eolivelli opened a new pull request, #19661:
URL: https://github.com/apache/pulsar/pull/19661

   ### Motivation
   
   There is a race condition while creating a Connection and putting it into 
the cache.
   The operation may fail before that the CompletableFuture is put into the 
pool map and so cleanupConnection fails to remove the new connection from the 
map (because it is not there yet)
   
   
   This is very likely to happen on k8s while a broker is not "ready"
   The problem is that UnknownHostException fails very quickly (probably on the 
same thread), and the "exceptionally" block is executed before we put the 
CompletableFuture into the `pool` map, and so the "remove" operation fails
   
   
   ### Modifications
   
   Eagerly remove the CompletableFuture from the cache if it is "failed".
   There is no need to retry, the client eventually will retry, and also 
retrying immediately will probably fail.
   
   ### Verifying this change
   
   I am not adding tests, this race condition is hard to reproduce. But it 
happens sometimes on some k8s clusters during fault injection tests.
   
   ### Does this pull request potentially affect one of the following parts:
   
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   - [ ] Dependencies (add or upgrade a dependency)
   - [ ] The public API
   - [ ] The schema
   - [ ] The default values of configurations
   - [ ] The threading model
   - [ ] The binary protocol
   - [ ] The REST endpoints
   - [ ] The admin CLI options
   - [ ] The metrics
   - [ ] Anything that affects deployment
   
   ### Documentation
   
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   - [ ] `doc` <!-- Your PR contains doc changes. -->
   - [ ] `doc-required` <!-- Your PR changes impact docs and you will update 
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   - [x] `doc-not-needed` <!-- Your PR changes do not impact docs -->
   - [ ] `doc-complete` <!-- Docs have been already added -->
   
   ### Matching PR in forked repository
   
   PR in forked repository: <!-- ENTER URL HERE -->
   
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