This example shows how to use AWS Lambda SnapStart with the lambda_runtime crate. It implements the [SnapStartResource] trait on an AppState and registers it on the runtime, so the runtime runs the resource's before_snapshot hook before the VM snapshot and its after_restore hook after each restore.

SnapStart reduces cold-start latency by snapshotting the initialized execution environment and restoring from it. Resources created during init (connections, credentials, unique values) may be invalid after restore — before_snapshot / after_restore are where you release and re-establish them. When SnapStart is not enabled, the hooks are never called and the function behaves normally.

SnapStart for functions packaged as OCI images requires a custom base image whose runtime implements the restore lifecycle — which lambda_runtime now does. This example ships a Dockerfile that builds the binary as the Lambda bootstrap on top of public.ecr.aws/lambda/provided:al2023, which supports SnapStart.

Build the image from the repository root (the example depends on the workspace crates via path, so the build context must include them):

docker build -f examples/basic-snapstart/Dockerfile -t basic-snapstart .

Push it to ECR and create the function from the image:

aws ecr create-repository --repository-name basic-snapstart
docker tag basic-snapstart:latest <ACCOUNT>.dkr.ecr.<REGION>.amazonaws.com/basic-snapstart:latest
docker push <ACCOUNT>.dkr.ecr.<REGION>.amazonaws.com/basic-snapstart:latest

aws lambda create-function \
  --function-name basic-snapstart \
  --package-type Image \
  --code ImageUri=<ACCOUNT>.dkr.ecr.<REGION>.amazonaws.com/basic-snapstart:latest \
  --role <YOUR_EXECUTION_ROLE_ARN> \
  --snap-start ApplyOn=PublishedVersions

SnapStart applies to published versions, so publish a version to trigger snapshot creation, then invoke that version (or an alias pointing at it):

aws lambda publish-version --function-name basic-snapstart
aws lambda invoke --function-name basic-snapstart:1 --payload '{"name":"world"}' out.json

The compiled bootstrap is architecture-specific. Build on (or for) the same architecture as the target function — provided:al2023 is available for both x86_64 and arm64.