I’m using Heroku mostly for playing around with latest technology and hosting free apps. Since Heroku “changed their pricing model”:http://devcenter.heroku.com/articles/reading-invoice due to the introduction of “the new process model”:http://blog.nofail.de/2011/06/migrating-an-existing-app-to-heroku-celadon-cedar-stack/ some of my apps changed from free to paid, especially those that had some background jobs or nightly crons (I really did not get, why this happend).
h2. Full Stack Background Processes
If you want to run a “resque worker”:http://blog.redistogo.com/2010/07/26/resque-with-redis-to-go/ and a “clockwork process”:http://adam.heroku.com/past/2010/6/30/replace_cron_with_clockwork/ within your web-app, this becomes a costly thing, even if those are just running some minor jobs in the night, because you need to pay for 2 additional dynos.
You could achieve this through defining multiple processes in your Procfile:
# Procfile
web: bundle exec rails server thin -p $PORT
worker: QUEUE=* bundle exec rake environment resque:work
clock: bundle exec clockwork app/clock.rb
heroku scale worker=1 clock=1
h2. Sharing Addon Connections
As Heroku officially announced in their “latest newsletter”:http://newsletterer.heroku.com/2011/07, it’s possible to share connections between multiple apps. In my case, this would be a connection to a redis key-value store, that is provided by “Redistogo”:http://redistogo.com/. It’s as simple as copying the environment configuration for the addon over to the second app:
heroku config | grep DATABASE_URL --app sushi
=> DATABASE_URL => postgres://lswlm...
heroku config:add DATABASE_URL=postgres://lswlm... --app sushi-analytics
=> Adding config vars: DATABASE_URL => postgres://lswlm...m/ldfoiusfsf
=> Restarting app... done, v74.
h2. Going Freemium
So the solution for getting back to a free worker setup is combining 3 Heroku apps and a shared Redis connection through Redistogo:
heroku apps:create freemium-web --stack cedar --remote heroku
git push heroku master
heroku apps:create freemium-worker --stack cedar --remote worker
git push worker master
heroku apps:create freemium-clock --stack cedar --remote clock
git push clock master
heroku scale web=1 --app=freemium-web
heroku scale web=0 worker=1 --app=freemium-worker
heroku scale web=0 clock=1 --app=freemium-clock
heroku addons:add redistogo:nano --app=freemium-web
heroku config:add `heroku config -s --app=freemium-web|grep redis` --app=freemium-worker
heroku config:add `heroku config -s --app=freemium-web|grep redis` --app=freemium-clock
I created an “example project running a Rails 3 application with a mounted Resque web, a Resque worker and a clock process with Clockwork”:https://github.com/phoet/freemium.
h2. Even simpler
If you are just looking for a simple solution of running a background process have a look at “crony, a bootstrap project”:https://github.com/thomasjachmann/crony using “rufus-scheduler”:http://rufus.rubyforge.org/rufus-scheduler/.
If Heroku asks you about billing like this:
$ heroku scale web=0 clock=1 –app=gravity-clock
Scaling clock processes… This action will cause your account to be billed at the end of the month
For more information, see http://docs.heroku.com/billing
Are you sure you want to do this? (y/n) n
Try setting all to 0 first:
$ heroku scale web=0 worker=0 clock=0 –app=gravity-clock
Scaling clock processes… done, now running 0
Scaling web processes… done, now running 0
Scaling worker processes… done, now running 0
then:
$ heroku scale web=0 worker=0 clock=1 –app=gravity-clock
Scaling clock processes… done, now running 1
Scaling web processes… done, now running 0
Scaling worker processes… done, now running 0
Enjoy! =)
Alvin Lai
awesome
Have you ever tried to do this with Heroku scaler? It would be kinda awesome, but I still haven’t got there… :/
If your cron jobs are short running than the heroku scheduler could be a solution for you: https://devcenter.heroku.com/articles/scheduler.
That will be charged by hour.
I tried that already. But my rake task was to big (long time running) and the scheduler canceled the job :-)
unfortunately this is agains heroku tos :/
http://policy.heroku.com/tos 4.4:
“You may not develop multiple Applications to simulate or act as a single Application or otherwise access the Heroku Services in a manner intended to avoid incurring fees.”
Check out https://github.com/mperham/girl_friday in-process background processing, so no worker is needed.
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