A simple wrapper around `git push heroku` to gracefully handle when you have migrations to run.

heroku_deploy.rb

#!/bin/sh -e
# ------------------------------------------------------------------
# Phil Oye
# heroku_deploy
# A simple wrapper around `git push heroku` to gracefully handle
# when you have migrations to run.
#
# ------------------------------------------------------------------
# HOW IT WORKS
#
# If there are no migrations, then push per usual.
#
# If there ARE migrations to run, then:
#    1. Backup database
#         * only if remote is named 'production'
#         * make sure you have pg_backups enabled.
#    2. Turn on maintenance mode
#    3. Power down workers
#    4. Push 
#    5. Run migrations
#    6. Power up workers
#    7. Retart app
#    8. Turn off maintenance mode
# 
# If -u <url> is passed, then that URL will be pinged to warm up 
# the application.
#
# ------------------------------------------------------------------
# MIT LICENSED
# Copyright (c) 2014 Phil Oye

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
# ------------------------------------------------------------------

PROGNAME=${0##*/}
VERSION=0.1

function usage {
  echo "usage: heroku_deploy [-hv] [-a appname ] [-r gitremote] [-u pingurl]"
}

function help_message {
  echo "
  $PROGNAME v$VERSION — A wrapper around git push heroku

  $(usage)

  -a <app>     required  Heroku application name
  -r <remote>  optional  Git remote to push to
                         default is heroku
                         Suggest renaming remotes to match environment
                         Only remote named production will backup database
                         before running migrations
  -u <url>     optional  Ping this URL after deployment to warm up the app
                         and ensure the site is up
  -q           optional  Suppress log messages from this script
                         heroku's git push output will remain
  -h           optional  Print this help message
  -v           optional  Print version
  "
  exit 1
}

if [ $# == 0 ] ; then
  help_message
  exit 1
fi

function logit () {
  if [[ $QUIET != "true" ]]; then
    echo $1
  fi
}

function exit_with_error () {
  logit "$1"
  exit 1
}

# set defaults
REMOTE=heroku

while getopts :hqva:r:u: args; do
  case $args in
    h) help_message ;;
    q) QUIET='true' ;;
    v) echo "$PROGNAME version $VERSION"; exit ;;
    a) APP_NAME="$OPTARG" ;;
    r) REMOTE="$OPTARG" ;;
    u) PING_URL="$OPTARG" ;;
    :) echo "No value for option -$OPTARG."; usage; exit 1 ;;
   \?) echo "Unknown option -$OPTARG."; usage; exit 1 ;;
  esac
done
shift $(($OPTIND - 1))

function main {

  COMMITS_TO_DEPLOY=$(git rev-list --count master...$REMOTE/master)
  if [ "$COMMITS_TO_DEPLOY" = "0" ]; then
    exit_with_error "Nothing to deploy to $REMOTE."
  fi

  logit "About to deploy $COMMITS_TO_DEPLOY commits to $REMOTE."

  MIGRATIONS=$(git diff HEAD $REMOTE/master --name-only -- db | wc -l)

  # migrations require downtime so enter maintenance mode
  if test $MIGRATIONS -gt 0; then
    logit "There are $MIGRATIONS DB migrations to run."

    if [ "$REMOTE" = "production" ]; then
      logit "Backing up the $REMOTE database."
      heroku pgbackups:capture --expire
    else
      logit "Skipping database backup on $REMOTE."
    fi

    logit "Turning on maintenance mode."
    PREV_WORKERS=$(heroku ps --app $APP_NAME | grep "^worker." | wc -l | tr -d ' ')
    heroku maintenance:on --app $APP_NAME

    # Make sure workers are not running during a migration
    logit "Turning off $PREV_WORKERS workers."
    heroku scale worker=0 --app $APP_NAME
  else
    logit "No DB migrations to run, so skipping maintenance mode."
  fi

  logit "Pushing to $REMOTE."
  git push $REMOTE

  # run database migrations if needed and restart background workers once finished
  if test $MIGRATIONS -gt 0; then
    logit 'Running migrations...'
    heroku run rake db:migrate db:seed --app $APP_NAME
    logit "Scaling back up to $PREV_WORKERS workers."
    heroku scale worker=$PREV_WORKERS --app $APP_NAME
    logit 'Restarting application.'
    heroku restart --app $APP_NAME
  fi

  # echo 'Clearing the cache.'
  # rake cache:clear

  if test $MIGRATIONS -gt 0; then
    logit 'Turning off maintenance mode.'
    heroku maintenance:off --app $APP_NAME
  fi
  logit "Deployed to $REMOTE."

  if [ "$REMOTE" = "production" ] && [ "$PING_URL" != '' ]; then
    SLEEP_TIME=3
    logit "Let's make sure the site is up, and warm up the site in the process."
    logit "First, sleep for $SLEEP_TIME seconds..."
    sleep $SLEEP_TIME
    logit "Ok, let's hit $PING_URL."
    CODE=$(curl -sL -w "%{http_code}\\n" "$PING_URL" -o /dev/null)
    if [ "$CODE" = "200" ]; then
      logit "$PING_URL successfully returned a $CODE."
    else
      logit "$PING_URL returned a $CODE."
      exit 2
    fi
  fi

}

main "$@"