Execute multiple commands re-using same ssh connection - bash

Question

I need to ssh into memcached servers and execute ensure connectivity.
I am supposed to re-use the same ssh connection and keep executing the commands whose output will be stored in some log. This is supposed to be a scheduled job which runs at some specific intervals.
Code 1 makes multiple ssh connections for each execution.
#!/bin/bash
USERNAME=ec2-user
HOSTS="10.243.107.xx 10.243.124.xx"
KEY=/home/xxx/xxx.pem
SCRIPT="echo stats | nc localhost 11211 | grep cmd_flush"
for HOSTNAME in ${HOSTS} ; do
ssh -l ${USERNAME} -i ${KEY} ${HOSTNAME} "${SCRIPT}"
done
Code 2 hangs after ssh.
#!/bin/bash
USERNAME=ec2-user
KEY=/home/xxx/xxx.pem
ssh -l ${USERNAME} -i ${KEY} 10.243.xx.xx
while:
do
echo stats | nc localhost 11211 | grep cmd_flush
sleep 1
done
Is there any better way of doing this?

Answer 1

Since you want to have Code 2 run the infinite while loop on the remote host, you can pass that whole thing to the ssh command, after fixing the while statement:
#!/bin/bash
USERNAME=ec2-user
KEY=/home/xxx/xxx.pem
ssh -l ${USERNAME} -i ${KEY} 10.243.xx.xx '
while true
do
echo stats | nc localhost 11211 | grep cmd_flush
sleep 1
done
'
I have to warn that I think the whole approach is somewhat fragile, though. Long-standing ssh connections tend to die for various reasons, which don't always mean the connectivity is actually broken. Make sure the parent script that calls this notices dropped ssh connections and tries again. I guess you can put this script in a loop, and maybe log a warning each time the connection is dropped, and log an error if the connection cannot be re-established.