2 files changed, 44 insertions, 7 deletions

diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/component/TaskContext.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/component/TaskContext.java
index 2d94db3d96e..d0a5570b8dc 100644
--- a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/component/TaskContext.java
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/component/TaskContext.java
@@ -1,6 +1,7 @@
 // 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.component;
 
+import java.util.function.Supplier;
 import java.util.logging.Logger;
 
 public interface TaskContext {
@@ -16,10 +17,39 @@ public interface TaskContext {
      *     performed (sometimes this is not possible).
      *
      * @param logger Used to log the modification to help locate the source of the modification.
-     * @param description Description of the modification, e.g. "Changing owner of /foo from alice
-     *                    to bob".
+     * @param message Description of the modification, e.g. "Changing owner of /foo from alice
+     *                to bob".
      */
-    void recordSystemModification(Logger logger, String description);
+    void recordSystemModification(Logger logger, String message);
+    default void recordSystemModification(Logger logger, String messageFormat, String... args) {
+        recordSystemModification(logger, String.format(messageFormat, (Object[]) args));
+    }
+
+    /**
+     * Log message at LogLevel.INFO, scoped to denote the current task. The message may
+     * also be directed to status pages or similar.
+     *
+     * Please do not call this too many times as that spams the log. Typically a task may call
+     * this zero times, or up to a few times.
+     *
+     * Do not log a message that is also recorded with recordSystemModification.
+     */
+    default void log(Logger logger, String message) {}
+    default void log(Logger logger, String messageFormat, String... args) {
+        log(logger, String.format(messageFormat, (Object[]) args));
+    }
+
+    /**
+     * Register a message supplier to be called if the task failed, to help with debugging
+     * of the task (and too verbose to log at every run). The message is also logged at
+     * LogLevel.DEBUG if enabled.
+     *
+     * Do not call logOnFailure for a message passed to either recordSystemModification or log.
+     *
+     * @param messageSupplier Supplier to be called possibly immediately (if DEBUG is enabled),
+     *                        or later if the task failed. Either way, it will only be called once.
+     */
+    default void logOnFailure(Logger logger, Supplier<String> messageSupplier) {}
 
     /**
      * Execute a task as a child of this task, and with its own sub-TaskContext. Please  avoid
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/component/TestTaskContext.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/component/TestTaskContext.java
index 6806e5096c5..108d42114f7 100644
--- a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/component/TestTaskContext.java
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/component/TestTaskContext.java
@@ -4,22 +4,29 @@ package com.yahoo.vespa.hosted.node.admin.component;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.Supplier;
 import java.util.logging.Logger;
 
 public class TestTaskContext implements TaskContext {
-    private final List<String> logs = new ArrayList<>();
+    private final List<String> systemModifications = new ArrayList<>();
 
     @Override
     public void recordSystemModification(Logger logger, String description) {
-        logs.add(description);
+        systemModifications.add(description);
     }
 
+    @Override
+    public void log(Logger logger, String message) { }
+
+    @Override
+    public void logOnFailure(Logger logger, Supplier<String> messageSupplier) { }
+
     public List<String> getSystemModificationLog() {
-        return logs;
+        return systemModifications;
     }
 
     public void clearSystemModificationLog() {
-        logs.clear();
+        systemModifications.clear();
     }
 
     @Override