Using the Zulip Docker Compose repository

Understanding Docker

Docker and other container systems are built around shareable container images. An image is a read-only template with instructions for creating a container.

Often, an image is based on another image, with a bit of additional customization. For example, Zulip’s zulip-postgresql image extends the standard postgresql image (by installing a couple postgres extensions). Meanwhile, the zulip image is built on top of a standard ubuntu image, adding all the code for a Zulip application/web server.

Every time you boot a container based on a given image, it’s like booting off a CD-ROM: you get the exact same image (and anything written to the image’s filesystem is lost). To handle persistent state that needs to persist after the Docker equivalent of a reboot or upgrades (like uploaded files or the Zulip database), container systems let you configure certain directories inside the container from the host.

Volumes

This project’s docker-compose.yml configuration file uses Docker managed volumes to store persistent Zulip data. If you use the Docker Compose deployment, you should make sure that Zulip’s volumes are backed up, to ensure that Zulip’s data is backed up.

Configuration

While it is possible to configure the project using files on disk, as in a standard Zulip deployment, most Docker deployments use environment variables to tell the container how to configure itself. All of the standard Zulip settings and system configuration options are available via environment variables.

Secrets

Zulip’s Docker container uses Docker secrets to synchronize secrets between services, as well as within Zulip itself. Secrets are not stored in the Docker Compose configuration, but are instead stored in one or more adjacent files. This keeps the configuration separate from sensitive information, and makes them easier to provide to both sides of a secured connection.

Dependencies

This project defines a Docker image for a Zulip server, as well as sample configuration to run that Zulip server with each of the major services that Zulip uses in its own container: redis, postgres, rabbitmq, memcached.