You've just written a masterpiece of a web app. It's fun, it's viral, and it's useful. It's clearly going to be "Sliced Bread 2.0". But what comes next is a series of unforeseen headaches. You'll outgrow your shared hosting and need to get on cloud services. A late night hack session will leave you sleep deprived, and you'll accidentally drop your production database instead of your staging database. Once you serve up a handful of error pages, your praise-singing users will leave you faster than it takes to start a flamewar in #offrails. But wait! Just as Ruby helped you build your killer app, Ruby can also help you manage your infrastructure as your app grows. Read on for a list of useful gems every webapp should have.
When you make a coding mistake, you can revert to a good known commit. But when disaster wrecks havoc with your data, you better have an offsite backup ready to minimize your losses. Enter the backups gem, a DSL for describing your different data stores and offsite storage locations. Once you specify what data stores you use in your application (MySQL, PostgreSQL, Mongo, Redis, and more), and where you want to store it (rsync, S3, CloudFiles), Backup will dump and store your backups. You can specify how many backups you'd like to keep in rotation, and there's various extras like gzip compression, and notifiers for when backups are created or failed to create.
Having backups configured doesn't make you any less absent minded about running your backups. The first remedy that jumps to mind is editing your crontab. But man, it's hard to remember the format on that sucker. If only there was a Ruby wrapper around cron… Fortunately there is! Thanks to the whenever gem, you can define repetitious tasks in a Ruby script.
With the number of cloud services available today, it's becoming more common to have your entire infrastructure hosted in the cloud. Many of these services offer API's to help you tailor and control your environments programmatically. Having API's is great, but it's tough to keep them all in your head.
The fog gem is the one API to rule them all. It provides a consistent interface to several cloud services. There are specific adapters for each cloud service. By following the Fog interface, it makes it really easy to switch between different cloud services. Say you were using Amazon's S3, but wanted to switch to Rackspace's CloudFiles. If you use Fog, it's as simple as replacing your credentials and changing the service name. You can create real cloud servers, or create mock ones for testing. Even if you don't use any cloud services, fog has adapters for non-cloud servers and filesystems.
Hoptoad is a household name in the Ruby community. It catches exceptions created by your app, and sends them into a pretty web interface and other notifications. If you can't use Hoptoad because of a firewall, check out the self-hostable Errbit.
When your infrastructure isn't running smoothly, it better be raising all kinds of alarms and sirens to get someone to fix it. Two popular monitoring solutions are God, and Monit. God lets you configure which services you want to monitor in Ruby, and the Monit gem gives you an interface to query services you have registered with Monit. If you have a Ruby script that you'd like to have running like a traditional Unix daemon, check out the daemons gem. It wraps around your existing Ruby script and gives you a 'start', 'stop', 'restart' command line interface that makes it easier to monitor. Don't forget to monitor your background services, it sucks to have all your users find your broken server before you do.
Your application is happily running in production, but all of a sudden, it decides to implode on itself for a specific user when they update their avatar. Try as you might, you just can't reproduce the bug locally. You could do some cowboy debugging on production, but you'll end up dropping your entire database on accident. Oops.
It's times like these that you'll be thankful you have a staging environment setup. If you use capistrano, make sure to check out how to use capistrano-ext gem, and its multi-stage deploy functionality. To reproduce your bug on the same data, you can use the taps gem to transfer your data from your production database to your staging database. If you're using Heroku then it's already built-in.
Before you start testing your mailers on staging, do all of your users a favor and install the mail_safe gem. It stubs out ActionMailer so that your users don't get your testing spam. It also lets you send emails to your own email address for testing.
Thor is a good foundation for writing CLI utilities in Ruby. It has interfaces for manipulating files and directories, parsing command line options, and manipulating processes.
Capistrano helps you deploy your application, and Chef configures and deploys your servers and services. If you use Vagrant for managing development virtual machines, you can reuse your Chef cookbooks for production.
All of these gems help us maintain our application infrastructure in a robust way. It frees us from running one-off scripts and hacks in production and gives us a repeatable process for managing everything our app runs on. And on top of all the awesome functionality these tools provide, we can also write Ruby to interact with them and version control them alongside our code. So for your next killer webapp, don't forget to add some killer devops to go along with it.