[8.x] Truncate step_info and error reason in ILM execution state and history (#125054)

docs/changelog/125054.yaml

@@ -0,0 +1,6 @@
+pr: 125054
+summary: Truncate `step_info` and error reason in ILM execution state and history
+area: ILM+SLM
+type: enhancement
+issues:
+ - 124181

server/src/main/java/org/elasticsearch/cluster/metadata/LifecycleExecutionState.java

@@ -10,6 +10,7 @@
 package org.elasticsearch.cluster.metadata;
 
 import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.common.Strings;
 
 import java.util.Collections;
 import java.util.HashMap;
@@ -42,6 +43,7 @@ public record LifecycleExecutionState(
 ) {
 
     public static final String ILM_CUSTOM_METADATA_KEY = "ilm";
+    public static final int MAXIMUM_STEP_INFO_STRING_LENGTH = 1024;
 
     private static final String PHASE = "phase";
     private static final String ACTION = "action";
@@ -267,6 +269,17 @@ public Map<String, String> asMap() {
         return Collections.unmodifiableMap(result);
     }
 
+    public static String truncateWithExplanation(String input) {
+        if (input != null && input.length() > MAXIMUM_STEP_INFO_STRING_LENGTH) {
+            return Strings.cleanTruncate(input, MAXIMUM_STEP_INFO_STRING_LENGTH)
+                + "... ("
+                + (input.length() - MAXIMUM_STEP_INFO_STRING_LENGTH)
+                + " chars truncated)";
+        } else {
+            return input;
+        }
+    }
+
     public static class Builder {
         private String phase;
         private String action;
@@ -308,7 +321,7 @@ public Builder setFailedStep(String failedStep) {
         }
 
         public Builder setStepInfo(String stepInfo) {
-            this.stepInfo = stepInfo;
+            this.stepInfo = truncateWithExplanation(stepInfo);
             return this;
         }
 

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ilm/LifecycleExecutionStateTests.java

@@ -14,6 +14,8 @@
 import java.util.HashMap;
 import java.util.Map;
 
+import static org.hamcrest.Matchers.equalTo;
+
 public class LifecycleExecutionStateTests extends ESTestCase {
 
     public void testConversion() {
@@ -22,6 +24,20 @@ public void testConversion() {
         assertEquals(customMetadata, parsed.asMap());
     }
 
+    public void testTruncatingStepInfo() {
+        Map<String, String> custom = createCustomMetadata();
+        LifecycleExecutionState state = LifecycleExecutionState.fromCustomMetadata(custom);
+        assertThat(custom.get("step_info"), equalTo(state.stepInfo()));
+        String longStepInfo = randomAlphanumericOfLength(LifecycleExecutionState.MAXIMUM_STEP_INFO_STRING_LENGTH + 100);
+        LifecycleExecutionState newState = LifecycleExecutionState.builder(state).setStepInfo(longStepInfo).build();
+        // Length includes the post suffix
+        assertThat(newState.stepInfo().length(), equalTo(LifecycleExecutionState.MAXIMUM_STEP_INFO_STRING_LENGTH + 25));
+        assertThat(
+            newState.stepInfo().substring(LifecycleExecutionState.MAXIMUM_STEP_INFO_STRING_LENGTH, 1049),
+            equalTo("... (100 chars truncated)")
+        );
+    }
+
     public void testEmptyValuesAreNotSerialized() {
         LifecycleExecutionState empty = LifecycleExecutionState.builder().build();
         assertEquals(new HashMap<String, String>().entrySet(), empty.asMap().entrySet());

x-pack/plugin/ilm/src/main/java/org/elasticsearch/xpack/ilm/history/ILMHistoryItem.java

@@ -86,7 +86,15 @@ public static ILMHistoryItem failure(
         Exception error
     ) {
         Objects.requireNonNull(error, "ILM failures require an attached exception");
-        return new ILMHistoryItem(index, policyId, timestamp, indexAge, false, executionState, exceptionToString(error));
+        String fullErrorString = exceptionToString(error);
+        String truncatedErrorString = LifecycleExecutionState.truncateWithExplanation(fullErrorString);
+        if (truncatedErrorString.equals(fullErrorString) == false) {
+            // Append a closing quote and closing brace to attempt to make it valid JSON.
+            // There is no requirement that it actually be valid JSON, so this is
+            // best-effort, but does not cause problems if it is still invalid.
+            truncatedErrorString += "\"}";
+        }
+        return new ILMHistoryItem(index, policyId, timestamp, indexAge, false, executionState, truncatedErrorString);
     }
 
     @Override

x-pack/plugin/ilm/src/test/java/org/elasticsearch/xpack/ilm/history/ILMHistoryItemTests.java

@@ -13,8 +13,13 @@
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.xcontent.ToXContent;
 import org.elasticsearch.xcontent.XContentBuilder;
+import org.elasticsearch.xcontent.XContentFactory;
+import org.elasticsearch.xcontent.XContentParser;
+import org.elasticsearch.xcontent.XContentParserConfiguration;
+import org.elasticsearch.xcontent.XContentType;
 
 import java.io.IOException;
+import java.util.Map;
 
 import static org.elasticsearch.xcontent.XContentFactory.jsonBuilder;
 import static org.hamcrest.Matchers.equalTo;
@@ -111,4 +116,35 @@ public void testToXContent() throws IOException {
                 \\"stack_trace\\":\\"java.lang.IllegalArgumentException: failure""".replaceAll("\\s", "")));
         }
     }
+
+    public void testTruncateLongError() throws IOException {
+        String longError = randomAlphaOfLength(LifecycleExecutionState.MAXIMUM_STEP_INFO_STRING_LENGTH + 20);
+
+        ILMHistoryItem failure = ILMHistoryItem.failure(
+            "index",
+            "policy",
+            1234L,
+            100L,
+            LifecycleExecutionState.EMPTY_STATE,
+            new IllegalArgumentException(longError)
+        );
+
+        try (XContentBuilder builder = jsonBuilder()) {
+            failure.toXContent(builder, ToXContent.EMPTY_PARAMS);
+            String json = Strings.toString(builder);
+            try (XContentParser p = XContentFactory.xContent(XContentType.JSON).createParser(XContentParserConfiguration.EMPTY, json)) {
+                Map<String, Object> item = p.map();
+                assertThat(
+                    item.get("error_details"),
+                    equalTo(
+                        "{\"type\":\"illegal_argument_exception\",\"reason\":\""
+                            // We subtract a number of characters here due to the truncation being based
+                            // on the length of the whole string, not just the "reason" part.
+                            + longError.substring(0, LifecycleExecutionState.MAXIMUM_STEP_INFO_STRING_LENGTH - 47)
+                            + "... (5126 chars truncated)\"}"
+                    )
+                );
+            }
+        }
+    }
 }