feat: Support CRaC priming for powertools-tracing and powertools-serialization #2104

dcabib · 2025-09-01T14:18:31Z

Summary

Adds support for CRaC priming in both the powertools-tracing and powertools-serialization modules to improve AWS Lambda SnapStart restore durations.

Changes

Add org.crac dependency and generate-classesloaded-file profile to both modules
Implement Resource interface in TracingUtils and JsonConfig classes
Add classesloaded.txt files for automatic class preloading
Add comprehensive CRaC tests for both modules
Update documentation with SnapStart priming guidance
Update spotbugs-exclude.xml for beforeCheckpoint methods

Implementation Details

Tracing Module:

TracingUtils implements Resource interface with CRaC hooks
X-Ray SDK priming with dummy calls (no trace persistence)
Direct TracingUtils reference requirement documented

Serialization Module:

JsonConfig implements Resource interface with CRaC hooks
Comprehensive AWS Lambda event types priming
Jackson ObjectMapper and JMESPath warming

Both implementations follow the exact same patterns established in PR #2081 for the validation module.

Testing

All existing tests continue to pass (no regressions)
New CRaC-specific tests added for both modules
Clean build and comprehensive testing completed

Issue numbers: #2004 and #2003

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

…alization - Add CRaC dependency and generate-classesloaded-file profile to both modules - Implement Resource interface in TracingUtils and JsonConfig classes - Add classesloaded.txt files for automatic class preloading - Add comprehensive CRaC tests for both modules - Update documentation with SnapStart priming guidance - Update spotbugs-exclude.xml for beforeCheckpoint methods Addresses issues aws-powertools#2004 and aws-powertools#2003

phipag

Hey @dcabib,

thanks for sending this PR. I added a couple of comments.

After implemented, I will test this in my AWS account to see if the runtime hooks get correctly executed at runtime when publishing a SnapStart enabled Lambda version using these dependencies.

phipag · 2025-09-01T14:49:51Z

...ools-serialization/src/main/java/software/amazon/lambda/powertools/utilities/JsonConfig.java

+        getObjectMapper();
+        getJmesPath();


This is not needed since we load it below anyway.

phipag · 2025-09-01T14:53:14Z

...ools-serialization/src/main/java/software/amazon/lambda/powertools/utilities/JsonConfig.java

+        try {
+            ObjectMapper mapper = getObjectMapper();
+
+            // Prime common AWS Lambda event types as suggested by Philipp
+            primeEventType(mapper, "com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent", 
+                "{\"httpMethod\":\"GET\",\"path\":\"/test\",\"headers\":{\"Content-Type\":\"application/json\"}}");
+            primeEventType(mapper, "com.amazonaws.services.lambda.runtime.events.APIGatewayV2HTTPEvent", 
+                "{\"version\":\"2.0\",\"routeKey\":\"GET /test\",\"requestContext\":{\"http\":{\"method\":\"GET\"}}}");
+            primeEventType(mapper, "com.amazonaws.services.lambda.runtime.events.SQSEvent", 
+                "{\"Records\":[{\"messageId\":\"test\",\"body\":\"test message\"}]}");
+            primeEventType(mapper, "com.amazonaws.services.lambda.runtime.events.SNSEvent", 
+                "{\"Records\":[{\"Sns\":{\"Message\":\"test message\",\"TopicArn\":\"arn:aws:sns:us-east-1:123456789012:test\"}}]}");
+            primeEventType(mapper, "com.amazonaws.services.lambda.runtime.events.KinesisEvent", 
+                "{\"Records\":[{\"kinesis\":{\"data\":\"dGVzdA==\",\"partitionKey\":\"test\"}}]}");
+            primeEventType(mapper, "com.amazonaws.services.lambda.runtime.events.ScheduledEvent", 
+                "{\"source\":\"aws.events\",\"detail-type\":\"Scheduled Event\"}");
+
+            // Warm up JMESPath function registry
+            getJmesPath().compile("@").search(mapper.readTree("{\"test\":\"value\"}"));
+
+        } catch (Exception e) {
+            // Ignore exceptions during priming as they're expected in some environments
+        }


This doesn't have any side-effects and we should aim at not catching an exception at all.

Can you generate realistic events that pass Jackson loading?

Why are you loading the event classes reflectively using Class<?> eventClass = Class.forName(className);? I don't think this is necessary – let's import them directly and parse the generated fake events using mapper.readValue(fakeEvent, SQSEvent.class).

I think you can use sam cli to generate fake events https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-cli-command-reference-sam-local-generate-event.html

phipag · 2025-09-01T14:54:30Z

...ialization/src/test/java/software/amazon/lambda/powertools/utilities/JsonConfigCracTest.java

+    @Test
+    void testBeforeCheckpointDoesNotThrowException() {
+        assertThatNoException().isThrownBy(() -> config.beforeCheckpoint(context));
+    }
+
+    @Test
+    void testAfterRestoreDoesNotThrowException() {
+        assertThatNoException().isThrownBy(() -> config.afterRestore(context));
+    }


After removing the exception wildcard catch these tests should still pass. Right now, they have no effect.

