[jira] [Created] (MESOS-7569) Allow "old" executors with half-open connections to be preserved during agent upgrade / restart.

["Benjamin Mahler (JIRA)" <ji...@apache.org>]

Benjamin Mahler created MESOS-7569:
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             Summary: Allow "old" executors with half-open connections to be preserved during agent upgrade / restart.
                 Key: MESOS-7569
                 URL: https://issues.apache.org/jira/browse/MESOS-7569
             Project: Mesos
          Issue Type: Bug
          Components: agent
            Reporter: Benjamin Mahler


Users who have executors in their cluster without the fix to MESOS-7057 will experience these executors potentially being destroyed whenever the agent restarts (or is upgraded).

This occurs when these old executors have connections idle for > 5 days (default conntrack tcp timeout). At this point, the connection is timedout and no longer tracked by conntrack. From what we've seen, if the agent stays up, the packets still flow between the executor and agent. However, once the agent restarts, in some cases (presence of a DROP rule, or some flavors of NATing), the executor does not receive the RST/FIN from the kernel and will hold a half-open TCP connection. At this point, when the executor responds to the reconnect message from the restarted agent, it's half-open TCP connection closes, and the executor will be destroyed by the agent.

In order to allow users to preserve the tasks running in these "old" executors (i.e. without the MESOS-7057 fix), we can add *optional* retrying of the reconnect message in the agent. This allows the old executor to correctly establish a link to agent, when the second reconnect message is handled.

Longer term, heartbeating or TCP keepalives will prevent the connections from reaching the conntrack timeout (see MESOS-7568).



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