SSH to servers that have SRV records

ssh-srv

#!/bin/bash
set -o errexit -o nounset -o pipefail
function --help {
cat <<USAGE
 USAGE: ssh-srv <DNS name> <SSH options and args>*

  Allows SSH to nodes referenced by SRV records. The SRV records can be
  referenced in a "plain style":

    service.example.com

  or a "full style":

    _x._y.service.example.com

  If referenced in "plain style", \`ssh-srv\` searches for:

    _*._*.service.example.com

  The hostnames are sorted and deduplicated and then each host is connected to
  in sequence.

USAGE
}

tmp=

function main {
  local failures=() names=() dns="$1" ; shift

  names=( $(lookup "$dns") )

  if [[ ! -t 0 ]]
  then buffer_cmd_stream
  fi

  if [[ ${#names[@]} -le 0 ]]
  then
    echo "No hosts under: $dns" >&2
    exit 2
  fi

  for hostname in "${names[@]}"
  do
    if connect "$hostname" "$@"
    then :
    else
      echo "Non-zero exit ($?) on: $hostname" >&2
      failures+=( "$hostname" )
    fi
  done

  if [[ ${#failures[@]} -gt 0 ]]
  then echo "Non-zero exits: ${failures[@]}" >&2
  fi

  exit ${#failures[@]}
}

function lookup {
  local dns="$1"
  case "$dns" in
    _*._*.*) : ;;                 # Matches _http._tcp and other SRV specifiers
    *)       dns="_*._*.$dns" ;;
  esac
  dig +short "$dns" SRV | cut -d' ' -f4 | sort | uniq | sed 's/[.]$//'
}

function connect {
  if [[ ${#tmp} -gt 0 ]]
  then ssh "$@" < "$tmp"
  else ssh "$@"
  fi
}

function buffer_cmd_stream {
  tmp="/tmp/ssh-srv~$(whoami)/$$.$(token)"
  mkdir -p "$(dirname "$tmp")"
  trap 'rm -rf $tmp' EXIT
  cat > "$tmp"
}

function token {
  printf '%04x' "$RANDOM" "$RANDOM"
}

case "${1:-}" in
  -h|--help) --help ;;
  *)         main "$@" ;;
esac