Synching Your Amazon S3 Asset Host using Capistrano

Synching Your Amazon S3 Asset Host using Capistrano

So you’ve got multiple asset hosts running in your Rails application, and you’re using Amazon’s S3 to host your assets. Now you want to make sure that your assets are kept up to date. This plugin is a Capistrano recipe that keeps the asset hosts synchronized with the public directory in your subversion repository.


After you get everything setup and do your first deploy, just run cap deploy as normal and all changed files in RAILS_ROOT/public will be uploaded to all of your asset host buckets before the final deploy:symlink task.

  • cap s3_asset_host:synch_public (This is the default task)
  • cap s3_asset_host:reset_and_synch
  • cap s3_asset_host:setup
  • cap s3_asset_host:create_buckets
  • cap s3_asset_host:delete_all
  • cap s3_asset_host:connect

You can get documentation on these tasks by running cap -T


This plug-in is a Capistrano extension. It requires Capistrano 2.0.0 or greater.

You will also require the aws-s3 gem

If you want to use more than one asset host, then you have to either install the multiple asset hosts plugin
or upgrade to Rails 2.0 (see setting up multiple asset hosts in Rails)


To set-up, you need to do the following

  • Install the plugin
  • Install the AWS-S3 gem.
  • Set up your Rails application to use asset hosts.
  • Set up your asset hosts.
  • Configure Capistrano.

Installing the plug-in

From RAILS_ROOT, run:

script/plugin install git://

Installing the AWS-S3 gem

You need to do this on both your local computer and the computer that is defined as the asset_host_syncher (see Capistrano Configuration, below).

$> sudo gem install aws-s3

Setting up your Rails app to use asset hosts

Single asset host

For a single asset host, simply add the following line to RAILS_ROOT/config/environments/production.rb:

config.action_controller.asset_host = ""

Multiple asset hosts

Follow the instructions in “setting up multiple asset hosts in Rails”::/2007/10/setting-up-multiple-asset-hosts-in-rails.html

Setting up your asset hosts

Set up a CNAME entry for each asset host pointing to How you do this depends on your domain host. Here’s what it looks like on easydns

You may need to wait up to 24 hours for the DNS entries for these new hosts to propagate.

Configuring Capistrano

Capistrano installation

This plugin requires Capistrano 2.0.0 or greater.

To upgrade to the latest version (currently 2.1.0):

$> gem install capistrano

Once the plug-in is installed, make sure that the recipes are seen by Capistrano

$> cap -T | grep s3_asset_host

should return a bunch of tasks. If you don’t see anything listed, then you need to update your Capfile by doing the following (this is from Jamis Buck):

In Capistrano 2.1.0 or above:

$> rm Capfile
$> capify .

If you do not want to delete your Capify file, or if you are using Capistrano 2.0.0, add the following line to your Capify file:
Dir['vendor/plugins/*/recipes/*.rb'].each { |plugin| load(plugin) }

Capistrano configuration

In RAILS_ROOT/config/deploy.rb
Specify one of your web hosts as an “asset_host_syncher”. If you only have one web host, you don’t make a new line for this,
just edit the existing line that sets your :web role

role :web, webserver1, :asset_host_syncher => true

tell Capistrano to synch your s3 hosts before doing the final symlink task:

before "deploy:symlink", "s3_asset_host:synch_public"
S3 configuration

Create a file in RAILS_ROOT/config called synch_s3_asset_host.yml. Add the following to it,
and edit to suit:

AWS_ACCESS_KEY_ID: ‘your access key here’
AWS_SECRET_ACCESS_KEY: ‘your secret key here’
asset_host_name: “”

  1. dry_run: false # Set to true if you want to test the asset_host uploading without doing anything on Amazon S3

The first deploy

Commit all changes to your rails application and do the initial bucket setup:

$> svn add config/synch_s3_asset_host.yml
$> svn add vendor/plugins/synch_s3_asset_host
$> svn commit -m "Adding synch_s3_asset_host plugin"
$> cap s3_asset_host:setup
$> cap deploy

This will do the following:

  • Create your Amazon S3 AWS buckets
  • upload everything in RAILS_ROOT/public (in your svn repository) to each bucket
  • Set the revision in each bucket to the latest revision in your repository.

This could take a while if you have lots of images or other big files.

You’re done!

That should do it. Now, every time you run cap deploy, your asset hosts should be updated with any changes to files in RAILS_ROOT/public.

Let me know if you have any problems, suggestions or comments.

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