Support file templates

17 files changed, 667 insertions, 57 deletions

diff --git a/node-admin/pom.xml b/node-admin/pom.xml
index 983e4d3a832..161769a4edf 100644
--- a/node-admin/pom.xml
+++ b/node-admin/pom.xml
@@ -115,8 +115,12 @@
             <artifactId>mockito-core</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.apache.velocity</groupId>
+            <artifactId>velocity</artifactId>
+            <scope>compile</scope>
+        </dependency>
     </dependencies>
-
     <build>
         <plugins>
             <plugin>
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileAttributes.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileAttributes.java
new file mode 100644
index 00000000000..c99d5850909
--- /dev/null
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileAttributes.java
@@ -0,0 +1,22 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+package com.yahoo.vespa.hosted.node.admin.task.util.file;
+
+import java.nio.file.attribute.PosixFileAttributes;
+import java.nio.file.attribute.PosixFilePermissions;
+import java.time.Instant;
+
+public class FileAttributes {
+    private final PosixFileAttributes attributes;
+
+    FileAttributes(PosixFileAttributes attributes) {
+        this.attributes = attributes;
+    }
+
+    public Instant lastModifiedTime() { return attributes.lastModifiedTime().toInstant(); }
+    public String owner() { return attributes.owner().getName(); }
+    public String group() { return attributes.group().getName(); }
+    public String permissions() { return PosixFilePermissions.toString(attributes.permissions()); }
+    public boolean isRegularFile() { return attributes.isRegularFile(); }
+    public boolean isDirectory() { return attributes.isDirectory(); }
+}
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileAttributesCache.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileAttributesCache.java
new file mode 100644
index 00000000000..12a9609f89c
--- /dev/null
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileAttributesCache.java
@@ -0,0 +1,44 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+package com.yahoo.vespa.hosted.node.admin.task.util.file;
+
+import java.util.Optional;
+
+// @ThreadUnsafe
+public class FileAttributesCache {
+    private final UnixPath path;
+
+    private Optional<FileAttributes> attributes = Optional.empty();
+
+    public FileAttributesCache(UnixPath path) {
+        this.path =  path;
+    }
+
+    public FileAttributes get() {
+        if (!attributes.isPresent()) {
+            attributes = Optional.of(path.getAttributes());
+        }
+
+        return attributes.get();
+    }
+
+    public FileAttributes forceGet() {
+        attributes = Optional.empty();
+        return get();
+    }
+
+    public boolean exists() {
+        if (attributes.isPresent()) {
+            return true;
+        }
+
+        Optional<FileAttributes> attributes = path.getAttributesIfExists();
+        if (attributes.isPresent()) {
+            // Might as well update this.attributes
+            this.attributes = attributes;
+            return true;
+        } else {
+            return false;
+        }
+    }
+}
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileContentCache.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileContentCache.java
new file mode 100644
index 00000000000..ac50ff0cbab
--- /dev/null
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileContentCache.java
@@ -0,0 +1,34 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+package com.yahoo.vespa.hosted.node.admin.task.util.file;
+
+import java.time.Instant;
+import java.util.Optional;
+
+/**
+ * Class to avoid repeated reads of file content when the file seldom changes.
+ */
+class FileContentCache {
+    private final UnixPath path;
+
+    private Optional<String> value = Optional.empty();
+    private Optional<Instant> modifiedTime = Optional.empty();
+
+    FileContentCache(UnixPath path) {
+        this.path = path;
+    }
+
+    String get(Instant lastModifiedTime) {
+        if (!value.isPresent() || lastModifiedTime.compareTo(modifiedTime.get()) > 0) {
+            value = Optional.of(path.readUtf8File());
+            modifiedTime = Optional.of(lastModifiedTime);
+        }
+
+        return value.get();
+    }
+
+    void updateWith(String content, Instant modifiedTime) {
+        this.value = Optional.of(content);
+        this.modifiedTime = Optional.of(modifiedTime);
+    }
+}
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileSync.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileSync.java
new file mode 100644
index 00000000000..f103ab394ef
--- /dev/null
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileSync.java
