cert", "-f", "-a", "t1.a1.i1", pkgDir}, homeDir: homeDir}, t, nil)
 	assert.Contains(t, out, "Success: Certificate written to")
 	assert.Contains(t, out, "Success: Private key written to")
 }
diff --git a/client/go/cmd/clone.go b/client/go/cmd/clone.go
index 508ad49438f..9bae300c399 100644
--- a/client/go/cmd/clone.go
+++ b/client/go/cmd/clone.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // vespa clone command
 // author: bratseth
 
diff --git a/client/go/cmd/clone_list.go b/client/go/cmd/clone_list.go
index f0ded5385cb..cb8e1acf4e9 100644
--- a/client/go/cmd/clone_list.go
+++ b/client/go/cmd/clone_list.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package cmd
 
 import (
diff --git a/client/go/cmd/clone_list_test.go b/client/go/cmd/clone_list_test.go
index 9ef4be47c9c..1138e5de064 100644
--- a/client/go/cmd/clone_list_test.go
+++ b/client/go/cmd/clone_list_test.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package cmd
 
 import (
diff --git a/client/go/cmd/clone_test.go b/client/go/cmd/clone_test.go
index 6cf11dd4d40..054dc7b21fb 100644
--- a/client/go/cmd/clone_test.go
+++ b/client/go/cmd/clone_test.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // init command tests
 // Author: bratseth
 
diff --git a/client/go/cmd/command_tester.go b/client/go/cmd/command_tester.go
index 6929b59decb..8eaf6be2c22 100644
--- a/client/go/cmd/command_tester.go
+++ b/client/go/cmd/command_tester.go
@@ -27,6 +27,18 @@ type command struct {
 	moreArgs []string
 }
 
+func resetFlag(f *pflag.Flag) {
+	switch v := f.Value.(type) {
+	case pflag.SliceValue:
+		_ = v.Replace([]string{})
+	default:
+		switch v.Type() {
+		case "bool", "string", "int":
+			_ = v.Set(f.DefValue)
+		}
+	}
+}
+
 func execute(cmd command, t *testing.T, client *mockHttpClient) (string, string) {
 	if client != nil {
 		util.ActiveHttpClient = client
@@ -44,17 +56,8 @@ func execute(cmd command, t *testing.T, client *mockHttpClient) (string, string)
 	os.Setenv("VESPA_CLI_CACHE_DIR", cmd.cacheDir)
 
 	// Reset flags to their default value - persistent flags in Cobra persists over tests
-	rootCmd.Flags().VisitAll(func(f *pflag.Flag) {
-		switch v := f.Value.(type) {
-		case pflag.SliceValue:
-			_ = v.Replace([]string{})
-		default:
-			switch v.Type() {
-			case "bool", "string", "int":
-				_ = v.Set(f.DefValue)
-			}
-		}
-	})
+	rootCmd.Flags().VisitAll(resetFlag)
+	documentCmd.Flags().VisitAll(resetFlag)
 
 	// Do not exit in tests
 	exitFunc = func(code int) {}
diff --git a/client/go/cmd/config.go b/client/go/cmd/config.go
index 863f247bd7c..a5d6a05a048 100644
--- a/client/go/cmd/config.go
+++ b/client/go/cmd/config.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // vespa config command
 // author: bratseth
 
diff --git a/client/go/cmd/config_test.go b/client/go/cmd/config_test.go
index 25ba7cc0655..0e74e53c5e5 100644
--- a/client/go/cmd/config_test.go
+++ b/client/go/cmd/config_test.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package cmd
 
 import (
@@ -9,7 +10,7 @@ import (
 
 func TestConfig(t *testing.T) {
 	homeDir := filepath.Join(t.TempDir(), ".vespa")
-	assertConfigCommand(t, "invalid option or value: \"foo\": \"bar\"\n", homeDir, "config", "set", "foo", "bar")
+	assertConfigCommandErr(t, "invalid option or value: \"foo\": \"bar\"\n", homeDir, "config", "set", "foo", "bar")
 	assertConfigCommand(t, "foo = <unset>\n", homeDir, "config", "get", "foo")
 	assertConfigCommand(t, "target = local\n", homeDir, "config", "get", "target")
 	assertConfigCommand(t, "", homeDir, "config", "set", "target", "cloud")
@@ -18,15 +19,15 @@ func TestConfig(t *testing.T) {
 	assertConfigCommand(t, "", homeDir, "config", "set", "target", "https://127.0.0.1")
 	assertConfigCommand(t, "target = https://127.0.0.1\n", homeDir, "config", "get", "target")
 
-	assertConfigCommand(t, "invalid application: \"foo\"\n", homeDir, "config", "set", "application", "foo")
+	assertConfigCommandErr(t, "invalid application: \"foo\"\n", homeDir, "config", "set", "application", "foo")
 	assertConfigCommand(t, "application = <unset>\n", homeDir, "config", "get", "application")
 	assertConfigCommand(t, "", homeDir, "config", "set", "application", "t1.a1.i1")
 	assertConfigCommand(t, "application = t1.a1.i1\n", homeDir, "config", "get", "application")
 
-	assertConfigCommand(t, "application = t1.a1.i1\ncolor = auto\ntarget = https://127.0.0.1\nwait = 0\n", homeDir, "config", "get")
+	assertConfigCommand(t, "application = t1.a1.i1\ncolor = auto\nquiet = false\ntarget = https://127.0.0.1\nwait = 0\n", homeDir, "config", "get")
 
 	assertConfigCommand(t, "", homeDir, "config", "set", "wait", "60")
-	assertConfigCommand(t, "wait option must be an integer >= 0, got \"foo\"\n", homeDir, "config", "set", "wait", "foo")
+	assertConfigCommandErr(t, "wait option must be an integer >= 0, got \"foo\"\n", homeDir, "config", "set", "wait", "foo")
 	assertConfigCommand(t, "wait = 60\n", homeDir, "config", "get", "wait")
 }
 