See comment: https://github.com/aws-powertools/powertools-lambda-java/pull/2104/files#r2314166695

phipag · 2025-09-01T14:57:00Z

powertools-tracing/src/main/java/software/amazon/lambda/powertools/tracing/TracingUtils.java

+        } catch (Exception e) {
+            // Ignore exceptions during priming as they're expected in some environments
+            LOG.debug("Exception during X-Ray priming (expected in some environments): {}", e.getMessage());
+        }


Can you check if we can remove this exception catching as well?

phipag · 2025-09-01T14:57:44Z

powertools-tracing/src/main/java/software/amazon/lambda/powertools/tracing/TracingUtils.java

+        // Preload classes
+        ClassPreLoader.preloadClasses();


Let's move pre-load classes to the top of beforeCheckpoint everywhere? This makes sure that this always runs even if something else throws an exception at runtime. It has dedicated unit tests making sure that this is reliable.

phipag · 2025-09-01T14:58:45Z

...ls-tracing/src/test/java/software/amazon/lambda/powertools/tracing/TracingUtilsCracTest.java

+        // Access the private INSTANCE field using reflection
+        Field instanceField = TracingUtils.class.getDeclaredField("INSTANCE");
+        instanceField.setAccessible(true);
+        TracingUtils tracingUtils = (TracingUtils) instanceField.get(null);


Why is this necessary?

phipag · 2025-09-01T15:00:10Z

spotbugs-exclude.xml

+            <And>
+                <Class name="software.amazon.lambda.powertools.utilities.JsonConfig"/>
+                <Method name="beforeCheckpoint"/>
+            </And>


I believe we can remove this again after implementing my comment about JsonConfig priming. If it is still needed let's keep it there.

phipag · 2025-09-01T15:02:43Z

docs/core/tracing.md

+=== "Constructor"
+
+    ```java hl_lines="7"
+    import software.amazon.lambda.powertools.tracing.Tracing;
+    import software.amazon.lambda.powertools.tracing.TracingUtils;
+
+    public class MyFunctionHandler implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
+
+        public MyFunctionHandler() {
+            TracingUtils.putAnnotation("init", "priming"); // Ensure TracingUtils is loaded for SnapStart
+        }
+
+        @Override
+        @Tracing
+        public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent input, Context context) {
+            // ...
+            return something;
+        }
+    }
+    ```
+
+=== "Static Initializer"
+
+    ```java hl_lines="7"
+    import software.amazon.lambda.powertools.tracing.Tracing;
+    import software.amazon.lambda.powertools.tracing.TracingUtils;
+
+    public class MyFunctionHandler implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
+
+        static {
+            TracingUtils.putAnnotation("init", "priming"); // Ensure TracingUtils is loaded for SnapStart
+        }
+
+        @Override
+        @Tracing
+        public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent input, Context context) {
+            // ...
+            return something;
+        }
+    }
+    ```


I think we should expand TracingUtils with a method TracingUtils.prime() that has no side-effects unlike the example given here. As a user, I don't want to be forced to add e.g. an annotation to my traces just to trigger SnapStart priming.

- Add TracingUtils.prime() method with no side-effects for public API - Move ClassPreLoader.preloadClasses() to top of beforeCheckpoint methods - Remove unnecessary exception catching in CRaC hooks - Update JsonConfig to use direct imports instead of reflection for AWS Lambda events - Fix CRaC tests to not use reflection for accessing private fields - Update documentation examples to use TracingUtils.prime() - Consolidate SpotBugs exclusions into single Or structure All CRaC tests passing (4 tests, 0 failures)

sonarqubecloud · 2025-09-01T15:14:28Z

Quality Gate passed

Issues
5 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

phipag · 2025-09-04T14:49:24Z

Hey @dcabib, if possible, let's split this PR in two PRs please since it addresses two separate issues. It will be easier to address comments on a smaller scale since I see some of my comments were ignored in the recent push and all of them were left unanswered.

dcabib · 2025-09-05T11:47:15Z

Closing this PR as requested by @phipag to split into separate PRs.

This has been addressed with:

PR feat: Support CRaC priming for powertools-tracing #2121: CRaC priming for powertools-tracing
PR feat: Support CRaC priming for powertools-serialization #2122: CRaC priming for powertools-serialization

Both separate PRs are now ready for review with all SonarQube issues resolved and all tests passing.

pull-request-size bot added the size/XL label Sep 1, 2025

phipag requested changes Sep 1, 2025

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dcabib closed this Sep 5, 2025

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dcabib commented Sep 1, 2025

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Testing

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