[Fleet] Validates the Elastic Version agent on connect.

[ph]

The Agent had a strict version match logic and was refusing to connect to Kibana if the version was not an exact match. (8.0.0 === 8.0.0)

We have removed the logic on the Elastic Agent side and we think that logic should be put into the Fleet side instead that check the User-Agent this will allow better control over the update and how to correctly dispatch the data to the Elastic Agent.

I think the logic should be to refuse the connection if the Elastic-Agent version is higher than the Kibana version.

Reference: elastic/beats#17764

[elasticmachine]

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

[ph]

cc @ruflin WDYT?

[ruflin]

I assume the agent would still have some logic in place (or the processes it runs) to not send data to an Elasticsearch instance older then itself?

For Kibana vs Beats checking it: What are the pros and cons of both options?

I think the more general issue here is that we checked the exact string instead of comparing the minor release? 8.0.1 should work with 8.0.0? Also should 8.0.0 work with 8.0.0-SNAPSHOT? I would assume yes?

[ph]

I assume the agent would still have some logic in place (or the processes it runs) to not send data to an Elasticsearch instance older then itself?

Are you sure we want to do that? I think the idea of doing that is to make sure we have parity of feature like datastream? We should bring it up with platform.

For Kibana vs Beats checking it: What are the pros and cons of both options?

If you do the check on Kibana, you can adapt the response format to the client and have logic in place to better smooth the upgrade/update. We keep the communication open, this gives us a bit more freedom. If you put the hard check on the Elastic Agent, we actually kill the communication channel we can't recover.

8.0.1 should work with 8.0.0? Also should 8.0.0 work with 8.0.0-SNAPSHOT? I would assume yes?

Yes but this check need to happen on the other side using the User Agent string.

[ph]

Work was done in
#75176 and
#76238