@@ -34,3 +35,8 @@ func assertConfigCommand(t *testing.T, expected, homeDir string, args ...string)
 	out, _ := execute(command{homeDir: homeDir, args: args}, t, nil)
 	assert.Equal(t, expected, out)
 }
+
+func assertConfigCommandErr(t *testing.T, expected, homeDir string, args ...string) {
+	_, outErr := execute(command{homeDir: homeDir, args: args}, t, nil)
+	assert.Equal(t, expected, outErr)
+}
diff --git a/client/go/cmd/deploy.go b/client/go/cmd/deploy.go
index b3171d184e0..1380eca5bbb 100644
--- a/client/go/cmd/deploy.go
+++ b/client/go/cmd/deploy.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // vespa deploy command
 // Author: bratseth
 
diff --git a/client/go/cmd/deploy_test.go b/client/go/cmd/deploy_test.go
index 9614806b968..5bb45e70fad 100644
--- a/client/go/cmd/deploy_test.go
+++ b/client/go/cmd/deploy_test.go
@@ -61,9 +61,10 @@ func TestDeployApplicationDirectoryWithPomAndTarget(t *testing.T) {
 
 func TestDeployApplicationDirectoryWithPomAndEmptyTarget(t *testing.T) {
 	client := &mockHttpClient{}
+	_, outErr := execute(command{args: []string{"deploy", "testdata/applications/withEmptyTarget"}}, t, client)
 	assert.Equal(t,
 		"Error: pom.xml exists but no target/application.zip. Run mvn package first\n",
-		executeCommand(t, client, []string{"deploy", "testdata/applications/withEmptyTarget"}, []string{}))
+		outErr)
 }
 
 func TestDeployApplicationPackageErrorWithUnexpectedNonJson(t *testing.T) {
@@ -85,7 +86,7 @@ func TestDeployApplicationPackageErrorWithExpectedFormat(t *testing.T) {
 		"Invalid XML, error in services.xml:\nelement \"nosuch\" not allowed here",
 		`{
          "error-code": "INVALID_APPLICATION_PACKAGE",
-         "message": "Invalid XML, error in services.xml: element \"nosuch\" not allowed here\n"
+         "message": "Invalid XML, error in services.xml: element \"nosuch\" not allowed here"
      }`)
 }
 
@@ -94,7 +95,7 @@ func TestPrepareApplicationPackageErrorWithExpectedFormat(t *testing.T) {
 		"Invalid XML, error in services.xml:\nelement \"nosuch\" not allowed here",
 		`{
          "error-code": "INVALID_APPLICATION_PACKAGE",
-         "message": "Invalid XML, error in services.xml: element \"nosuch\" not allowed here\n"
+         "message": "Invalid XML, error in services.xml: element \"nosuch\" not allowed here"
      }`)
 }
 
@@ -158,18 +159,20 @@ func assertDeployRequestMade(target string, client *mockHttpClient, t *testing.T
 	assertPackageUpload(-1, target+"/application/v2/tenant/default/prepareandactivate", client, t)
 }
 
-func assertApplicationPackageError(t *testing.T, command string, status int, expectedMessage string, returnBody string) {
+func assertApplicationPackageError(t *testing.T, cmd string, status int, expectedMessage string, returnBody string) {
 	client := &mockHttpClient{}
 	client.NextResponse(status, returnBody)
+	_, outErr := execute(command{args: []string{cmd, "testdata/applications/withTarget/target/application.zip"}}, t, client)
 	assert.Equal(t,
 		"Error: Invalid application package (Status "+strconv.Itoa(status)+")\n\n"+expectedMessage+"\n",
-		executeCommand(t, client, []string{command, "testdata/applications/withTarget/target/application.zip"}, []string{}))
+		outErr)
 }
 
 func assertDeployServerError(t *testing.T, status int, errorMessage string) {
 	client := &mockHttpClient{}
 	client.NextResponse(status, errorMessage)
+	_, outErr := execute(command{args: []string{"deploy", "testdata/applications/withTarget/target/application.zip"}}, t, client)
 	assert.Equal(t,
 		"Error: Error from deploy service at 127.0.0.1:19071 (Status "+strconv.Itoa(status)+"):\n"+errorMessage+"\n",
-		executeCommand(t, client, []string{"deploy", "testdata/applications/withTarget/target/application.zip"}, []string{}))
+		outErr)
 }
diff --git a/client/go/cmd/document.go b/client/go/cmd/document.go
index cc5fb948e3b..1d27a475172 100644
--- a/client/go/cmd/document.go
+++ b/client/go/cmd/document.go
@@ -5,9 +5,9 @@
 package cmd
 
 import (
+	"fmt"
 	"io"
 	"io/ioutil"
-	"log"
 	"strings"
 
 	"github.com/spf13/cobra"
@@ -123,20 +123,29 @@ func curlOutput() io.Writer {
 }
 
 func printResult(result util.OperationResult, payloadOnlyOnSuccess bool) {
+	out := stdout
 	if !result.Success {
-		log.Print(color.Red("Error: "), result.Message)
+		out = stderr
+	}
+
+	if !result.Success {
+		fmt.Fprintln(out, color.Red("Error:"), result.Message)
 	} else if !(payloadOnlyOnSuccess && result.Payload != "") {
-		log.Print(color.Green("Success: "), result.Message)
+		fmt.Fprintln(out, color.Green("Success:"), result.Message)
 	}
 
 	if result.Detail != "" {
-		log.Print(color.Yellow(result.Detail))
+		fmt.Fprintln(out, color.Yellow(result.Detail))
 	}
 
 	if result.Payload != "" {
 		if !payloadOnlyOnSuccess {
-			log.Println("")
+			fmt.Fprintln(out)
 		}
-		log.Print(result.Payload)
+		fmt.Fprintln(out, result.Payload)
+	}
+
+	if !result.Success {
+		exitFunc(1)
 	}
 }
diff --git a/client/go/cmd/document_test.go b/client/go/cmd/document_test.go
index 1f82b85f915..649aca8703a 100644
--- a/client/go/cmd/document_test.go
+++ b/client/go/cmd/document_test.go
@@ -67,17 +67,19 @@ func TestDocumentRemoveWithoutIdArg(t *testing.T) {
 func TestDocumentSendMissingId(t *testing.T) {
 	arguments := []string{"document", "put", "testdata/A-Head-Full-of-Dreams-Without-Operation.json"}
 	client := &mockHttpClient{}
+	_, outErr := execute(command{args: arguments}, t, client)
 	assert.Equal(t,
 		"Error: No document id given neither as argument or as a 'put' key in the json file\n",
-		executeCommand(t, client, arguments, []string{}))
+		outErr)
 }
 
