As I understand Herokus Ephemeral filesystem will only allow you write access to a temporary folder. Created files in that folder will be discarded when the dyno the files was created with is stopped or restarted.
What I don't understand is what happens if the dyno is not stopped or restarted? Will files still be discarded after a certain time?
We are currently building a system that generates pdf files and forwards them via mail (or you can download the file). Do I need to remove the pdf files myself after they have been sent/downloaded, or can I rely on them being removed automatically by Heroku?
Dynos are cycled every 24 hours so your files will never last longer than that.
Therefore, it's safe to say that you don't need to worry about archiving these files off.
Note; just a small thing. Cedar lets you write to anywhere on the dyno. Bamboo only lets you write to /tmp.
来源：https://stackoverflow.com/questions/14935497/heroku-ephemeral-filesystem-and-temporary-files