juju ssh gives i/o timeout if latency is more than 500ms

[Vidar Tyldum]

We have a remote site with an RTT of about 580ms, and "juju ssh" will fail with an i/o timeout during the host key checking phase.

50:09 DEBUG juju.network.ssh reachable.go:156 dialing 111.111.173.32:22 to check host keys
09:50:09 DEBUG juju.network.ssh reachable.go:156 dialing 111.111.171.186:22 to check host keys
09:50:10 DEBUG juju.network.ssh reachable.go:159 dial 111.111.173.32:22 failed with: dial tcp 10.104.173.32:22: i/o timeout
09:50:10 DEBUG juju.network.ssh reachable.go:159 dial 111.111.171.186:22 failed with: dial tcp 10.104.171.186:22: i/o timeout

I could reproduce this by simulating the latency with tc:
  sudo tc qdisc add dev ens3 root netem delay 510ms

[Vidar Tyldum (tyldum)]

Just confirming that this patch works (up to 1 second RTT) for juju v2.9:
https://github.com/tyldum/juju/commit/df22134ddc360fd95bffff5b9cb0fe2c58a8caba

[Erlon R. Cruz (sombrafam)]

Hi folks,

I have created a pull request to implement this fix: https://github.com/juju/juju/pull/16140