 func TestDocumentSendWithDisagreeingOperations(t *testing.T) {
 	arguments := []string{"document", "update", "testdata/A-Head-Full-of-Dreams-Put.json"}
 	client := &mockHttpClient{}
+	_, outErr := execute(command{args: arguments}, t, client)
 	assert.Equal(t,
 		"Error: Wanted document operation is update but the JSON file specifies put\n",
-		executeCommand(t, client, arguments, []string{}))
+		outErr)
 }
 
 func TestDocumentPutDocumentError(t *testing.T) {
@@ -139,21 +141,23 @@ func assertDocumentGet(arguments []string, documentId string, t *testing.T) {
 func assertDocumentError(t *testing.T, status int, errorMessage string) {
 	client := &mockHttpClient{}
 	client.NextResponse(status, errorMessage)
+	_, outErr := execute(command{args: []string{"document", "put",
+		"id:mynamespace:music::a-head-full-of-dreams",
+		"testdata/A-Head-Full-of-Dreams-Put.json"}}, t, client)
 	assert.Equal(t,
 		"Error: Invalid document operation: Status "+strconv.Itoa(status)+"\n\n"+errorMessage+"\n",
-		executeCommand(t, client, []string{"document", "put",
-			"id:mynamespace:music::a-head-full-of-dreams",
-			"testdata/A-Head-Full-of-Dreams-Put.json"}, []string{}))
+		outErr)
 }
 
 func assertDocumentServerError(t *testing.T, status int, errorMessage string) {
 	client := &mockHttpClient{}
 	client.NextResponse(status, errorMessage)
+	_, outErr := execute(command{args: []string{"document", "put",
+		"id:mynamespace:music::a-head-full-of-dreams",
+		"testdata/A-Head-Full-of-Dreams-Put.json"}}, t, client)
 	assert.Equal(t,
 		"Error: Container (document API) at 127.0.0.1:8080: Status "+strconv.Itoa(status)+"\n\n"+errorMessage+"\n",
-		executeCommand(t, client, []string{"document", "put",
-			"id:mynamespace:music::a-head-full-of-dreams",
-			"testdata/A-Head-Full-of-Dreams-Put.json"}, []string{}))
+		outErr)
 }
 
 func documentServiceURL(client *mockHttpClient) string {
diff --git a/client/go/cmd/helpers.go b/client/go/cmd/helpers.go
index 98d6814d16f..b5525cf11fe 100644
--- a/client/go/cmd/helpers.go
+++ b/client/go/cmd/helpers.go
@@ -32,16 +32,16 @@ func fatalErr(err error, msg ...interface{}) {
 func printErrHint(err error, hints ...string) {
 	printErr(nil, err.Error())
 	for _, hint := range hints {
-		log.Print(color.Cyan("Hint: "), hint)
+		fmt.Fprintln(stderr, color.Cyan("Hint:"), hint)
 	}
 }
 
 func printErr(err error, msg ...interface{}) {
 	if len(msg) > 0 {
-		log.Print(color.Red("Error: "), fmt.Sprint(msg...))
+		fmt.Fprintln(stderr, color.Red("Error:"), fmt.Sprint(msg...))
 	}
 	if err != nil {
-		log.Print(color.Yellow(err))
+		fmt.Fprintln(stderr, color.Yellow(err))
 	}
 }
 
