Rails with Heroku: How to download a CSV created by a rake task

Question

I deployed "Harrys Prelauncher" on Heroku and try to do the teardown (currently just testing). See here: https://github.com/harrystech/prelaunchr#teardown

After running the rake task ...

heroku run rake prelaunchr:create_winner_csvs

... a csv file is created in "/lib/assets", but I dont know how to access the file (it works locally in development).

How can I download or access the file?

Answer 1

Heroku uses "ephemeral" filesystem that is not guaranteed to preserve changes made at runtime . Simply put, if it's not pushed to git (I assume you're using git with heroku), it's not guaranteed to exist in all the instances of your app. It may exist in one of them, but you may have no simple way of accessing that specific filesystem. And you shouldn't, really.

It's done like that so that multiple instances of the same app can be fired up seamlessly. Of course, that requires some discipline: storage of any meaningful state outside: in the database, on external disk, anywhere. The benefit of this is horizontal scalability: should you be short on resources, you can fire up another web dyno that would (normally) behave exactly the same way. New dynos are started from bundles that are packed on git push and thus do not contain any changes you may have made in another instance.

A workaround may be running heroku run bash , so that you end up in an interactive shell linked to another instance of your bundle.

Then you can make that file (by running your rake task) and access its contents in any way you deem reasonable. Text files can be echoed into the console with cat and copy-pasted anywhere else. That's a dirty way.

A much cleaner way would be rigging the app to send the file in question via email. and it's one of the few reasonable ways if that rake task is invoked by the Rails app itself.

Answer 2

I ran into this problem recently while developing the Prelaunchr campaign for a client. Assuming you have a local version of your app, you can "pull" your Heroku database down to your local machine, set that as your development database in database.yml, and run the rake task from your local app, which should now have the same database as your heroku version. Here is the command to pull the db (subbing out name_for_database & heroku_app_name with your own):

heroku pg:pull HEROKU_POSTGRESQL_COPPER_URL name_for_database --app heroku_app_name

Make sure to restart your local server to see the new database info populated.