[Elastic Agent] Work todo for communication with new Fleet Server

[blakerouse]

Overview

Elastic Agent communication to the new elastic/fleet-server does require some changes to the Fleet gateway code. This is a minimal change that should allow Elastic Agent to communicate with either Kibana or a Fleet Server if done correctly.

Items to do

• Save and send the check-in action token (this is now used to determine what actions the Agent has or has not received)
• Add HTTP2 communication. Agent should now always try to use HTTP2 first, as this provides a performance benefit of having less TCP connections to Fleet Server.

Why

Reduce the TLS load and cloud already support HTTP2, this should be simple addition and it should degrade easily.

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[nchaulet]

@blakerouse I think the agent should know how to talk both to Kibana and Fleet Server if we want to provide the best migration path possible, there is two options here:

• Kibana could support the fleet server API for agent > 7.x
• The agent could know if he is talking to Fleet Server or Kibana (I have a preference for this one, as we do not have a good API versioning strategy on Kibana)

[blakerouse]

@nchaulet I think we can do that without Agent having to worry about which it is talking to.

If we do the following we can remove the need to adjust Agent:

• If when communicating a checkin token is returned then Agent records it and sends it next time. If not its ignored and not sent next time.
• Add the error field to /acks on kibana side (basically just to ignore acks with errors).
• Agent fallsback from HTTP2 to HTTP/1.1 (standard golang stuff)

[elasticmachine]

Pinging @elastic/agent (Team:Agent)

[dikshachauhan-qasource]

Hi @EricDavisX

Cloud you please provide Acceptance criteria for same to validate the ticket.

Thanks
QAS