Add recommendations for keeping connections alive

[tigrannajaryan]

1. Intermediaries such as load balancers may time out inactive connections. Add recommendations on how to keep it alive (either use WebSocket ping/pong or send empty status report).
2. Explain how clients should react to disconnections. Do they re-connection immediately? When do they pause (throttling) before re-connecting?

[djaglowski]

1. Intermediaries such as load balancers may time out inactive connections. Add recommendations on how to keep it alive (either use WebSocket ping/pong or send empty status report).

Related, the server should probably be able to specify a frequency for keep alive signals. This would allow it to adjust based on the networking environment.

2. Explain how clients should react to disconnections. Do they re-connection immediately? When do they pause (throttling) before re-connecting?

I think we can assume there are scenarios where the client repeatedly either 1) fails to connect or 2) connects but loses it after only a moment, not long enough to receive instructions from the server. In either case, the client should probably backoff based on rate of connection attempts. I'm not sure the exact algorithm need be part of the spec, but it seems reasonable to suggest that there should be one.

[tigrannajaryan]

Related, the server should probably be able to specify a frequency for keep alive signals. This would allow it to adjust based on the networking environment.

If we want this then it can be a field in ConnectionSettings message.

[tigrannajaryan]

#36 should solve part of the problems. We may still need to add ability to instruct the Agent how often to ping/pong or send status reports to avoid disconnection due to idle timeout, so I will keep this open to address that.

[haoqixu]

This issue appears to be resolved by #190.