@@ -0,0 +1,116 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+package com.yahoo.vespa.hosted.node.admin.task.util.file;
+
+import com.yahoo.vespa.hosted.node.admin.component.TaskContext;
+
+import java.nio.file.Path;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+import java.util.logging.Logger;
+
+/**
+ * Class to minimize resource usage with repetitive and mostly identical, idempotent, and
+ * mutating file operations, e.g. setting file content, setting owner, etc.
+ *
+ * Only changes to the file is logged.
+ */
+// @ThreadUnsafe
+public class FileSync {
+    private static final Logger logger = Logger.getLogger(FileSync.class.getName());
+
+    private final UnixPath path;
+    private final FileContentCache contentCache;
+
+    public FileSync(Path path) {
+        this.path = new UnixPath(path);
+        this.contentCache = new FileContentCache(this.path);
+    }
+
+    /**
+     * CPU, I/O, and memory usage is optimized for repeated calls with the same arguments.
+     * @return true if the system was modified: content was written, or owner was set, etc.
+     *         system is only modified if necessary (different).
+     */
+    public boolean convergeTo(TaskContext taskContext, PartialFileData partialFileData) {
+        FileAttributesCache currentAttributes = new FileAttributesCache(path);
+
+        boolean modifiedSystem = false;
+
+        modifiedSystem |= maybeUpdateContent(taskContext, partialFileData.getContent(), currentAttributes);
+
+        modifiedSystem |= convergeAttribute(
+                taskContext,
+                "owner",
+                partialFileData.getOwner(),
+                () -> currentAttributes.get().owner(),
+                path::setOwner);
+
+        modifiedSystem |= convergeAttribute(
+                taskContext,
+                "group",
+                partialFileData.getGroup(),
+                () -> currentAttributes.get().group(),
+                path::setGroup);
+
+        modifiedSystem |= convergeAttribute(
+                taskContext,
+                "permissions",
+                partialFileData.getPermissions(),
+                () -> currentAttributes.get().permissions(),
+                path::setPermissions);
+
+        return modifiedSystem;
+    }
+
+    private boolean convergeAttribute(TaskContext taskContext,
+                                      String attributeName,
+                                      Optional<String> wantedValue,
+                                      Supplier<String> currentValueSupplier,
+                                      Consumer<String> valueSetter) {
+        if (!wantedValue.isPresent()) {
+            return false;
+        }
+
+        String currentValue = currentValueSupplier.get();
+        if (Objects.equals(wantedValue.get(), currentValue)) {
+            return false;
+        } else {
+            String actionDescription = String.format("Changing %s of %s from %s to %s",
+                    attributeName,
+                    path,
+                    currentValue,
+                    wantedValue.get());
+            taskContext.logSystemModification(logger, actionDescription);
+            valueSetter.accept(wantedValue.get());
+            return true;
+        }
+    }
+
+    private boolean maybeUpdateContent(TaskContext taskContext,
+                                       Optional<String> content,
+                                       FileAttributesCache currentAttributes) {
+        if (!content.isPresent()) {
+            return false;
+        }
+
+        if (!currentAttributes.exists()) {
+            taskContext.logSystemModification(logger, "Creating file " + path);
+            path.createParents();
+            path.writeUtf8File(content.get());
+            contentCache.updateWith(content.get(), currentAttributes.forceGet().lastModifiedTime());
+            return true;
+        }
+
+        if (Objects.equals(content.get(), contentCache.get(currentAttributes.get().lastModifiedTime()))) {
+            return false;
+        } else {
+            taskContext.logSystemModification(logger, "Patching file " + path);
+            path.writeUtf8File(content.get());
+            contentCache.updateWith(content.get(), currentAttributes.forceGet().lastModifiedTime());
+            return true;
+        }
+    }
+}
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileWriter.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileWriter.java
index 60a7b3482b2..2f22c94781f 100644
--- a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileWriter.java
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileWriter.java
@@ -6,56 +6,48 @@ import org.glassfish.jersey.internal.util.Producer;
 