@@ -215,11 +215,9 @@ func waitForService(service string, sessionOrRunID int64) {
 	if status/100 == 2 {
 		log.Print(s.Description(), " at ", color.Cyan(s.BaseURL), " is ", color.Green("ready"))
 	} else {
-		log.Print(s.Description(), " at ", color.Cyan(s.BaseURL), " is ", color.Red("not ready"))
 		if err == nil {
-			log.Print(color.Yellow(fmt.Sprintf("Status %d", status)))
-		} else {
-			log.Print(color.Yellow(err))
+			err = fmt.Errorf("Status %d", status)
 		}
+		fatalErr(err, s.Description(), " at ", color.Cyan(s.BaseURL), " is ", color.Red("not ready"))
 	}
 }
diff --git a/client/go/cmd/log.go b/client/go/cmd/log.go
new file mode 100644
index 00000000000..4577e890959
--- /dev/null
+++ b/client/go/cmd/log.go
@@ -0,0 +1,98 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package cmd
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/spf13/cobra"
+	"github.com/vespa-engine/vespa/client/go/vespa"
+)
+
+var (
+	fromArg    string
+	toArg      string
+	levelArg   string
+	followArg  bool
+	dequoteArg bool
+)
+
+func init() {
+	rootCmd.AddCommand(logCmd)
+	logCmd.Flags().StringVarP(&fromArg, "from", "F", "", "Include logs since this timestamp (RFC3339 format)")
+	logCmd.Flags().StringVarP(&toArg, "to", "T", "", "Include logs until this timestamp (RFC3339 format)")
+	logCmd.Flags().StringVarP(&levelArg, "level", "l", "debug", `The maximum log level to show. Must be "error", "warning", "info" or "debug"`)
+	logCmd.Flags().BoolVarP(&followArg, "follow", "f", false, "Follow logs")
+	logCmd.Flags().BoolVarP(&dequoteArg, "nldequote", "n", true, "Dequote LF and TAB characters in log messages")
+}
+
+var logCmd = &cobra.Command{
+	Use:   "log [relative-period]",
+	Short: "Show the Vespa log",
+	Long: `Show the Vespa log.
+
+The logs shown can be limited to a relative or fixed period. All timestamps are shown in UTC.
+`,
+	Example: `$ vespa log 1h
+$ vespa log --nldequote=false 10m
+$ vespa log --from 2021-08-25T15:00:00Z --to 2021-08-26T02:00:00Z
+$ vespa log --follow`,
+	DisableAutoGenTag: true,
+	Args:              cobra.MaximumNArgs(1),
+	Run: func(cmd *cobra.Command, args []string) {
+		target := getTarget()
+		options := vespa.LogOptions{
+			Level:   vespa.LogLevel(levelArg),
+			Follow:  followArg,
+			Writer:  stdout,
+			Dequote: dequoteArg,
+		}
+		if options.Follow {
+			if fromArg != "" || toArg != "" || len(args) > 0 {
+				fatalErr(fmt.Errorf("cannot combine --from/--to or relative time with --follow"), "Could not follow logs")
+			}
+			options.From = time.Now().Add(-5 * time.Minute)
+		} else {
+			from, to, err := parsePeriod(args)
+			if err != nil {
+				fatalErr(err, "Invalid period")
+				return
+			}
+			options.From = from
+			options.To = to
+		}
+		if err := target.PrintLog(options); err != nil {
+			fatalErr(err, "Could not retrieve logs")
+		}
+	},
+}
+
+func parsePeriod(args []string) (time.Time, time.Time, error) {
+	if len(args) == 1 {
+		if fromArg != "" || toArg != "" {
+			return time.Time{}, time.Time{}, fmt.Errorf("cannot combine --from/--to with relative value: %s", args[0])
+		}
+		d, err := time.ParseDuration(args[0])
+		if err != nil {
+			return time.Time{}, time.Time{}, err
+		}
+		if d > 0 {
+			d = -d
+		}
+		to := time.Now()
+		from := to.Add(d)
+		return from, to, nil
+	}
+	from, err := time.Parse(time.RFC3339, fromArg)
+	if err != nil {
+		return time.Time{}, time.Time{}, err
+	}
+	to, err := time.Parse(time.RFC3339, toArg)
+	if err != nil {
+		return time.Time{}, time.Time{}, err
+	}
+	if !to.After(from) {
+		return time.Time{}, time.Time{}, fmt.Errorf("--to must specify a time after --from")
+	}
+	return from, to, nil
+}
diff --git a/client/go/cmd/log_test.go b/client/go/cmd/log_test.go
new file mode 100644
index 00000000000..f239bebc488
--- /dev/null
+++ b/client/go/cmd/log_test.go
@@ -0,0 +1,28 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package cmd
+
+import (
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLog(t *testing.T) {
+	homeDir := filepath.Join(t.TempDir(), ".vespa")
+	pkgDir := mockApplicationPackage(t, false)
+	httpClient := &mockHttpClient{}
+	httpClient.NextResponse(200, `1632738690.905535	host1a.dev.aws-us-east-1c	806/53	logserver-container	Container.com.yahoo.container.jdisc.ConfiguredApplication	info	Switching to the latest deployed set of configurations and components. Application config generation: 52532`)
+	execute(command{homeDir: homeDir, args: []string{"config", "set", "application", "t1.a1.i1"}}, t, httpClient)
+	execute(command{homeDir: homeDir, args: []string{"config", "set", "target", "cloud"}}, t, httpClient)
+	execute(command{homeDir: homeDir, args: []string{"api-key"}}, t, httpClient)
+	execute(command{homeDir: homeDir, args: []string{"cert", pkgDir}}, t, httpClient)
+
+	out, _ := execute(command{homeDir: homeDir, args: []string{"log", "--from", "2021-09-27T10:00:00Z", "--to", "2021-09-27T11:00:00Z"}}, t, httpClient)
+
+	expected := "[2021-09-27 10:31:30.905535] host1a.dev.aws-us-east-1c info    logserver-container Container.com.yahoo.container.jdisc.ConfiguredApplication	Switching to the latest deployed set of configurations and components. Application config generation: 52532\n"
+	assert.Equal(t, expected, out)
+
+	_, errOut := execute(command{homeDir: homeDir, args: []string{"log", "--from", "2021-09-27T13:12:49Z", "--to", "2021-09-27T13:15:00", "1h"}}, t, httpClient)
+	assert.Equal(t, "Error: Invalid period\ncannot combine --from/--to with relative value: 1h\n", errOut)
+}
diff --git a/client/go/cmd/man.go b/client/go/cmd/man.go
index ff7f6fb1b6a..d90898117de 100644
--- a/client/go/cmd/man.go
+++ b/client/go/cmd/man.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package cmd
 
 import (
diff --git a/client/go/cmd/man_test.go b/client/go/cmd/man_test.go
index f7c33c8b3a1..dfbe04f4c8e 100644
--- a/client/go/cmd/man_test.go
+++ b/client/go/cmd/man_test.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package cmd
 
 import (
diff --git a/client/go/cmd/query.go b/client/go/cmd/query.go
index f05914eb9a7..5e2b268865d 100644
--- a/client/go/cmd/query.go
+++ b/client/go/cmd/query.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // vespa query command
 // author: bratseth
 
@@ -47,7 +47,7 @@ func query(arguments []string) {
 
 	response, err := service.Do(&http.Request{URL: url}, time.Second*10)
 	if err != nil {
-		log.Print(color.Red("Error: "), "Request failed: ", err)
+		printErr(nil, "Request failed: ", err)
 		return
 	}
 	defer response.Body.Close()
@@ -55,11 +55,9 @@ func query(arguments []string) {
 	if response.StatusCode == 200 {
 		log.Print(util.ReaderToJSON(response.Body))
 	} else if response.StatusCode/100 == 4 {
-		log.Print(color.Red("Error: "), "Invalid query: ", response.Status, "\n")
-		log.Print(util.ReaderToJSON(response.Body))
+		printErr(nil, "Invalid query: ", response.Status, "\n", util.ReaderToJSON(response.Body))
 	} else {
-		log.Print(color.Red("Error: "), response.Status, " from container at ", color.Cyan(url.Host), "\n")
-		log.Print(util.ReaderToJSON(response.Body))
+		printErr(nil, response.Status, " from container at ", color.Cyan(url.Host), "\n", util.ReaderToJSON(response.Body))
 	}
 }
 
diff --git a/client/go/cmd/query_test.go b/client/go/cmd/query_test.go
index 137ffa01cd5..81dc03766be 100644
--- a/client/go/cmd/query_test.go
+++ b/client/go/cmd/query_test.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // query command tests
 // Author: bratseth
 
