如何使用 SnapStart 将 CRaC 运行时挂钩附加到 AWS Lambda？

Question

I tried to follow the instructions from the online docs exactly, and I even included the System.identityHashCode(this) on each line to make sure it was the same object and wasn't being garbage collected:

public class MyLambdaHandler extends AppConfigHelper implements RequestStreamHandler, Resource {
    public MyLambdaHandler() {
        System.out.println("Constructor called: " + System.identityHashCode(this));
        Core.getGlobalContext().register(this);
    }
    @Override
    public void beforeCheckpoint(org.crac.Context<? extends Resource> context) throws Exception {
        System.out.println("Before checkpoint: " + System.identityHashCode(this));
    }
    @Override
    public void afterRestore(org.crac.Context<? extends Resource> context) throws Exception {
        System.out.println("After restore: " + System.identityHashCode(this));
    }
    @Override
    public void handleRequest(final InputStream input, final OutputStream output, final Context context) throws IOException {
        System.out.println("Request handler called: " + System.identityHashCode(this));
    }
}

But on the first invocation, you can see that neither the beforeCheckpoint() or afterRestore() are getting called:

Constructor called: 91912419
START RequestId: b56b282f-4712-4d18-b300-f6e031c9468a Version: $LATEST
Request handler called: 91912419
END RequestId: b56b282f-4712-4d18-b300-f6e031c9468a
REPORT RequestId: b56b282f-4712-4d18-b300-f6e031c9468a  Duration: 173.24 ms Billed Duration: 174 ms Memory Size: 1024 MB    Max Memory Used: 196 MB Init Duration: 2084.86 ms   

On the second invocation, you can see the same object 91912419 is being reused, but again neither of the runtime hooks are being called:

START RequestId: b1ca407e-725c-4c17-93aa-46251f1c65a6 Version: $LATEST
Request handler called: 91912419
END RequestId: b1ca407e-725c-4c17-93aa-46251f1c65a6
REPORT RequestId: b1ca407e-725c-4c17-93aa-46251f1c65a6  Duration: 1.58 ms   Billed Duration: 2 ms   Memory Size: 1024 MB    Max Memory Used: 195 MB 

Answer 1

You need to manually publish a version for SnapStart to work, you can't use SnapStart on $LATEST . From the docs ( https://docs.aws.amazon.com/lambda/latest/dg/snapstart.html#snapstart-runtimes ):

You can use SnapStart only on published function versions and aliases that point to versions. You can't use SnapStart on a function's unpublished version ($LATEST).