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.util.Optional;
-import java.util.logging.Logger;
 
 public class FileWriter {
-    private static final Logger logger = Logger.getLogger(FileWriter.class.getName());
-
     private final Path path;
+    private final FileSync fileSync;
+    private final PartialFileData.Builder fileDataBuilder = PartialFileData.builder();
     private final Producer<String> contentProducer;
 
-    private Optional<String> owner = Optional.empty();
-    private Optional<String> group = Optional.empty();
-    private Optional<String> permissions = Optional.empty();
+    private boolean overwriteExistingFile = true;
 
     public FileWriter(Path path, Producer<String> contentProducer) {
         this.path = path;
+        this.fileSync = new FileSync(path);
         this.contentProducer = contentProducer;
     }
 
     public FileWriter withOwner(String owner) {
-        this.owner = Optional.of(owner);
+        fileDataBuilder.withOwner(owner);
         return this;
     }
 
     public FileWriter withGroup(String group) {
-        this.group = Optional.of(group);
+        fileDataBuilder.withGroup(group);
         return this;
     }
 
     public FileWriter withPermissions(String permissions) {
-        this.permissions = Optional.of(permissions);
+        fileDataBuilder.withPermissions(permissions);
+        return this;
+    }
+
+    public FileWriter onlyIfFileDoesNotAlreadyExist() {
+        overwriteExistingFile = false;
         return this;
     }
 
     public boolean converge(TaskContext context) {
-        // TODO: Only return false if content, permission, etc would be unchanged.
-        if (Files.isRegularFile(path)) {
+        if (!overwriteExistingFile && Files.isRegularFile(path)) {
             return false;
         }
 
-        context.logSystemModification(logger,"Writing file " + path);
-
-        String content = contentProducer.call();
-
-        UnixPath unixPath = new UnixPath(path);
-        unixPath.createParents();
-        unixPath.writeUtf8File(content);
-        permissions.ifPresent(unixPath::setPermissions);
-        owner.ifPresent(unixPath::setOwner);
-        group.ifPresent(unixPath::setGroup);
-
-        return true;
+        fileDataBuilder.withContent(contentProducer.call());
+        PartialFileData fileData = fileDataBuilder.create();
+        return fileSync.convergeTo(context, fileData);
     }
 }
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/IOExceptionUtil.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/IOExceptionUtil.java
index dee5525d42a..ef553a131e8 100644
--- a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/IOExceptionUtil.java
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/IOExceptionUtil.java
@@ -1,8 +1,10 @@
 // Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.vespa.hosted.node.admin.task.util.file;
 
+import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.UncheckedIOException;
+import java.util.Optional;
 
 public class IOExceptionUtil {
     public static <T> void uncheck(RunnableThrowingIOException<T> runnable) {
@@ -31,4 +33,20 @@ public class IOExceptionUtil {
     public interface RunnableThrowingIOException<T> {
         void run() throws IOException;
     }
+
+    /**
+     * Useful if it's not known whether a file or directory exists, in case e.g.
+     * FileNotFoundException is thrown and the caller wants an Optional.empty() in that case.
+     */
+    public static <T> Optional<T> ifExists(SupplierThrowingIOException<T> supplier) {
+        try {
+            return Optional.ofNullable(uncheck(supplier));
+        } catch (UncheckedIOException e) {
+            if (e.getCause() instanceof FileNotFoundException) {
+                return Optional.empty();
+            }
+
+            throw e;
+        }
+    }
 }
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/PartialFileData.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/PartialFileData.java
new file mode 100644
index 00000000000..d29c01179f2
--- /dev/null
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/PartialFileData.java
@@ -0,0 +1,62 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+package com.yahoo.vespa.hosted.node.admin.task.util.file;
+
+import java.util.Optional;
+
+/**
+ * Represents a subset of a file's content, owner, group, and permissions.
+ */
+// @Immutable
+public class PartialFileData {
+    private final Optional<String> content;
+    private final Optional<String> owner;
+    private final Optional<String> group;
+    private final Optional<String> permissions;
+
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    public PartialFileData(Optional<String> content,
+                           Optional<String> owner,
+                           Optional<String> group,
+                           Optional<String> permissions) {
+        this.content = content;
+        this.owner = owner;
+        this.group = group;
+        this.permissions = permissions;
+    }
+
+    public Optional<String> getContent() {
+        return content;
+    }
+
+    public Optional<String> getOwner() {
+        return owner;
+    }
+
+    public Optional<String> getGroup() {
+        return group;
+    }
+
+    public Optional<String> getPermissions() {
+        return permissions;
+    }
+
+    public static class Builder {
+        private Optional<String> content = Optional.empty();
+        private Optional<String> owner = Optional.empty();
+        private Optional<String> group = Optional.empty();
+        private Optional<String> permissions = Optional.empty();
+
+        public Builder withContent(String content) { this.content = Optional.of(content); return this; }
+        public Builder withOwner(String owner) { this.owner = Optional.of(owner); return this; }
+        public Builder withGroup(String group) { this.group = Optional.of(group); return this; }
+        public Builder withPermissions(String permissions) { this.permissions = Optional.of(permissions); return this; }
+
+        public PartialFileData create() {
+            return new PartialFileData(content, owner, group, permissions);
+        }
+    }
+}
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/TemplateFile.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/TemplateFile.java
new file mode 100644
index 00000000000..1d5b5f42cf3
--- /dev/null
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/TemplateFile.java
@@ -0,0 +1,42 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.hosted.node.admin.task.util.file;
+
+import org.apache.velocity.Template;
+import org.apache.velocity.VelocityContext;
+import org.apache.velocity.app.Velocity;
+import org.apache.velocity.app.VelocityEngine;
+
+import java.io.StringWriter;
+import java.nio.file.Path;
+
+public class TemplateFile {
+    private final Path templatePath;
+    private final VelocityEngine velocityEngine;
+    private final VelocityContext velocityContext = new VelocityContext();
+
+    public TemplateFile(Path templatePath) {
+        this.templatePath = templatePath;
+        velocityEngine = new VelocityEngine();
+        velocityEngine.addProperty(
+                Velocity.RUNTIME_LOG_LOGSYSTEM_CLASS,
+                "org.apache.velocity.runtime.log.NullLogSystem");
+        velocityEngine.addProperty(Velocity.FILE_RESOURCE_LOADER_PATH, templatePath.getParent().toString());
+        velocityEngine.init();
+    }
+
+    public TemplateFile set(String name, String value) {
+        velocityContext.put(name, value);
+        return this;
+    }
+
+    public FileWriter getFileWriterTo(Path destinationPath) {
+        return new FileWriter(destinationPath, this::render);
+    }
+
+    private String render() {
+        Template template = velocityEngine.getTemplate(templatePath.getFileName().toString(), "UTF-8");
+        StringWriter writer = new StringWriter();
+        template.merge(velocityContext, writer);
+        return writer.toString();
+    }
+}
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/UnixPath.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/UnixPath.java
index 606f8cfb06e..a83d79a97a9 100644
--- a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/UnixPath.java
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/UnixPath.java
@@ -1,10 +1,10 @@
 // Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.vespa.hosted.node.admin.task.util.file;
 