@@ -57,18 +57,20 @@ func assertQuery(t *testing.T, expectedQuery string, query ...string) {
 func assertQueryError(t *testing.T, status int, errorMessage string) {
 	client := &mockHttpClient{}
 	client.NextResponse(status, errorMessage)
+	_, outErr := execute(command{args: []string{"query", "yql=select from sources * where title contains 'foo'"}}, t, client)
 	assert.Equal(t,
 		"Error: Invalid query: Status "+strconv.Itoa(status)+"\n"+errorMessage+"\n",
-		executeCommand(t, client, []string{"query"}, []string{"yql=select from sources * where title contains 'foo'"}),
+		outErr,
 		"error output")
 }
 
 func assertQueryServiceError(t *testing.T, status int, errorMessage string) {
 	client := &mockHttpClient{}
 	client.NextResponse(status, errorMessage)
+	_, outErr := execute(command{args: []string{"query", "yql=select from sources * where title contains 'foo'"}}, t, client)
 	assert.Equal(t,
 		"Error: Status "+strconv.Itoa(status)+" from container at 127.0.0.1:8080\n"+errorMessage+"\n",
-		executeCommand(t, client, []string{"query"}, []string{"yql=select from sources * where title contains 'foo'"}),
+		outErr,
 		"error output")
 }
 
diff --git a/client/go/cmd/root.go b/client/go/cmd/root.go
index cd8427c3ac6..7fe704e4918 100644
--- a/client/go/cmd/root.go
+++ b/client/go/cmd/root.go
@@ -6,6 +6,7 @@ package cmd
 
 import (
 	"fmt"
+	"io/ioutil"
 	"log"
 	"os"
 
@@ -36,6 +37,7 @@ Vespa documentation: https://docs.vespa.ai`,
 	applicationArg string
 	waitSecsArg    int
 	colorArg       string
+	quietArg       bool
 
 	color  = aurora.NewAurora(false)
 	stdout = colorable.NewColorableStdout()
@@ -47,17 +49,23 @@ const (
 	targetFlag      = "target"
 	waitFlag        = "wait"
 	colorFlag       = "color"
+	quietFlag       = "quiet"
 )
 
 func isTerminal() bool {
-	file, ok := stdout.(*os.File)
-	if ok {
-		return isatty.IsTerminal(file.Fd())
+	if f, ok := stdout.(*os.File); ok {
+		return isatty.IsTerminal(f.Fd())
+	}
+	if f, ok := stderr.(*os.File); ok {
+		return isatty.IsTerminal(f.Fd())
 	}
 	return false
 }
 
 func configureOutput() {
+	if quietArg {
+		stdout = ioutil.Discard
+	}
 	log.SetFlags(0) // No timestamps
 	log.SetOutput(stdout)
 
@@ -88,10 +96,12 @@ func init() {
 	rootCmd.PersistentFlags().StringVarP(&applicationArg, applicationFlag, "a", "", "The application to manage")
 	rootCmd.PersistentFlags().IntVarP(&waitSecsArg, waitFlag, "w", 0, "Number of seconds to wait for a service to become ready")
 	rootCmd.PersistentFlags().StringVarP(&colorArg, colorFlag, "c", "auto", "Whether to use colors in output. Can be \"auto\", \"never\" or \"always\"")
+	rootCmd.PersistentFlags().BoolVarP(&quietArg, quietFlag, "q", false, "Quiet mode. Only errors are printed.")
 	bindFlagToConfig(targetFlag, rootCmd)
 	bindFlagToConfig(applicationFlag, rootCmd)
 	bindFlagToConfig(waitFlag, rootCmd)
 	bindFlagToConfig(colorFlag, rootCmd)
+	bindFlagToConfig(quietFlag, rootCmd)
 }
 
 // Execute executes the root command.
diff --git a/client/go/cmd/status.go b/client/go/cmd/status.go
index 5fdcaa07d8a..c72df481547 100644
--- a/client/go/cmd/status.go
+++ b/client/go/cmd/status.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // vespa status command
 // author: bratseth
 
diff --git a/client/go/cmd/status_test.go b/client/go/cmd/status_test.go
index 0c1c8e4e3a7..757ef5f3b06 100644
--- a/client/go/cmd/status_test.go
+++ b/client/go/cmd/status_test.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // status command tests
 // Author: bratseth
 
@@ -78,8 +78,11 @@ func assertDocumentStatus(target string, args []string, t *testing.T) {
 func assertQueryStatusError(target string, args []string, t *testing.T) {
 	client := &mockHttpClient{}
 	client.NextStatus(500)
+	cmd := []string{"status", "container"}
+	cmd = append(cmd, args...)
+	_, outErr := execute(command{args: cmd}, t, client)
 	assert.Equal(t,
-		"Container (query API) at "+target+" is not ready\nStatus 500\n",
-		executeCommand(t, client, []string{"status", "container"}, args),
+		"Error: Container (query API) at "+target+" is not ready\nStatus 500\n",
+		outErr,
 		"vespa status container")
 }
diff --git a/client/go/cmd/version.go b/client/go/cmd/version.go
index 749d17a41d9..d2760402851 100644
--- a/client/go/cmd/version.go
+++ b/client/go/cmd/version.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package cmd
 
 import (
diff --git a/client/go/cmd/version_test.go b/client/go/cmd/version_test.go
index 9eeaaaa4692..039f75a6ecd 100644
--- a/client/go/cmd/version_test.go
+++ b/client/go/cmd/version_test.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package cmd
 
 import (
diff --git a/client/go/cmd/vespa/main.go b/client/go/cmd/vespa/main.go
index 73183da2a16..5fdf64f5ab4 100644
--- a/client/go/cmd/vespa/main.go
+++ b/client/go/cmd/vespa/main.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // Cobra commands main file
 // Author: bratseth
 
diff --git a/client/go/util/http.go b/client/go/util/http.go
index a8e2dbc2195..acd9bb4f7ec 100644
--- a/client/go/util/http.go
+++ b/client/go/util/http.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // A HTTP wrapper which handles some errors and provides a way to replace the HTTP client by a mock.
 // Author: bratseth
 
diff --git a/client/go/util/http_test.go b/client/go/util/http_test.go
index 47c710bb068..0a0de1fdd4c 100644
--- a/client/go/util/http_test.go
+++ b/client/go/util/http_test.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // Basic testing of our HTTP client wrapper
 // Author: bratseth
 
