Query on how envoy utilizes the existing connections or creating a new connection

[sakatkoori]

Need help in understanding when envoy creates a new connection towards upstream or reuse the existing connection.

We have a scenario, where the connection is idle for some random time and when a new request comes to connect to upstream then envoy is reusing the port which belongs to the earlier idle connection then we are seeing the issue istio/istio#38982

So, wanted to understand when will create a new connection towards upstream and when will reuse the connection.

[shreemaan-abhishek]

I'm interested too.

[KBaichoo]

Upstream = collection of endpoints

For a given endpoint, envoy will open a new connection if there's no available connection with capacity for a request. A connection has capacity if it can take a new stream (http request - response) on it. Draining connections are not considering as having capacity.

envoy is reusing the port which belongs to the earlier idle connection then we are seeing the issue

What port is envoy re-using, the source port? It's entirely possible this might be related to having different time_waits between the system(s) communicating.

[sakatkoori]

@KBaichoo Thanks for the response, yes, source port is being reused