Simple systemd upgrade proof-of-concept

upgrade-test.sh

#!/bin/bash
#
# This script can be daemonized by systemd and shows how to do an in-place upgrade
# with service type=fork and pid files. If you watch systemctl status, you will see
# that the PID and command line of the service update after 20 seconds to reflect
# the script executed with 'type=upgraded-child'. After 5 minutes, the service will
# stop itself.
#
# upgrade-test.service:
#
# [Unit]
# Description=In-place upgrade test
# 
# [Service]
# Type=forking
# PIDFile=/run/upgrade-test.pid
# ExecStart=/bin/bash /root/upgrade-test.sh --type=daemon --pid-file=/run/upgrade-test.pid
#

SELF="${BASH_SOURCE[0]}"

PARSED=$(getopt -o '' --longoptions="type:,pid-file:" --name "$0" -- "$@")
if (( $? != 0 )); then
  echo "Failed to parse command line"
  exit 2
fi

eval set -- "$PARSED"

while true; do
  case "$1" in
    --type)
      TYPE="$2"
      shift 2
      ;;
    --pid-file)
      PID_FILE="$2"
      shift 2
      ;;
    --)
      shift
      break
      ;;
    *)
      echo "Unprocessed option: $1"
      exit 3
      ;;
  esac
done

if [[ -z "$PID_FILE" ]]; then
  echo "Missing required option: --pid-file"
  exit 2
fi

case "$TYPE" in
  daemon)
    # Systemd expects a forking process to, well, fork...
    "$SELF" --type=child --pid-file="$PID_FILE" &
    echo $! > "$PID_FILE"
    disown
    exit 0
    ;;
  child)
    # Simulate process doing some work
    sleep 10
    "$SELF" --type=upgraded-child --pid-file="$PID_FILE" &
    CHILD_PID=$!
    # Simulate process cleaning up resources
    # You'll see during this time that systemd knows of both instances
    # of the script, and still treats this instance as the main one.
    sleep 10
    echo $CHILD_PID > "$PID_FILE"
    disown
    exit 0
    ;;
  upgraded-child)
    sleep 300
    exit 0
    ;;
  *)
    echo "Unrecognized type: $TYPE"
    exit 2
    ;;
esac