diff --git a/client/go/util/io.go b/client/go/util/io.go
index 51361e344f0..f51c6060cb7 100644
--- a/client/go/util/io.go
+++ b/client/go/util/io.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // File utilities.
 // Author: bratseth
 
diff --git a/client/go/util/operation_result.go b/client/go/util/operation_result.go
index fba73a68dc9..5e79f727d4e 100644
--- a/client/go/util/operation_result.go
+++ b/client/go/util/operation_result.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // A struct containing the result of an operation
 // Author: bratseth
 
diff --git a/client/go/version/version.go b/client/go/version/version.go
index 27b7da1d0f5..00e26d25135 100644
--- a/client/go/version/version.go
+++ b/client/go/version/version.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package version
 
 import (
diff --git a/client/go/version/version_test.go b/client/go/version/version_test.go
index 3602715cca8..759b1c1d0c1 100644
--- a/client/go/version/version_test.go
+++ b/client/go/version/version_test.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package version
 
 import (
diff --git a/client/go/vespa/crypto.go b/client/go/vespa/crypto.go
index fb336b88210..b4a5a5b7da8 100644
--- a/client/go/vespa/crypto.go
+++ b/client/go/vespa/crypto.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package vespa
 
 import (
diff --git a/client/go/vespa/crypto_test.go b/client/go/vespa/crypto_test.go
index 87d6587c850..89d50d15d70 100644
--- a/client/go/vespa/crypto_test.go
+++ b/client/go/vespa/crypto_test.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package vespa
 
 import (
diff --git a/client/go/vespa/deploy.go b/client/go/vespa/deploy.go
index 19319724d18..eec0182b0ce 100644
--- a/client/go/vespa/deploy.go
+++ b/client/go/vespa/deploy.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // vespa deploy API
 // Author: bratseth
 
diff --git a/client/go/vespa/deploy_test.go b/client/go/vespa/deploy_test.go
index 32b31eebf7c..d353dafca19 100644
--- a/client/go/vespa/deploy_test.go
+++ b/client/go/vespa/deploy_test.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package vespa
 
 import (
diff --git a/client/go/vespa/id.go b/client/go/vespa/id.go
index ad6e289586e..b0dc770ad52 100644
--- a/client/go/vespa/id.go
+++ b/client/go/vespa/id.go
@@ -1,4 +1,4 @@
-// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 // vespa document ids
 // Author: bratseth
 
diff --git a/client/go/vespa/id_test.go b/client/go/vespa/id_test.go
index 61183465186..343affc1602 100644
--- a/client/go/vespa/id_test.go
+++ b/client/go/vespa/id_test.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package vespa
 
 import (
diff --git a/client/go/vespa/log.go b/client/go/vespa/log.go
new file mode 100644
index 00000000000..0e2cb5d0bfd
--- /dev/null
+++ b/client/go/vespa/log.go
@@ -0,0 +1,100 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package vespa
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+	"time"
+)
+
+var dequoter = strings.NewReplacer("\\n", "\n", "\\t", "\t")
+
+// LogEntry represents a Vespa log entry.
+type LogEntry struct {
+	Time      time.Time
+	Host      string
+	Service   string
+	Component string
+	Level     string
+	Message   string
+}
+
+func (le *LogEntry) Format(dequote bool) string {
+	t := le.Time.Format("2006-01-02 15:04:05.000000")
+	msg := le.Message
+	if dequote {
+		msg = dequoter.Replace(msg)
+	}
+	return fmt.Sprintf("[%s] %-8s %-7s %-16s %s\t%s", t, le.Host, le.Level, le.Service, le.Component, msg)
+}
+
+// ParseLogEntry parses a Vespa log entry from string s.
+func ParseLogEntry(s string) (LogEntry, error) {
+	parts := strings.SplitN(s, "\t", 7)
+	if len(parts) != 7 {
+		return LogEntry{}, fmt.Errorf("invalid number of log parts: %d: %q", len(parts), s)
+	}
+	time, err := parseLogTimestamp(parts[0])
+	if err != nil {
+		return LogEntry{}, err
+	}
+	return LogEntry{
+		Time:      time,
+		Host:      parts[1],
+		Service:   parts[3],
+		Component: parts[4],
+		Level:     parts[5],
+		Message:   parts[6],
+	}, nil
+}
+
+// ReadLogEntries reads and parses all log entries from reader r.
+func ReadLogEntries(r io.Reader) ([]LogEntry, error) {
+	var entries []LogEntry
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		line := scanner.Text()
+		logEntry, err := ParseLogEntry(line)
+		if err != nil {
+			return nil, err
+		}
+		entries = append(entries, logEntry)
+	}
+	if err := scanner.Err(); err != nil {
+		return nil, err
+	}
+	return entries, nil
+}
+
+// LogLevel returns an int representing a named log level.
+func LogLevel(name string) int {
+	switch name {
+	case "error":
+		return 0
+	case "warning":
+		return 1
+	case "info":
+		return 2
+	default: // everything else, e.g. debug
+		return 3
+	}
+}
+
+func parseLogTimestamp(s string) (time.Time, error) {
+	parts := strings.Split(s, ".")
+	if len(parts) != 2 {
+		return time.Time{}, fmt.Errorf("invalid number of log timestamp parts: %d", len(parts))
+	}
+	unixSecs, err := strconv.ParseInt(parts[0], 10, 64)
+	if err != nil {
+		return time.Time{}, fmt.Errorf("invalid timestamp seconds: %s", parts[0])
+	}
+	unixMicros, err := strconv.ParseInt(parts[1], 10, 64)
+	if err != nil {
+		return time.Time{}, fmt.Errorf("invalid timestamp microseconds: %s", parts[1])
+	}
+	return time.Unix(unixSecs, unixMicros*1000).UTC(), nil
+}
diff --git a/client/go/vespa/log_test.go b/client/go/vespa/log_test.go
new file mode 100644
index 00000000000..2d0c75d0a0a
--- /dev/null
+++ b/client/go/vespa/log_test.go
@@ -0,0 +1,32 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package vespa
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestParseLogEntry(t *testing.T) {
+	expected := LogEntry{
+		Time:      time.Date(2021, 9, 27, 10, 31, 30, 905535000, time.UTC),
+		Host:      "host1a.dev.aws-us-east-1c",
+		Service:   "logserver-container",
+		Component: "Container.com.yahoo.container.jdisc.ConfiguredApplication",
+		Level:     "info",
+		Message:   "Switching to the latest deployed set of configurations and components. Application config generation: 52532",
+	}
+	in := "1632738690.905535	host1a.dev.aws-us-east-1c	806/53	logserver-container	Container.com.yahoo.container.jdisc.ConfiguredApplication	info	Switching to the latest deployed set of configurations and components. Application config generation: 52532"
+	logEntry, err := ParseLogEntry(in)
+	assert.Nil(t, err)
+	assert.Equal(t, expected, logEntry)
+
+	formatted := "[2021-09-27 10:31:30.905535] host1a.dev.aws-us-east-1c info    logserver-container Container.com.yahoo.container.jdisc.ConfiguredApplication\tSwitching to the latest deployed set of configurations and components. Application config generation: 52532"
+	assert.Equal(t, formatted, logEntry.Format(false))
+
+	in = "1632738690.905535	host1a.dev.aws-us-east-1c	806/53	logserver-container	Container.com.yahoo.container.jdisc.ConfiguredApplication	info	message containing newline\\nand\\ttab"
+	logEntry, err = ParseLogEntry(in)
+	assert.Nil(t, err)
+	assert.Equal(t, "[2021-09-27 10:31:30.905535] host1a.dev.aws-us-east-1c info    logserver-container Container.com.yahoo.container.jdisc.ConfiguredApplication\tmessage containing newline\nand\ttab", logEntry.Format(true))
+}
diff --git a/client/go/vespa/target.go b/client/go/vespa/target.go
index aa0ddb8babb..8a09440f5cc 100644
--- a/client/go/vespa/target.go
+++ b/client/go/vespa/target.go
@@ -1,11 +1,14 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package vespa
 
