zulip/puppet/zulip_ops/files/nagios_ssh_config

Host *
  ControlMaster no
  ControlPath /tmp/ssh-%C

  ServerAliveInterval 30
  ServerAliveCountMax 3
puppet: Use existing autossh tunnels as OpenSSH "master" sockets. A number of autossh connections are already left open for port-forwarding Munin ports; autossh starts the connections and ensures that they are automatically restarted if they are severed. However, this represents a missed opportunity. Nagios's monitoring uses a large number of SSH connections to the remote hosts to run commands on them; each of these connections requires doing a complete SSH handshake and authentication, which can have non-trivial network latency, particularly for hosts which may be located far away, in a network topology sense (up to 1s for a no-op command!). Use OpenSSH's ability to multiplex multiple connections over a single socket, to reuse the already-established connection. We leave an explicit `ControlMaster no` in the general configuration, and not `auto`, as we do not wish any of the short-lived Nagios connections to get promoted to being a control socket if the autossh is not running for some reason. We enable protocol-level keepalives, to give a better chance of the socket being kept open. 2022-11-01 20:04:16 +01:00			`Host *`
			`ControlMaster no`
			`ControlPath /tmp/ssh-%C`

			`ServerAliveInterval 30`
			`ServerAliveCountMax 3`