Creating temporary files in Heroku

Question

I have an app hosted @ Heroku. The app depends on some feeds which are fetched using a socket listener. The socket listener gets one line of XML per second. Once I detect the end of file signal from the listener, I upload the file to Amazon S3 servers. But, until the end of file signal is received, is it possible to save the file content as a temporary file in Heroku?

Answer 1

You may be able to use the #{RAILS_ROOT}/tmp/ directory or Rails.root.join('tmp').to_s:

Aspen & Bamboo
[...]
There are two directories that are writeable: ./tmp and ./log (under your application root).
[...]

Cedar
Cedar offers an ephemeral writeable filesystem. You can write out to disk anywhere you would like. Your changes will be lost on dyno restart and spin-up.

RAILS_ROOT is for older Rails versions, Rails.root is for newer versions.

You can't depend on anything surviving across requests of course, there's no guarantee that you'll even be working with the same dyno.

As long as you stay within the same process or request, Rails.root.join('tmp') should be usable. If you need the temporary data to survive across requests or processes then you're better off using something else (such as MongoDB or PostgreSQL) as a collecting ground for your data on its way to S3.

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Thanks to Benjamin Wheeler for the heads up about the RAILS_ROOT to Rails.root change.