CircleCIでherokuのprebootの設定を自動で行う ref: http://qiita.com/nafu/items/4c480934871bbdfb56e9

circle.yml

deployment:
  production:
    branch: master
    commands:
      - NEED_MAINTENANCE_MODE=`./script/circleci.sh`; if [ $NEED_MAINTENANCE_MODE -eq 1 ]; then heroku features:disable preboot --app production; else heroku features:enable preboot --app production; fi
      - NEED_MAINTENANCE_MODE=`./script/circleci.sh`; if [ $NEED_MAINTENANCE_MODE -eq 1 ]; then heroku maintenance:on --app production; fi
      - NEED_MAINTENANCE_MODE=`./script/circleci.sh`; if [ $NEED_MAINTENANCE_MODE -eq 1 ]; then heroku scale worker=0 --app production; fi
      - git push -f git@heroku.com:production.git $CIRCLE_SHA1:refs/heads/master
      - NEED_MAINTENANCE_MODE=`./script/circleci.sh`; if [ $NEED_MAINTENANCE_MODE -eq 1 ]; then heroku run 'rake db:migrate' --app production; fi
      - heroku run 'rake db:seed' --app production
      - NEED_MAINTENANCE_MODE=`./script/circleci.sh`; if [ $NEED_MAINTENANCE_MODE -eq 1 ]; then heroku maintenance:off --app production; fi
      - NEED_MAINTENANCE_MODE=`./script/circleci.sh`; if [ $NEED_MAINTENANCE_MODE -eq 1 ]; then heroku features:enable preboot --app production; fi

circleci.sh

#!/bin/bash

# get compare SHA1
compare_url=$CIRCLE_COMPARE_URL
compare_ids=${compare_url#*compare/}

# set NEED_MAINTENANCE_MODE if schema.rb is changed
if git diff --name-only $compare_ids | grep -q 'schema.rb'; then
  echo 1
else
  echo 0
fi