abhishek-chouhan opened a new issue, #14090:
URL: https://github.com/apache/druid/issues/14090

   Currently DruidLeaderClient invalidates the cache when it encounters an 
IOException or a ChannelException 
([here](https://github.com/apache/druid/blob/master/server/src/main/java/org/apache/druid/discovery/DruidLeaderClient.java#L160)).
 In environments where proxies/sidecars are involved in communication between 
Druid components, there is also the possibility of getting errors from the 
proxy itself such as a 503, when the requested endpoint for outbound 
communication is unavailable.
   In this case DruidLeaderClient treats 503 as a valid response and propogates 
it back to the caller, even if the caller retries, the internal cache is never 
refreshed and the requested node is not re-resolved. This leads to continuous 
failures for scenarios such as rolling restarts/upgrades when the cache needs 
to be re-resolved.
   One of the options of dealing with this is to extend the API and allow 
callers to pass in the HTTP responses which they want to handle. If we get a 
response with any of these, we pass it onwards to the caller, for anything else 
we do a best-effort retry inside the DruidLeaderClient (similar to IOException) 
by clearing the cache, which if its still unsuccessful is returned to the 
caller to deal with(existing behavior).


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