Using SnapStart for .NET8 throws InvalidStateTransition

[tmitchel2]

I've updated a lambda function to use .NET8 runtime (instead of a custom container) to take advantage of the new SnapStart feature. My function is invoked via ApiGateway. The function works perfectly fine with all these changes and SnapStart disabled. However, when I enable SnapStart the invocation always fails with the following:

2024-11-20T15:03:02.885Z		fail	Failed to invoke before snapshot hooks: HTTP Response: 
{
    "errorMessage": "State transition from Running to Ready failed for runtime. Error: State transition is not allowed",
    "errorType": "InvalidStateTransition"
}
Amazon.Lambda.RuntimeSupport.RuntimeApiClientException`1[Amazon.Lambda.RuntimeSupport.ErrorResponse]: Forbidden
Status: 403
Response: 
{
    "errorMessage": "State transition from Running to Ready failed for runtime. Error: State transition is not allowed",
    "errorType": "InvalidStateTransition"
}
   at Amazon.Lambda.RuntimeSupport.InternalRuntimeApiClient.NextAsync(String endpointUrl, CancellationToken cancellationToken) in /src/Repo/Libraries/src/Amazon.Lambda.RuntimeSupport/Client/InternalClientAdapted.cs:line 302
   at Amazon.Lambda.RuntimeSupport.RuntimeApiClient.RestoreNextInvocationAsync(CancellationToken cancellationToken) in /src/Repo/Libraries/src/Amazon.Lambda.RuntimeSupport/Client/RuntimeApiClient.cs:line 155
   at Amazon.Lambda.RuntimeSupport.Helpers.SnapstartHelperInitializeWithSnapstartIsolatedAsync.InitializeWithSnapstartAsync(IRuntimeApiClient client, Object restoreHooksRegistry) in /src/Repo/Libraries/src/Amazon.Lambda.RuntimeSupport/Helpers/SnapstartHelperInitializeWithSnapstartIsolatedAsync.cs:line 29

So essentially its running my custom code in RegisterBeforeSnapshot and then fails immediately after.

Im interested to know if anyone can suggest a path to approach solving this issue? if indeed it is something Im doing incorrectly...

[Beau-Gosse-dev]

We'll look into this and may request more info.

[bhallasaksham]

Few more questions -

• How are you enabling SnapStart? Are you manually setting any environment variables?
• Are you using NativeAOT?

[bhallasaksham]

Seems like the BeforeSnapshot hooks are running during the RESTORE phase, and not during INIT phase?

[tmitchel2]

I turned bootstrap logging on and it's made me understand the process a lot more and given me a direction.

I think the confusion arises because I'm using minimal API style / nativeaot compatible approach (but obviously not turned on for this particular deployment). The documentation for snap start is thin for minimal API from what I can see and I assumed that the hooks should be wired up before the RunAsync, but for this approach that is wrong, it should be in the constructor. Seeing the snapshot hooks getting fired also threw me off considering it was restored already.

Anyway I will play around with it again and refer back once I have it working.

[tmitchel2]

Ok so I've resolved the issue, the LAMBDA_RUNTIMESUPPORT_DEBUG was very helpful so I appreciate you pointing that out to me.

My issue arose because I was using a Executable Assembly style but my cdk handler was configured for Class Library approach. Interestingly that still worked with snapstart disabled and thats what caused the confusion. When SnapStart was enabled, it would take over and it would search for a constructor that wasnt there in the LambdaEntryPoint, and thus wouldnt register the hooks and wouldnt run any of my code.

TLDR I made some other changes, but the main fix for me was to update my handler to the execution assembly style:

handler: "Destash.Server"