Add a knob to make per_connection_buffer_limit_bytes of cluster configurable

[aoledk]

Description:

EG can configure per_connection_buffer_limit_bytes on xDS Listener currently via #2600, not available to configure per_connection_buffer_limit_bytes on xDS Cluster, default to 32KB. A new knob will be better for entire buffer sizing control of Envoy provisioned by EG.

[optional Relevant Links:]

https://gateway.envoyproxy.io/latest/api/extension_types/#connection https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/cluster/v3/cluster.proto#config-cluster-v3-cluster

[ShyunnY]

hey, @aoledk Do you have any ideas or are you currently working on this PR?

[aoledk]

hey, @aoledk Do you have any ideas or are you currently working on this PR?

@ShyunnY Perhaps this feature should be implemented via BackendTrafficPolicy, similar way like https://gateway.envoyproxy.io/latest/api/extension_types/#connection works. And I'm not working on this Issue.

[ShyunnY]

/assign

[guydc]

+1 in general. @aoledk - can you maybe describe the scenario where this is needed?

[aoledk]

@guydc When EG is used as L4 proxy and serves massive long lived TCP connection, the buffer size of <Downstream, Envoy> and <Envoy, Upstream> connections should be controlled, to reduce memory consumption of Envoy.