NIFI-15535 - Fixed AWS Connection Pool Shutdown on EKS with STS Credential Refresh

[pvillard31]

Summary

NIFI-15535 - Fixed AWS Connection Pool Shutdown on EKS with STS Credential Refresh

Fixed java.lang.IllegalStateException: Connection pool shut down affecting AWS processors (SQS, S3, etc.) on EKS with pod-level identity. The issue occurs when STS temporary credentials expire and the internal HTTP connection pool used for credential refresh has been garbage collected by the JVM Finalizer thread.

The AWSCredentialsProviderControllerService cached a single AwsCredentialsProvider instance created during @OnEnabled. On EKS, this resolves to a DefaultCredentialsProvider whose internal chain creates an StsClient with its own ApacheHttpClient and PoolingHttpClientConnectionManager. The JVM's Finalizer thread can shut down these internal connection pools (confirmed in logs by [Finalizer] Connection manager is shutting down entries). While cached STS credentials remain valid (~1h), requests succeed. Once credentials expire, the STS refresh call fails because its HTTP pool was already shut down.

This is a documented AWS SDK V2 behavior: https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/troubleshooting.html#faq-connection-pool-shutdown-exception

The prior fix for NIFI-12836 (commit 02cbe199260) changed DefaultCredentialsProvider.create() to .builder().build() to avoid the singleton, but the provider was still cached as a single shared instance in the controller service, leaving it vulnerable to GC finalization of internal SDK objects.

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[turcsanyip]

Thanks @pvillard31 for the PR. The fix looks fine on a cursory review. Will check it in more detail and run some tests before merging.