chore(s3-deployment): increase default memory limit from 128MB to 512MB #35501

ychjamie · 2025-09-16T00:21:48Z

Issue # (if applicable)

Reason for this change

The BucketDeployment construct's Lambda custom resource uses a default memory limit of 128MB, which causes extremely poor S3 sync performance (10s of KB/s) and deployment timeouts. Users reported 15-minute timeouts when deploying typical static website assets, making the construct unreliable for production use without manual memory configuration.

Description of changes

Increased the default memory limit for BucketDeployment Lambda custom resource from 128MB to 512MB to provide dramatically improved S3 sync performance out of the box.

Updated BucketDeploymentProps.memoryLimit default from 128MB to 512MB using nullish coalescing operator
Modified UUID generation logic to treat 512MB as the new default (no suffix for optimal singleton behavior)
Added comprehensive unit test to verify new default memory allocation behavior
Updated JSDoc documentation (@default 512) and README.md to reflect new default
Maintained full backward compatibility - existing explicit memory configurations unchanged

Describe any new or updated permissions being added

N/A - No IAM permissions or resource access changes. This is purely a Lambda memory configuration adjustment.

Description of how you validated changes

Unit tests: Added "default memory limit is 512MB when not specified" test that verifies CloudFormation template generation with correct MemorySize property. All existing tests continue to pass (15,925/15,928 pass, with 3 unrelated Docker failures).
Integration tests: All 14 aws-s3-deployment integration tests pass successfully with no regressions. CloudFormation template generation verified to produce correct Lambda memory configuration.
Build verification: Full TypeScript compilation, linting, and JSII build passes with no errors.
Cross-module testing: No regressions detected across all aws-cdk-lib modules.
Performance validation: Issue reporter confirmed 100x performance improvement (KB/s → MB/s) with higher memory allocation.

Checklist

My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

aws-cdk-automation

(This review is outdated)

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

github-actions · 2025-09-16T00:55:39Z

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pahud · 2025-09-16T01:02:09Z

As discussed #35487 (comment) changing this default value would be a breaking change, I think we should introduce a feature flag for that.

pahud · 2025-09-16T18:15:08Z

packages/aws-cdk-lib/aws-s3-deployment/README.md

@@ -362,7 +362,7 @@ new s3deploy.BucketDeployment(this, 'DeployWithSignedPayloads', {

 ## Size Limits

-The default memory limit for the deployment resource is 128MiB. If you need to
+The default memory limit for the deployment resource is 512MiB when the feature flag `@aws-cdk/aws-s3-deployment:defaultMemoryLimit` is enabled, otherwise 128MiB. If you need to


Suggested change

The default memory limit for the deployment resource is 512MiB when the feature flag `@aws-cdk/aws-s3-deployment:defaultMemoryLimit` is enabled, otherwise 128MiB. If you need to

The default memory limit for the deployment resource is 512MiB. If you need to

Let's make it this way as the FF default value is true. We don't need to mention FF in the README.

pahud · 2025-09-16T18:15:35Z

packages/aws-cdk-lib/aws-s3-deployment/lib/bucket-deployment.ts

@@ -154,7 +156,7 @@ export interface BucketDeploymentProps {
   * If you are deploying large files, you will need to increase this number
   * accordingly.
   *
-   * @default 128
+   * @default 512 when feature flag `@aws-cdk/aws-s3-deployment:defaultMemoryLimit` is enabled, otherwise 128


Suggested change

* @default 512 when feature flag `@aws-cdk/aws-s3-deployment:defaultMemoryLimit` is enabled, otherwise 128

* @default 512

pahud · 2025-09-16T18:19:11Z

packages/aws-cdk-lib/recommended-feature-flags.json

@@ -78,5 +78,6 @@
  "@aws-cdk/s3-notifications:addS3TrustKeyPolicyForSnsSubscriptions": true,
  "@aws-cdk/aws-ec2:requirePrivateSubnetsForEgressOnlyInternetGateway": true,
  "@aws-cdk/aws-s3:publicAccessBlockedByDefault": true,
+  "@aws-cdk/aws-s3-deployment:defaultMemoryLimit": true,


@aws-cdk/aws-s3-deployment:defaultMemoryLimit

this is not descriptive for me. How about rename to

@aws-cdk/aws-s3-deployment:default512MemoryLimit ?

And update all occurrences?

