S3A GET/HEAD requests failing: java.lang.IllegalStateException: Connection is not open/Connection pool shut down

S3 requests failing with an error coming from Http client, "java.lang.IllegalStateException: Connection is not open"

Some online discussion implies that this is related to shared connection pool shutdown & fixed in http client 4.4+. Hadoop & AWS SDK use v 4.5.2 so the fix is in, we just need to make sure the pool is being set up right.

There's a problem here of course: it may require moving to a later version of the AWS SDK, with the consequences on jackson &c, as seen in HADOOP-13050. And that's if there is a patched version out there