Getting com.amazonaws.SdkClientException: Unable to execute HTTP request: Timeout waiting for connection from pool\n\tat Exception

[shanthi-techie]

My download service is downloading files from dell ecs s3 in the rate of 1 request/min (max tps). This service has been running without any issues for months but suddenly its started throwing "com.amazonaws.SdkClientException: Unable to execute HTTP request: Timeout waiting for connection from pool\n\tat Exception".
What i found in my code :

1. I've not closed s3object streams
2. I think its using default connection pool size of 50

But this service has been running for more than 2 months without any issues and approximately it might have processed around 10k documents so far.

S3Object streams are not closed so connections are not returned to pool and its not available to serve further request but how the download service was able to download 10k without any connection pool error.

I've checked heap memory of the application and it has not reached the threshold so GC couldn't have happened i guess.

could someone please shed some light on this ? I guess i miss something very basic here.