-import java.io.IOException;
 import java.io.UncheckedIOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
+import java.nio.file.NoSuchFileException;
 import java.nio.file.OpenOption;
 import java.nio.file.Path;
 import java.nio.file.Paths;
@@ -16,8 +16,11 @@ import java.nio.file.attribute.PosixFilePermissions;
 import java.nio.file.attribute.UserPrincipal;
 import java.nio.file.attribute.UserPrincipalLookupService;
 import java.time.Instant;
+import java.util.Optional;
 import java.util.Set;
 
+import static com.yahoo.vespa.hosted.node.admin.task.util.file.IOExceptionUtil.uncheck;
+
 // @Immutable
 public class UnixPath {
     private final Path path;
@@ -34,8 +37,14 @@ public class UnixPath {
         return path;
     }
 
-    public void createParents() {
-        uncheck(() -> Files.createDirectories(path.getParent()));
+    public boolean createParents() {
+        Path parent = path.getParent();
+        if (Files.isDirectory(parent)) {
+            return false;
+        }
+
+        uncheck(() -> Files.createDirectories(parent));
+        return true;
     }
 
     public String readUtf8File() {
@@ -49,7 +58,7 @@ public class UnixPath {
     }
 
     public String getPermissions() {
-        return PosixFilePermissions.toString(getAttributes().permissions());
+        return getAttributes().permissions();
     }
 
     /**
@@ -69,7 +78,7 @@ public class UnixPath {
     }
 
     public String getOwner() {
-        return getAttributes().owner().getName();
+        return getAttributes().owner();
     }
 
     public void setOwner(String owner) {
@@ -79,7 +88,7 @@ public class UnixPath {
     }
 
     public String getGroup() {
-        return getAttributes().group().getName();
+        return getAttributes().group();
     }
 
     public void setGroup(String group) {
@@ -89,37 +98,29 @@ public class UnixPath {
     }
 
     public Instant getLastModifiedTime() {
-        return uncheck(() -> Files.getLastModifiedTime(path)).toInstant();
+        return getAttributes().lastModifiedTime();
     }
 
