Firehose client error with GraalVM about aws-sdk-java-v2 HOT 1 CLOSED

It is working fine in normal traffic, but started to have timeout in high request rate environment.

The error is expected in these conditions, it indicates all connections from the pool were actively being used and the queued requests timed out while awaiting for a connection to become available. The message gives hints on how to mitigate:

Consider taking any of the following actions to mitigate the issue: increase max connections, increase acquire timeout, or slowing the request rate.
Increasing the max connections can increase client throughput (unless the network interface is already fully utilized), but can eventually start to hit operation system limitations on the number of file descriptors used by the process. If you already are fully utilizing your network interface or cannot further increase your connection count, increasing the acquire timeout gives extra time for requests to acquire a connection before timing out. If the connections doesn't free up, the subsequent requests will still timeout.

from aws-sdk-java-v2.