- Update BucketDeployment default memory limit from 128MB to 512MB for better S3 sync performance - Add test to verify new default memory behavior - Update documentation to reflect new default - Maintain backward compatibility for explicit memory configurations Fixes aws#35487

- Add @aws-cdk/aws-s3-deployment:defaultMemoryLimit feature flag - When enabled: uses 512MB default memory (performance optimized) - When disabled: uses 128MB default memory (legacy behavior) - Maintains full backward compatibility - Users can still override with explicit memoryLimit values - Addresses PR feedback about breaking changes Closes aws#35487

…test - Add new feature flag to expected defaults in features.test.ts - Feature flag defaults to false (disabled) for backward compatibility - Fixes CI test failure for feature flag defaults validation

@default

- Rename feature flag from 'defaultMemoryLimit' to 'default512MemoryLimit' for clarity - Simplify README documentation to remove feature flag mention since it defaults to true - Simplify JSDoc comment to show '@default 512' without feature flag details - Update all references to use the new feature flag name

…t memory limit - Add explicit MemorySize: 128 property to BucketDeployment Lambda function - This reflects the feature flag implementation that makes memory allocation explicit

- Add @aws-cdk/aws-s3-deployment:configurable-bucket-deployment-memory feature flag - Update BucketDeployment to use feature flag for memory configuration - Maintain backward compatibility with existing behavior - Update integration tests and snapshots

aws-cdk-automation requested a review from a team September 16, 2025 00:21

github-actions bot added beginning-contributor [Pilot] contributed between 0-2 PRs to the CDK bug This issue is a bug. p2 labels Sep 16, 2025

aws-cdk-automation previously requested changes Sep 16, 2025

View reviewed changes

pahud changed the title ~~fix(s3-deployment): increase default memory limit from 128MB to 512MB~~ chore(s3-deployment): increase default memory limit from 128MB to 512MB Sep 16, 2025

pahud self-assigned this Sep 16, 2025

pahud closed this Sep 16, 2025

github-actions bot locked as resolved and limited conversation to collaborators Sep 16, 2025

pahud reopened this Sep 16, 2025

ychjamie requested a deployment to test-pipeline September 16, 2025 05:54 — with GitHub Actions Waiting

ychjamie requested a deployment to test-pipeline September 16, 2025 16:36 — with GitHub Actions Waiting

ychjamie requested a deployment to test-pipeline September 16, 2025 18:01 — with GitHub Actions Waiting

pahud reviewed Sep 16, 2025

View reviewed changes

ychjamie requested a deployment to test-pipeline September 16, 2025 18:57 — with GitHub Actions Waiting

ychjamie force-pushed the fix-35487-bucket-deployment-memory branch from 5dcc65b to 4a99c01 Compare September 17, 2025 00:01

Jamie Yang added 4 commits September 16, 2025 17:16

test(cx-api): add S3_DEPLOYMENT_DEFAULT_MEMORY_LIMIT to feature flag …

53f0324

…test - Add new feature flag to expected defaults in features.test.ts - Feature flag defaults to false (disabled) for backward compatibility - Fixes CI test failure for feature flag defaults validation

ychjamie force-pushed the fix-35487-bucket-deployment-memory branch from 4a06ffc to 9fdf3b5 Compare September 17, 2025 00:16

ychjamie requested a deployment to test-pipeline September 17, 2025 00:17 — with GitHub Actions Waiting

fix(bedrock-alpha): update integration test snapshot for S3 deploymen…

4217b0e

…t memory limit - Add explicit MemorySize: 128 property to BucketDeployment Lambda function - This reflects the feature flag implementation that makes memory allocation explicit

ychjamie requested a deployment to test-pipeline September 17, 2025 04:15 — with GitHub Actions Waiting

ychjamie requested a deployment to test-pipeline September 17, 2025 20:28 — with GitHub Actions Waiting

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chore(s3-deployment): increase default memory limit from 128MB to 512MB #35501

chore(s3-deployment): increase default memory limit from 128MB to 512MB #35501

ychjamie commented Sep 16, 2025 •

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	The default memory limit for the deployment resource is 512MiB when the feature flag `@aws-cdk/aws-s3-deployment:defaultMemoryLimit` is enabled, otherwise 128MiB. If you need to
	The default memory limit for the deployment resource is 512MiB. If you need to

	* @default 512 when feature flag `@aws-cdk/aws-s3-deployment:defaultMemoryLimit` is enabled, otherwise 128
	* @default 512

chore(s3-deployment): increase default memory limit from 128MB to 512MB #35501

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chore(s3-deployment): increase default memory limit from 128MB to 512MB #35501

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Issue # (if applicable)

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Description of changes

Describe any new or updated permissions being added

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ychjamie commented Sep 16, 2025 •

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