 import (
+	"bytes"
 	"crypto/tls"
 	"encoding/json"
 	"fmt"
 	"io"
 	"io/ioutil"
+	"math"
 	"net/http"
 	"net/url"
 	"sort"
@@ -41,6 +44,9 @@ type Target interface {
 
 	// Service returns the service for given name. If timeout is non-zero, wait for the service to converge.
 	Service(name string, timeout time.Duration, sessionOrRunID int64) (*Service, error)
+
+	// PrintLog writes the logs of this deployment using given options to control output.
+	PrintLog(options LogOptions) error
 }
 
 // TLSOptions configures the certificate to use for service requests.
@@ -50,10 +56,14 @@ type TLSOptions struct {
 	PrivateKeyFile  string
 }
 
-// LogOptions configures the log output to produce when waiting for services.
+// LogOptions configures the log output to produce when writing log messages.
 type LogOptions struct {
-	Writer io.Writer
-	Level  int
+	From    time.Time
+	To      time.Time
+	Follow  bool
+	Dequote bool
+	Writer  io.Writer
+	Level   int
 }
 
 type customTarget struct {
@@ -119,6 +129,10 @@ func (t *customTarget) Service(name string, timeout time.Duration, sessionID int
 	return nil, fmt.Errorf("unknown service: %s", name)
 }
 
+func (t *customTarget) PrintLog(options LogOptions) error {
+	return fmt.Errorf("reading logs from non-cloud deployment is currently unsupported")
+}
+
 func (t *customTarget) urlWithPort(serviceName string) (string, error) {
 	u, err := url.Parse(t.baseURL)
 	if err != nil {
@@ -207,6 +221,64 @@ func (t *cloudTarget) Service(name string, timeout time.Duration, runID int64) (
 	return nil, fmt.Errorf("unknown service: %s", name)
 }
 
+func (t *cloudTarget) logsURL() string {
+	return fmt.Sprintf("%s/application/v4/tenant/%s/application/%s/instance/%s/environment/%s/region/%s/logs",
+		t.apiURL,
+		t.deployment.Application.Tenant, t.deployment.Application.Application, t.deployment.Application.Instance,
+		t.deployment.Zone.Environment, t.deployment.Zone.Region)
+}
+
+func (t *cloudTarget) PrintLog(options LogOptions) error {
+	req, err := http.NewRequest("GET", t.logsURL(), nil)
+	if err != nil {
+		return err
+	}
+	signer := NewRequestSigner(t.deployment.Application.SerializedForm(), t.apiKey)
+	lastFrom := options.From
+	requestFunc := func() *http.Request {
+		fromMillis := lastFrom.Unix() * 1000
+		q := req.URL.Query()
+		q.Set("from", strconv.FormatInt(fromMillis, 10))
+		if !options.To.IsZero() {
+			toMillis := options.To.Unix() * 1000
+			q.Set("to", strconv.FormatInt(toMillis, 10))
+		}
+		req.URL.RawQuery = q.Encode()
+		if err := signer.SignRequest(req); err != nil {
+			panic(err)
+		}
+		return req
+	}
+	logFunc := func(status int, response []byte) (bool, error) {
+		if ok, err := isOK(status); !ok {
+			return ok, err
+		}
+		logEntries, err := ReadLogEntries(bytes.NewReader(response))
+		if err != nil {
+			return true, err
+		}
+		for _, le := range logEntries {
+			if !le.Time.After(lastFrom) {
+				continue
+			}
+			if LogLevel(le.Level) > options.Level {
+				continue
+			}
+			fmt.Fprintln(options.Writer, le.Format(options.Dequote))
+		}
+		if len(logEntries) > 0 {
+			lastFrom = logEntries[len(logEntries)-1].Time
+		}
+		return false, nil
+	}
+	var timeout time.Duration
+	if options.Follow {
+		timeout = math.MaxInt64 // No timeout
+	}
+	_, err = wait(logFunc, requestFunc, &t.tlsOptions.KeyPair, timeout)
+	return err
+}
+
 func (t *cloudTarget) waitForEndpoints(timeout time.Duration, runID int64) error {
 	signer := NewRequestSigner(t.deployment.Application.SerializedForm(), t.apiKey)
 	if runID > 0 {
@@ -348,20 +420,6 @@ func CloudTarget(apiURL string, deployment Deployment, apiKey []byte, tlsOptions
 	}
 }
 
