HTTP Connection Manager: Add the ability to have per worker stats

[KBaichoo]

HTTP Connection Manager: Add the ability to have per worker stats

Description:

Add stats that will allow us to see imbalance among workers. This is particularly useful for mesh scenarios wherein you might use an exact balance to balance the connection but can still end up with imbalance at the request level.

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Any extra documentation required to understand the issue.

[adisuissa]

I'll let you cc relevant people.

Just thinking out loud here:

This is particularly useful for mesh scenarios wherein you might use an exact balance to balance the connection but can still end up with imbalance at the request level.

In H2 I assume that there may be imbalance at the request level. So adding stats is useful to keep track of things, but not sure if they can be used to change balancing.

[KBaichoo]

Worker imbalance is a bit hard to see, the H2 example that you provide is another case. The reason why this is useful for service mesh is operators might be able to influence the callers compared to say edge use cases.

Anyhow, allowing us to see the imbalance problem can help with figuring out the solution that makes sense in a given case:

• Maybe the solution in some cases is to change how callers call
• Maybe the solution is to limit the max requests per stream lifetime
• Maybe the solution is an endpoint that does GOAWAY to try to rebalance.

cc @alyssawilk @jmarantz