Jessie Frazelle, member of Docker's core team, is responsible for Docker's testing infrastructure. Frazelle described how that infrastructure is itself built on Docker containers.
The testing infrastructure consists of around 50 servers. They account for the six different storage drivers, which determine how Docker stores containers, all the Linux distros and the various Linux kernel versions that Docker supports. The Windows Docker Client, which provides a lightweight VM to run Docker hosts on Windows, is also accounted for.
Pushes to master and pull requests (PR) have their own workflows. Besides executing all the Docker tests, every successful push to master publishes the Docker binaries and docs for those who want to try the bleeding edge. The Docker Binary Builder (docker-bb) handles building the master binaries.
Pull requests have their own workflow and servers. Each pull request - there are more than 100 per week - is exercised against the Docker tests, the new experimental binary and the Windows Docker client. Leeroy, a small app built by Frazelle, manages all the PR builds. Its responsibilities include updating the status (pending, success, failure or error) of the PR and validating the Docker Developer Certificate of Origin.
Docker's continuous integration server is Jenkins, as it provides the flexibility and control the team needs. As expected, Frazelle uses the official image to run Jenkins inside a container.
Consul, a service discovery tool, is a key part of the testing infrastructure. Frazelle uses its services tagging capability to track data such as Linux kernel versions or storage drivers. This, in turn, helps troubleshooting activities. Consul's health checking is also leveraged with the help of consul-alerts to notify the team when a service goes down.
The Docker team uses nsq, a real-time distributed messaging platform, to integrate many of these processes. For instance to link GitHub hooks to docker-bb or to deploy the master docs.
All the services that enable the testing infrastructure run inside Docker containers. The testing infrastructure uses the latest Docker Release Candidate whenever there is one. Sometimes it uses the latest master binaries to catch bugs as early as possible.