-// LogLevel returns an int representing a named log level.
-func LogLevel(name string) int {
-	switch name {
-	case "error":
-		return 0
-	case "warning":
-		return 1
-	case "info":
-		return 2
-	default: // everything else, e.g. debug
-		return 3
-	}
-}
-
 type deploymentEndpoint struct {
 	URL string `json:"url"`
 }
diff --git a/client/go/vespa/target_test.go b/client/go/vespa/target_test.go
index 2c90baefbbc..ed924059297 100644
--- a/client/go/vespa/target_test.go
+++ b/client/go/vespa/target_test.go
@@ -1,9 +1,12 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package vespa
 
 import (
 	"bytes"
 	"crypto/tls"
 	"fmt"
+	"io"
+	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -40,6 +43,11 @@ func (v *mockVespaApi) mockVespaHandler(w http.ResponseWriter, req *http.Request
 	case "/application/v2/tenant/default/application/default/environment/prod/region/default/instance/default/serviceconverge":
 		response := fmt.Sprintf(`{"converged": %t}`, v.deploymentConverged)
 		w.Write([]byte(response))
+	case "/application/v4/tenant/t1/application/a1/instance/i1/environment/dev/region/us-north-1/logs":
+		log := `1632738690.905535	host1a.dev.aws-us-east-1c	806/53	logserver-container	Container.com.yahoo.container.jdisc.ConfiguredApplication	info	Switching to the latest deployed set of configurations and components. Application config generation: 52532
+1632738698.600189	host1a.dev.aws-us-east-1c	1723/33590	config-sentinel	sentinel.sentinel.config-owner	config	Sentinel got 3 service elements [tenant(vespa-team), application(music), instance(mpolden)] for config generation 52532
+`
+		w.Write([]byte(log))
 	case "/status.html":
 		w.Write([]byte("OK"))
 	case "/ApplicationStatus":
@@ -92,6 +100,44 @@ func TestCloudTargetWait(t *testing.T) {
 	defer srv.Close()
 	vc.serverURL = srv.URL
 
+	var logWriter bytes.Buffer
+	target := createCloudTarget(t, srv.URL, &logWriter)
+	assertServiceWait(t, 200, target, "deploy")
+
+	_, err := target.Service("query", time.Millisecond, 42)
+	assert.NotNil(t, err)
+
+	vc.deploymentConverged = true
+	_, err = target.Service("query", time.Millisecond, 42)
+	assert.Nil(t, err)
+
+	assertServiceWait(t, 500, target, "query")
+	assertServiceWait(t, 500, target, "document")
+
+	// Log timestamp is converted to local time, do the same here in case the local time where tests are run varies
+	tm := time.Unix(1631707708, 431000)
+	expectedTime := tm.Format("[15:04:05]")
+	assert.Equal(t, expectedTime+" info    Deploying platform version 7.465.17 and application version 1.0.2 ...\n", logWriter.String())
+}
+
+func TestLog(t *testing.T) {
+	vc := mockVespaApi{}
+	srv := httptest.NewServer(http.HandlerFunc(vc.mockVespaHandler))
+	defer srv.Close()
+	vc.serverURL = srv.URL
+	vc.deploymentConverged = true
+
+	var buf bytes.Buffer
+	target := createCloudTarget(t, srv.URL, ioutil.Discard)
+	if err := target.PrintLog(LogOptions{Writer: &buf, Level: 3}); err != nil {
+		t.Fatal(err)
+	}
+	expected := "[2021-09-27 10:31:30.905535] host1a.dev.aws-us-east-1c info    logserver-container Container.com.yahoo.container.jdisc.ConfiguredApplication\tSwitching to the latest deployed set of configurations and components. Application config generation: 52532\n" +
+		"[2021-09-27 10:31:38.600189] host1a.dev.aws-us-east-1c config  config-sentinel  sentinel.sentinel.config-owner\tSentinel got 3 service elements [tenant(vespa-team), application(music), instance(mpolden)] for config generation 52532\n"
+	assert.Equal(t, expected, buf.String())
+}
+
+func createCloudTarget(t *testing.T, url string, logWriter io.Writer) Target {
 	kp, err := CreateKeyPair()
 	assert.Nil(t, err)
 
@@ -100,7 +146,6 @@ func TestCloudTargetWait(t *testing.T) {
 	apiKey, err := CreateAPIKey()
 	assert.Nil(t, err)
 
-	var logWriter bytes.Buffer
 	target := CloudTarget(
 		"https://example.com",
 		Deployment{
@@ -109,28 +154,13 @@ func TestCloudTargetWait(t *testing.T) {
 		},
 		apiKey,
 		TLSOptions{KeyPair: x509KeyPair},
-		LogOptions{Writer: &logWriter})
+		LogOptions{Writer: logWriter})
 	if ct, ok := target.(*cloudTarget); ok {
-		ct.apiURL = srv.URL
+		ct.apiURL = url
 	} else {
 		t.Fatalf("Wrong target type %T", ct)
 	}
-	assertServiceWait(t, 200, target, "deploy")
-
-	_, err = target.Service("query", time.Millisecond, 42)
-	assert.NotNil(t, err)
-
-	vc.deploymentConverged = true
-	_, err = target.Service("query", time.Millisecond, 42)
-	assert.Nil(t, err)
-
-	assertServiceWait(t, 500, target, "query")
-	assertServiceWait(t, 500, target, "document")
-
-	// Log timestamp is converted to local time, do the same here in case the local time where tests are run varies
-	tm := time.Unix(1631707708, 431000)
-	expectedTime := tm.Format("[15:04:05]")
-	assert.Equal(t, expectedTime+" info    Deploying platform version 7.465.17 and application version 1.0.2 ...\n", logWriter.String())
+	return target
 }
 
 func assertServiceURL(t *testing.T, url string, target Target, service string) {
diff --git a/client/go/vespa/version.go b/client/go/vespa/version.go
index e5a89f4cb58..b20c6d360d7 100644
--- a/client/go/vespa/version.go
+++ b/client/go/vespa/version.go
@@ -1,3 +1,4 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package vespa
 
 // Version is the Vespa CLI version number