-    private PosixFileAttributes getAttributes() {
-        return uncheck(() ->
+    public FileAttributes getAttributes() {
+        PosixFileAttributes attributes = uncheck(() ->
                 Files.getFileAttributeView(path, PosixFileAttributeView.class).readAttributes());
+        return new FileAttributes(attributes);
     }
 
-    @FunctionalInterface
-    private interface SupplierThrowingIOException<T> {
-        T get() throws IOException;
-    }
-
-    private static <T> T uncheck(SupplierThrowingIOException<T> supplier) {
+    public Optional<FileAttributes> getAttributesIfExists() {
         try {
-            return supplier.get();
-        } catch (IOException e) {
-            throw new UncheckedIOException(e);
-        }
-    }
+            return Optional.of(getAttributes());
+        } catch (UncheckedIOException e) {
+            if (e.getCause() instanceof NoSuchFileException) {
+                return Optional.empty();
+            }
 
-    @FunctionalInterface
-    private interface RunnableThrowingIOException<T> {
-        void run() throws IOException;
+            throw e;
+        }
     }
 
-    private static <T> void uncheck(RunnableThrowingIOException<T> runnable) {
-        try {
-            runnable.run();
-        } catch (IOException e) {
-            throw new UncheckedIOException(e);
-        }
+    @Override
+    public String toString() {
+        return path.toString();
     }
 }
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/yum/AddYumRepo.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/yum/AddYumRepo.java
index 9ca1c0286f9..d6dbc3cd12a 100644
--- a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/yum/AddYumRepo.java
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/yum/AddYumRepo.java
@@ -32,7 +32,8 @@ public class AddYumRepo {
         FileWriter fileWriter = new FileWriter(path, this::getRepoFileContent)
                 .withOwner("root")
                 .withGroup("root")
-                .withPermissions("rw-r--r--");
+                .withPermissions("rw-r--r--")
+                .onlyIfFileDoesNotAlreadyExist();
 
