Enable WEB_CONCURRENCY to be set to a default value based on dyno size

Change effective on 02 March 2015

The feature described below is not recommended. The SENSIBLE_DEFAULTS environment variable was never stabilized and is not documented for public use other than this changelog article. We recommend using dyno load to tune your application’s process count instead.

If a Ruby application has the configuration variable SENSIBLE_DEFAULTS set, then the configuration variable WEB_CONCURRENCY will be defaulted to a value based on the dyno size.

When enabled the value will default to:

  • 1X dynos: WEB_CONCURRENCY=2
  • 2X dynos: WEB_CONCURRENCY=4
  • PX dynos: WEB_CONCURRENCY=16

If WEB_CONCURRENCY is manually set, this functionality will be disabled.

You must deploy after setting SENSIBLE_DEFAULTS to activate this functionality.

$ heroku config:set SENSIBLE_DEFAULTS=enabled
$ git commit --allow-empty -m "enable sensible defaults"
$ git push heroku master
$ heroku run bash --size 2X
Running `bash` attached to terminal... up, run.7530

Optimizing dyno usage docs