Using Wildcard Domains with Rails

Sep 13, 2011  -  Comments

Working on a recent project, I needed to allow users to set custom domains to point to their account pages on my server. They would set their domain when they registered, then set an A Record with their DNS to point to my server. The only problem was, I didn't know how to get Rails to do this.

The domain is already saved in the database, but I needed to tell the router to look for any incoming requests to a domain that doesn't match my primary domain (in this example, we'll say my primary domain is example.com). Thanks to Rails 3, I could just add a routing constraint (which can take a class as argument), like so

  MyApp::Application.routes.draw do
    # domain routes (THIS IS THE IMPORTANT PART)
    constraints(Domain) do
      match '/index.html' => 'user#show', :as => :user_domain
      resources :tasks
      resources :projects
      # any other routes that are domain-specific
    # this needs to be below the "domain" section
    root :to => 'site#index'

Notice that the root path is below the domain routes. This is important because it will get triggered before the domain routes otherwise (because routes are first come, first served). With these routes in place, it's as easy as finding the user by domain when we get a request.

We added the Domain class as a constraints argument, now we need to add that file. You can add the following domain.rb to your lib folder and make sure it's getting loaded on application boot.

  class Domain
    def self.matches?(request)
      request.domain.present? && request.domain != 'example.com'

It's as easy as that. We just check to make sure the domain is present and that it doesn't match our primary domain. This constraint will match any domain other than our primary domain.

As for server configuration, you have to tell your server to accept all incoming requests, regardless of domain. Below is a sample Apache virtualhost to accomplish this. Notice that we don't specify a ServerName or ServerAlias, we want it to match everything.

  <VirtualHost *:80>
    DocumentRoot /path/to/my_app/public

    <Directory /path/to/my_app/public>
      Options FollowSymLinks
      AllowOverride None
      Order allow,deny
      Allow from all

IMPORTANT: You need to ensure that this virtualhost entry is loaded last. If you have any other virtualhosts that specify a ServerName, then they need to be loaded before this one. We're using this entry as a catch-all to route to our rails app. If you have all of your virtualhosts in one file, just put this entry last. If each entry is in its own file, just make sure this file is loaded last (you might add a zzz_ to the start of the filename to make sure).

Tagged: routesrails3

Using God Gem to Monitor mySQL

Oct 02, 2011  -  Comments

I recently ran into a problem on a client server where the msyqld process died, and neither of us noticed it for almost 24 hours. That meant that the site was completely useless that entire time. Needless to say, the client wasn't thrilled about this.

I told him that I'd look into setting up a monitoring service to, at the very least, notify me if msyqld ever crashed. During my research, I stumbled upon the god gem (which I'd used in the past to monitor mongrel processes back in the days before Passenger). I didn't realize it could be used to monitor other processes as well, such as msyqld.

God is a rubygem, so it's easy to install on any *nix operating system. It's config files are also written in Ruby, so that makes it even better.

What you'll need to get the script running:

  1. Install the god gem (as root).
    sudo gem install god
  2. Find the location of your msyqld pid file.
    mysqladmin -u root -p variables | grep pid_file
  3. Determine the command to start/stop/restart the msyqld service. Usually /etc/init.d/mysqld

Here is the config file I wrote to watch my mysqld process:

  # run in non-daemonized mode (so you can monitor it) with `god -c /path/to/mysql.god -D`
  # run normally with `god -c /path/to/mysql.god`

  # Settings for email notifications (optional)
  God::Contacts::Email.defaults do |d|
    d.from_email = 'god@my-app.com'
    d.from_name = 'God'
    d.delivery_method = :smtp # this can also be :sendmail
    d.server_host = 'smtp.myapp.com'
    d.server_port = 25
    d.server_auth = true
    d.server_domain = 'myapp.com'
    d.server_user = 'smtp_user@myapp.com'
    d.server_password = 'password'

  # you can create as many email entries as you'd like
  God.contact(:email) do |c|
    c.name = 'me'
    c.to_email = 'me@email.com'

  God.watch do |w|
    # you can name this whatever you want
    w.name = "mySQL Server"

    # polling interval
    w.interval = 30.seconds

    # command to start service
    w.start = "/etc/initd/mysqld_start_ampamp_/etc/initd/httpd_restart/index.html"

    # command to stop service
    w.stop = "/etc/initd/mysqld_stop/index.html"

    # command to restart service
    w.restart = "/etc/initd/mysqld_restart_ampamp_/etc/initd/httpd_restart/index.html"

    # how long to wait after starting service before monitoring resumes
    w.start_grace = 20.seconds

    # how long to wait after restarting service before monitoring resumes
    w.restart_grace = 20.seconds

    # location of pid file
    w.pid_file = "/var/run/mysqld/mysqld.pid"

    # tell god to delete the pid file when mysqld crashes

    # determine the state on startup
    w.transition(:init, { true => :up, false => :start }) do |on|
      on.condition(:process_running) do |c|
        c.running = true

    # determine when process has finished starting
    w.transition([:start, :restart], :up) do |on|
      on.condition(:process_running) do |c|
        c.running = true
      # failsafe
      on.condition(:tries) do |c|
        c.times = 8
        c.within = 2.minutes
        c.transition = :start

    # start if process is not running
    w.transition(:up, :start) do |on|
      on.condition(:process_exits) do |c|
        # send an email to me to notify me that the service has crashed
        c.notify = 'me'

    # lifecycle
    w.lifecycle do |on|
      # If the service keeps triggering a restart over and over, it is considered to be "flapping".
      on.condition(:flapping) do |c|
        c.to_state = [:start, :restart]
        c.times = 5
        c.within = 1.minute
        c.transition = :unmonitored
        # If the service is flapping, wait 10 minutes, then try to start/restart again.
        c.retry_in = 10.minutes
        c.retry_times = 5
        c.retry_within = 2.hours

A few things to note about my script:

  1. In my start and restart commands, I also restart Apache. Running my site with Passenger, I would get a Rack error when mysqld restarted, but apache hadn't. YMMV.
  2. I'm using an SMTP server for my email notification. You can also use sendmail, or you can exclude the email notifications altogether.
  3. When running the script for the first time, it's a good idea to add the -D flag. This runs god in non-daemonized mode so all output is piped to STDOUT. That way, you can watch what it's doing to ensure everything is working correctly.

For more information about the god gem, see their site: god.rubyforge.org

Tagged: rubymysqlgod