wait_for_ssh

#!/bin/bash

help() {
   echo 'usage: wait_for_ssh HOST [PORT]'
   echo '       wait_for_ssh --help'
   echo
   echo '    Loops trying to connect via ssh until it succeeds'
   echo
   exit 1
}

[ "$1" == "--help" ] && help
[ "$1" == ""       ] && help
HOST="$1"
if [ "$2" == "" ]; then
  PORT=
else
  PORT="$2"
fi

set -u          # stop on undefined variable
set -o pipefail # stop part of pipeline failing

SLEEP=5 # seconds
ssh_status=down

log() {
  echo "$( date --rfc-3339=ns ): $1" >&2
}

while [ "$ssh_status" == "down" ]; do
  log "trying to connect"
  if [ "$PORT" == "" ]; then
    ssh $HOST true
  else
    ssh $HOST -p $PORT true
  fi
  if [ "$?" != "0" ]; then
    log "failed. Sleeping for ${SLEEP}s"
    sleep $SLEEP
  else
    log "connected successfully"
    break
  fi
done