Re-using SSH connections with controlmaster (Misc)
Running multiple seperate commands via seperate SSH invocations can be very slow, so we sometimes want to multiplex SSH sessions over an existing connection (i.e. re-use the connection).
This can be particularly useful if you're shelling into a system which requires two-factor authentication as you'll only need to answer a challenge for the first connection.
It's also useful if you're using something like ansible, as it can massively improve runbook speed.
Details
- Language: Misc
Snippet
# The original set of commands
# There's going to be 3 connections, handshakes etc and it'll be slow to run
ssh $dest "uname -r"
ssh $dest "docker ps -q | wc -l"
ssh $dest "ls /some/dir/ | wc -l"
# Instead, open a control connection
ssh -o controlmaster=auto -o controlpath=~/.ssh/.ssh-%r@%h:%p -N $dest &
# Get piddy mcpidface
control_pid=$!
# do the other SSH stuff as before, but give it the controlmaster details
ssh -o controlmaster=auto -o controlpath=~/.ssh/ssh-%r@%h:%p $dest "uname -r"
ssh -o controlmaster=auto -o controlpath=~/.ssh/.ssh-%r@%h:%p $dest "docker ps -q | wc -l"
ssh -o controlmaster=auto -o controlpath=~/.ssh/.ssh-%r@%h:%p $dest "ls /influxdb/meta/ | wc -l"
# Once we're done, tidy up the original connection
kill $control_pid
# Done
# -----------------------------
# If we wanted to make this behaviour the default
# put this into ~/.ssh/config
#
host *
controlmaster auto
controlpath ~/.ssh/.ssh-%r@%h:%p