How can I detect Heroku's environment?

Question

I have a Django webapp, and I\'d like to check if it\'s running on the Heroku stack (for conditional enabling of debugging, etc.) Is there any simple way to do this? An envi

Answer 1

Similar to what Neil suggested, I would do the following:

debug = True
if 'SOME_ENV_VAR' in os.environ:
    debug = False

I've seen some people use if 'PORT' in os.environ: But the unfortunate thing is that the PORT variable is present when you run foreman start locally, so there is no way to distinguish between local testing with foreman and deployment on Heroku.

I'd also recommend using one of the env vars that:

1. Heroku has out of the box (rather than setting and checking for your own)
2. is unlikely to be found in your local environment

At the date of posting, Heroku has the following environ variables:

['PATH', 'PS1', 'COLUMNS', 'TERM', 'PORT', 'LINES', 'LANG', 'SHLVL', 'LIBRARY_PATH', 'PWD', 'LD_LIBRARY_PATH', 'PYTHONPATH', 'DYNO', 'PYTHONHASHSEED', 'PYTHONUNBUFFERED', 'PYTHONHOME', 'HOME', '_']

I generally go with if 'DYNO' in os.environ:, because it seems to be the most Heroku specific (who else would use the term dyno, right?).

And I also prefer to format it like an if-else statement because it's more explicit:

if 'DYNO' in os.environ:
    debug = False
else:
    debug = True

Answer 2

First set the environment variable ON_HEROKU on heroku:

$ heroku config:set ON_HEROKU=1

Then in settings.py

import os

# define if on heroku environment
ON_HEROKU = 'ON_HEROKU' in os.environ

Answer 3

DATABASE_URL environment variable

in_heroku = False
if 'DATABASE_URL' in os.environ:
    in_heroku = True

I think you need to enable the database for your app with:

heroku addons:create heroku-postgresql:hobby-dev

but it is free and likely what you are going to do anyways.

Heroku makes this environment variable available when running its apps, in particular for usage as:

import dj_database_url
if in_heroku:
    DATABASES = {'default': dj_database_url.config()}
else:
    DATABASES = {
        'default': {
            'ENGINE': 'django.db.backends.sqlite3',
            'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
        }
    }

Not foolproof as that variable might be defined locally, but convenient for simple cases.

heroku run env

might also show other possible variables like:

• DYNO_RAM
• WEB_CONCURRENCY

but I'm not sure if those are documented like DATABASE_URL.

Answer 4

The most reliable way would be to set an environment variable as above. If that's not possible, there are a few signs you can look for in the filesystem, but they may not be / are not foolproof

• Heroku instances all have the path /app - the files and scripts that are running will be under this too, so you can check for the presence of the directory and/or that the scripts are being run from under it.

• There is an empty directory /etc/heroku

• /etc/hosts may have some heroku related domains added ~ $ cat /etc/hosts <snip>.dyno.rt.heroku.com

Any of these can and may change at any moment.

Your milage may vary

Answer 5

An ENV var seems to the most obvious way of doing this. Either look for an ENV var that you know exists, or set your own:

on_heroku = False
if 'YOUR_ENV_VAR' in os.environ:
  on_heroku = True

more at: http://devcenter.heroku.com/articles/config-vars

Answer 6

Read more about it here: https://devcenter.heroku.com/articles/config-vars

My solution:

$ heroku config:set HEROKU=1

These environment variables are persistent – they will remain in place across deploys and app restarts – so unless you need to change values, you only need to set them once.

Then you can test its presence in your app.:

>>> 'HEROKU' in os.environ
True