Running WordPress on Heroku + Amazon RDS

With the announcement of the Heroku and Facebook partnership yesterday, Heroku quietly confirmed support for two new languages, Python and PHP. The self-proclaimed polyglot platform, Heroku's Celadon Cedar Stack now has a considerable advantage over newcomers like PHP Fog, and by avoiding mostly separate, language-specific products.

To test out Heroku's PHP support (version 5.3.6), I deployed WordPress. One of the current limitations is the lack of native MySQL support, outside of hooking into the Xeround Cloud DB or Amazon RDS. I've found one blog post that suggested using the default PostgreSQL backend that Heroku provides with the 'PG4WP' WordPress plugin, enabling WordPress to be used with a PostgreSQL database. While this may work, it lacks most plugin support and is more of a bandaid for the platform limitations. Instead, you can use Amazon's Relational Database Service (RDS) addon.

Amazon RDS is a service that allows you to set up, operate and scale a dedicated MySQL database server on top of EC2. In addition to standard MySQL features, RDS offers the following functionality:

  • Automated backups
  • Point-in-time recovery
  • Seamless vertical scaling between instance types

The free Amazon RDS add-on lets you connect your Heroku app to an RDS instance and seamlessly use it in place of the standard, Heroku-provided PostgreSQL database. To get started, you should configure the RDS command line toolkit and Heroku gem if you haven't already. Let's start by creating the RDS database instance on your local machine:

rds-create-db-instance --db-instance-identifier [name]\
  --allocated-storage 5 \
  --db-instance-class db.m1.small  \
  --engine MySQL5.1 \
  --master-username [user] \
  --master-user-password [pw] \
  --db-name [name] \

This will take a few minutes. Once the database is provisioned, add your local IP address to the security group -- assuming your workstation’s public IP is

rds-authorize-db-security-group-ingress default --cidr-ip

Heroku also needs to be able to access your RDS instance. To allow Heroku’s cloud through the RDS firewall, run the following command:

rds-authorize-db-security-group-ingress default \
    --ec2-security-group-name default \
    --ec2-security-group-owner-id 098166147350

Note: Previously, Heroku recommended using their AWS security group and AWS account ID to grant apps access to other services running on AWS. This approach is no longer recommended and the relevant documentation has been removed. Reasons for no longer recommending this include:

  • Cross-security grants do not work with AWS VPC (which is now the default on AWS)
  • It is not safe because it grants access to all apps running on Heroku, not just yours
  • Does not work across AWS regions
  • Heroku may in the future run apps in a VPC or in a different region or use a different AWS account

If you are using Heroku with a AWS RDS database, I would strongly recommend using SSL to secure database connections. Find links and details in the Amazon RDS Dev Center article.

Now we can begin building the application layer. Since we're going to be using Git for version control, I'd suggest cloning WordPress from the GitHub repository; it is synced from Automattic's SVN repository every 15 minutes, including branches and tags:

git clone git://
cd WordPress

Before we start making any changes to file structure, we should make our own Git repository and start committing. Note here that you'll want to populate the wp-config.php with the MySQL credentials from the rds-create-db-instance command above:

git init
mv wp-config-sample.php wp-config.php
git add .
git commit -m 'initial commit'

Now, create the stack and enable the RDS addon with your MySQL credentials. Once the stack has been created, you can deploy:

heroku create --stack cedar
heroku addons:add amazon_rds url=mysql://
git push heroku master

The output should look something like this:

➜ wp-heroku-test git:(master) git push heroku master
Counting objects: 985, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (965/965), done.
Writing objects: 100% (985/985), 3.65 MiB | 221 KiB/s, done.
Total 985 (delta 66), reused 0 (delta 0)

-----> Heroku receiving push
-----> PHP app detected
-----> Bundling Apache v2.2.19
-----> Bundling PHP v5.3.6
-----> Discovering process types
       Procfile declares types -> (none)
       Default types for PHP   -> web
-----> Compiled slug size is 24.9MB
-----> Launching... done, v4 deployed to Heroku

 * [new branch]      master -> master


  • A commenter on HackerNews noted that the slug is still read-only, but the ephemeral filesystem is writable. The slug is what gets deployed on each new dyno spawned. The ephemeral filesystem is the individual file system on each dyno. So a plugin like WP Super Cache would be able to write to the file system, but that cache would only exist for the individual dyno that wrote it.

  • Because of the usage concerns of media and content uploads, I'd suggest using a CDN or Amazon S3 for storing images and attachments.

  • The zlib extension for PHP is not compiled on the Celadon Cedar Stack. Theme and plugin uploads through the WordPress admin panel will fail. To get around this, set up your themes and plugins on your local workstation first, commit and deploy.

  • Do not include a phpinfo page in the document root as it will contain your database credentials in plain text.

  • If you want to have pretty permalinks, create the .htaccess file on your local machine and populate the mod_rewrite rules prior to deploying.