         return fileWriter.converge(context);
     }
diff --git a/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileAttributesCacheTest.java b/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileAttributesCacheTest.java
new file mode 100644
index 00000000000..9224faf1c6f
--- /dev/null
+++ b/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileAttributesCacheTest.java
@@ -0,0 +1,38 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+package com.yahoo.vespa.hosted.node.admin.task.util.file;
+
+import org.junit.Test;
+
+import java.util.Optional;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoMoreInteractions;
+import static org.mockito.Mockito.when;
+
+public class FileAttributesCacheTest {
+    @Test
+    public void exists() throws Exception {
+        UnixPath unixPath = mock(UnixPath.class);
+        FileAttributesCache cache = new FileAttributesCache(unixPath);
+
+        when(unixPath.getAttributesIfExists()).thenReturn(Optional.empty());
+        assertFalse(cache.exists());
+        verify(unixPath, times(1)).getAttributesIfExists();
+        verifyNoMoreInteractions(unixPath);
+
+        FileAttributes attributes = mock(FileAttributes.class);
+        when(unixPath.getAttributesIfExists()).thenReturn(Optional.of(attributes));
+        assertTrue(cache.exists());
+        verify(unixPath, times(1 + 1)).getAttributesIfExists();
+        verifyNoMoreInteractions(unixPath);
+
+        assertEquals(attributes, cache.get());
+        verifyNoMoreInteractions(unixPath);
+    }
+}
\ No newline at end of file
diff --git a/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileContentCacheTest.java b/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileContentCacheTest.java
new file mode 100644
index 00000000000..677dd048445
--- /dev/null
+++ b/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileContentCacheTest.java
@@ -0,0 +1,58 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+package com.yahoo.vespa.hosted.node.admin.task.util.file;
+
+import org.junit.Test;
+
+import java.time.Instant;
+
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoMoreInteractions;
+import static org.mockito.Mockito.when;
+
+public class FileContentCacheTest {
+    private final UnixPath unixPath = mock(UnixPath.class);
+    private final FileContentCache cache = new FileContentCache(unixPath);
+
+    @Test
+    public void get() throws Exception {
+        when(unixPath.readUtf8File()).thenReturn("content");
+        assertEquals("content", cache.get(Instant.ofEpochMilli(0)));
+        verify(unixPath, times(1)).readUtf8File();
+        verifyNoMoreInteractions(unixPath);
+
+        // cache hit
+        assertEquals("content", cache.get(Instant.ofEpochMilli(0)));
+        verify(unixPath, times(1)).readUtf8File();
+        verifyNoMoreInteractions(unixPath);
+
+        // cache miss
+        when(unixPath.readUtf8File()).thenReturn("new-content");
+        assertEquals("new-content", cache.get(Instant.ofEpochMilli(1)));
+        verify(unixPath, times(1 + 1)).readUtf8File();
+        verifyNoMoreInteractions(unixPath);
+
+        // cache hit both at times 0 and 1
+        assertEquals("new-content", cache.get(Instant.ofEpochMilli(0)));
+        verify(unixPath, times(1 + 1)).readUtf8File();
+        verifyNoMoreInteractions(unixPath);
+        assertEquals("new-content", cache.get(Instant.ofEpochMilli(1)));
+        verify(unixPath, times(1 + 1)).readUtf8File();
+        verifyNoMoreInteractions(unixPath);
+    }
+
+    @Test
+    public void updateWith() throws Exception {
+        cache.updateWith("content", Instant.ofEpochMilli(2));
+        assertEquals("content", cache.get(Instant.ofEpochMilli(2)));
+        verifyNoMoreInteractions(unixPath);
+
+        cache.updateWith("new-content", Instant.ofEpochMilli(4));
+        assertEquals("new-content", cache.get(Instant.ofEpochMilli(4)));
+        verifyNoMoreInteractions(unixPath);
+    }
+
+}
\ No newline at end of file
diff --git a/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileSyncTest.java b/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileSyncTest.java
new file mode 100644
index 00000000000..71cd312d5d6
--- /dev/null
+++ b/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileSyncTest.java
@@ -0,0 +1,83 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+package com.yahoo.vespa.hosted.node.admin.task.util.file;
+
+import org.junit.Test;
+
+import java.nio.file.FileSystem;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class FileSyncTest {
+    private final TestTaskContext taskContext = new TestTaskContext();
+    private final FileSystem fileSystem = taskContext.fileSystem();
+
+    private final Path path = fileSystem.getPath("/dir/file.txt");
+    private final UnixPath unixPath = new UnixPath(path);
+    private final FileSync fileSync = new FileSync(path);
+
+    private String content = "content";
+    private String owner = "owner"; // default is user
+    private String group = "group1"; // default is group
+    private String permissions = "rw-r-xr--";
+
+    @Test
+    public void trivial() {
+        assertConvergence("Creating file /dir/file.txt",
+                "Changing owner of /dir/file.txt from user to owner",
+                "Changing group of /dir/file.txt from group to group1",
+                "Changing permissions of /dir/file.txt from rw-r--r-- to rw-r-xr--");
+
+        content = "new-content";
+        assertConvergence("Patching file /dir/file.txt");
+
+        owner = "new-owner";
+        assertConvergence("Changing owner of /dir/file.txt from owner to " +
+                        owner);
+
+        group = "new-group1";
+        assertConvergence("Changing group of /dir/file.txt from group1 to new-group1");
+
+        permissions = "rwxr--rwx";
+        assertConvergence("Changing permissions of /dir/file.txt from rw-r-xr-- to " +
+                permissions);
+    }
+
+    private void assertConvergence(String... systemModificationMessages) {
+        PartialFileData fileData = PartialFileData.builder()
+                .withContent(content)
+                .withOwner(owner)
+                .withGroup(group)
+                .withPermissions(permissions)
+                .create();
+        taskContext.clearSystemModificationLog();
+        assertTrue(fileSync.convergeTo(taskContext, fileData));
+
+        assertTrue(Files.isRegularFile(path));
+        fileData.getContent().ifPresent(content -> assertEquals(content, unixPath.readUtf8File()));
+        fileData.getOwner().ifPresent(owner -> assertEquals(owner, unixPath.getOwner()));
+        fileData.getGroup().ifPresent(group -> assertEquals(group, unixPath.getGroup()));
+        fileData.getPermissions().ifPresent(permissions -> assertEquals(permissions, unixPath.getPermissions()));
+
+        List<String> actualMods = taskContext.getSystemModificationLog();
+        List<String> expectedMods = Arrays.asList(systemModificationMessages);
+        assertEquals(expectedMods, actualMods);
+
+        UnixPath unixPath = new UnixPath(path);
+        Instant lastModifiedTime = unixPath.getLastModifiedTime();
+        taskContext.clearSystemModificationLog();
+        assertFalse(fileSync.convergeTo(taskContext, fileData));
+        assertEquals(lastModifiedTime, unixPath.getLastModifiedTime());
+
+        actualMods = taskContext.getSystemModificationLog();
+        assertEquals(new ArrayList<>(), actualMods);
+    }
+}
\ No newline at end of file
diff --git a/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileWriterTest.java b/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileWriterTest.java
index 878b1e4cbdb..bb8ca2586c8 100644
--- a/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileWriterTest.java
+++ b/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileWriterTest.java
@@ -33,10 +33,11 @@ public class FileWriterTest {
         FileWriter writer = new FileWriter(path, () -> content)
                 .withPermissions(permissions)
                 .withOwner(owner)
-                .withGroup(group);
+                .withGroup(group)
+                .onlyIfFileDoesNotAlreadyExist();
         TaskContext context = mock(TaskContext.class);
         assertTrue(writer.converge(context));
-        verify(context, times(1)).logSystemModification(any(), eq("Writing file " + path));
+        verify(context, times(1)).logSystemModification(any(), eq("Creating file " + path));
 
