listener: support keepalive configuration

[jronak]

Commit Message: This change introduces the ability to configure TCP keepalive settings on additional listener addresses. Currently users have to set the corresponding socket options directly and with this change users can enable TCP keepalive for both primary and additional addresses via the listener configuration similar to the cluster configuration.

Additional Description: Configuration example:

static_resources:
  listeners:
  - name: "listener"
    address:
      socket_address:
        address: 127.0.0.1
        port_value: 10000
    # TCP keepalive configuration for the primary address.
    tcp_keepalive:
      keepalive_time: 60000       # time in milliseconds before probing starts
      keepalive_interval: 10000   # interval between probes in milliseconds
      keepalive_probes: 5         # number of abandoned probes before closing connection
    additional_addresses:
      - address:
          socket_address:
            address: 127.0.0.2
            port_value: 10001
        # TCP keepalive configuration for the additional address.
        tcp_keepalive:
          keepalive_time: 60000
          keepalive_interval: 10000
          keepalive_probes: 5

Risk Level: low
Testing: unit and integration
Docs Changes: NA
Release Notes: NA

[repokitteh-read-only]

CC @envoyproxy/api-shepherds: Your approval is needed for changes made to (api/envoy/|docs/root/api-docs/).
envoyproxy/api-shepherds assignee is @adisuissa
CC @envoyproxy/api-watchers: FYI only for changes made to (api/envoy/|docs/root/api-docs/).

🐱

Caused by: #38467 was opened by jronak.

see: more, trace.

[adisuissa]

High-level comment:
prior to additional-addresses, the listener to address 1-1 mapping introduced some address related config knobs in the listener.
I think that in order to ensure that a coherent config design is used, the fields in the listener level will impact all the addresses (both the primary and additional), and the additional address will be able to override the config (just as being done for socket options).
I also think that it would be better to have a common-address-options (similar to UpstreamConnectionOptions) that can be used to optionally override these values.

[adisuissa]

/wait

[jronak]

Thanks for the comments @adisuissa

prior to additional-addresses, the listener to address 1-1 mapping introduced some address related config knobs in the listener.
I think that in order to ensure that a coherent config design is used, the fields in the listener level will impact all the addresses (both the primary and additional), and the additional address will be able to override the config (just as being done for socket options).

Updated the PR to use apply keepalive configuration across all the additional addresses and ability override/disable keepalive at each additional address level.

I also think that it would be better to have a common-address-options (similar to UpstreamConnectionOptions) that can be used to optionally override these values.

Happy to update the PR to use common address options, am I understanding the definition correctly?

message AddressOptions {
  core.v3.TcpKeepalive tcp_keepalive ;
}

message AdditionalAddress {
  ...
  AddressOptions address_options_override;
}

message Listener {
  ...
  AddressOptions common_address_options;
} 

What about socket_options field?