The Story of Apollo - Amazon's Deployment Engine - All Things Distributed
Automated deployments are the backbone of a strong DevOps environment. Without efficient, reliable, and repeatable software updates, engineers need to redirect their focus from developing new features to managing and debugging their deployments. Amazon first faced this challenge many years ago.
When making the move to a service-oriented architecture, Amazon refactored its software into small independent services and restructured its organization into small autonomous teams. Each team took on full ownership of the development and operation of a single service, and they worked directly with their customers to improve it. With this clear focus and control, the teams were able to quickly produce new features, but their deployment process soon became a bottleneck. Manual deployment steps slowed down releases and introduced bugs caused by human error. Many teams started to fully automate their deployments to fix this, but that was not as simple as it first appeared.
Deploying software to a single host is easy. You can SSH into a machine, run a script, get the result, and you're done. The Amazon production environment, however, is more complex than that. Amazon web applications and web services run across large fleets of hosts spanning multiple data centers. The applications cannot afford any downtime, planned or otherwise. An automated deployment system needs to carefully sequence a software update across a fleet while it is actively receiving traffic. The system also requires the built-in logic to correctly respond to the many potential failure cases.
It didn't make sense for each of the small service teams to duplicate this work, so Amazon created a shared internal deployment service called Apollo. Apollo's job was to reliably deploy a specified set of software across a target fleet of hosts. Developers could define their software setup process for a single host, and Apollo would coordinate that update across an entire fleet of hosts. This made it easy for developers to "push-button" deploy their application to a development host for debugging, to a staging environment for tests, and finally to production to release an update to customers. The added efficiency and reliability of automated deployments removed the bottleneck and enabled the teams to rapidly deliver new features for their services.
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