         UnixPath unixPath = new UnixPath(path);
         assertEquals(content, unixPath.readUtf8File());
diff --git a/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/TemplateFileTest.java b/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/TemplateFileTest.java
new file mode 100644
index 00000000000..b1d88fdaaee
--- /dev/null
+++ b/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/TemplateFileTest.java
@@ -0,0 +1,49 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+package com.yahoo.vespa.hosted.node.admin.task.util.file;
+
+import com.yahoo.vespa.hosted.node.admin.component.TaskContext;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.IOException;
+import java.nio.file.Path;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+
+/**
+ * WARNING: Velocity does not honor an alternative FileSystem like JimFS.
+ */
+public class TemplateFileTest {
+    @Rule
+    public TemporaryFolder folder = new TemporaryFolder();
+
+    private void writeFile(Path path, String content) {
+        UnixPath unixPath = new UnixPath(path);
+        unixPath.createParents();
+        unixPath.writeUtf8File(content);
+    }
+
+    @Test
+    public void basic() throws IOException {
+        String templateContent = "a $x, $y b";
+        Path templatePath = folder.newFile("example.vm").toPath();
+        writeFile(templatePath, templateContent);
+
+        Path toPath = folder.newFile().toPath();
+        TaskContext taskContext = mock(TaskContext.class);
+        boolean converged = new TemplateFile(templatePath)
+                .set("x", "foo")
+                .set("y", "bar")
+                .getFileWriterTo(toPath)
+                .converge(taskContext);
+
+        assertTrue(converged);
+
+        String actualContent = new UnixPath(toPath).readUtf8File();
+        assertEquals("a foo, bar b", actualContent);
+    }
+}
\ No newline at end of file
diff --git a/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/TestTaskContext.java b/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/TestTaskContext.java
new file mode 100644
index 00000000000..d023a11671e
--- /dev/null
+++ b/node-admin/src/test/java/com/yahoo/vespa/hosted/node/admin/task/util/file/TestTaskContext.java
@@ -0,0 +1,45 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+package com.yahoo.vespa.hosted.node.admin.task.util.file;
+
+import com.yahoo.vespa.hosted.node.admin.component.TaskContext;
+import com.yahoo.vespa.test.file.TestFileSystem;
+
+import java.nio.file.FileSystem;
+import java.util.ArrayList;
+import java.util.EnumSet;
+import java.util.List;
+import java.util.logging.Logger;
+
+public class TestTaskContext implements TaskContext {
+    private final FileSystem fileSystem = TestFileSystem.create();
+    private final List<String> logs = new ArrayList<>();
+
+    @Override
+    public Cloud cloud() {
+        return Cloud.YAHOO;
+    }
+
+    @Override
+    public EnumSet<Role> roles() {
+        return EnumSet.of(Role.CONFIG_SERVER_DOCKER_HOST);
+    }
+
+    @Override
+    public FileSystem fileSystem() {
+        return fileSystem;
+    }
+
+    @Override
+    public void logSystemModification(Logger logger, String actionDescription) {
+        logs.add(actionDescription);
+    }
+
+    public List<String> getSystemModificationLog() {
+        return logs;
+    }
+
+    public void clearSystemModificationLog() {
+        logs.clear();
+    }
+}