Persistent & shared directories for Rails apps

Overview

When Cloud 66 deploys your Rails application, we create a number of shared folders that persist between deployments. This guide explains the directory structure of these folders and how they should be used.

$STACK_BASE and $STACK_PATH directories

All Rails applications deployed by Cloud 66 have two special directories on their application server, with the following structure:

• $STACK_BASE
  • /shared
  • /releases
• $STACK_PATH
  • Symlinked to $STACK_BASE/releases/<latest release>

$STACK_BASE stores each recent code deployment in its own directory under a /releases subdirectory. In addition $STACK_BASE has a special subdirectory within /shared named frontend-backend-share that is specifically configured to allow servers with different roles (e.g. workers and web servers) to share files.

$STACK_PATH is a symlink that always points to the most recent release under $STACK_BASE/releases.

How to persist files in your Rails app

If your Rails app requires persistent storage, writing files to $STACK_PATH will not work because as soon as you redeploy we will point the directory at a new folder under /releases.

Instead you should store files under $STACK_BASE/shared- you can create your own subdirectories as needed. Storing files this way will ensure that they are persisted between deployments.

How to share files between frontend and backend

If your Rails app requires that servers with different roles have access to a shared file system, then the best directory to use is $STACK_BASE/shared/frontend-backend-share. This directory is preconfigured to allow secure access from both front and backend Linux users.

Sharing files across multiple servers

If your application runs on multiple web servers, you will not be able to use these folders to persist files reliably because they are not synchronised between servers. For this use case we recommend either a network file-system like GlusterFS, or an object storage service (like Amazon S3 or Google Cloud Storage).