Component Overview

Zuul is a distributed system consisting of several components, each of which is described below.

Each of the Zuul processes may run on the same host, or different hosts. Within Zuul, the components communicate with the scheduler via the Gearman protocol, so each Zuul component needs to be able to connect to the host running the Gearman server (the scheduler has a built-in Gearman server which is recommended) on the Gearman port – TCP port 4730 by default.

The Zuul scheduler communicates with Nodepool via the ZooKeeper protocol. Nodepool requires an external ZooKeeper cluster, and the Zuul scheduler needs to be able to connect to the hosts in that cluster on TCP port 2181 or 2281.

Both the Nodepool launchers and Zuul executors need to be able to communicate with the hosts which nodepool provides. If these are on private networks, the Executors will need to be able to route traffic to them.

Only Zuul fingergw and Zuul web need to be publicly accessible; executors never do. Executors should be accessible on TCP port 7900 by fingergw and web.

A database is required and configured in database section of /etc/zuul/zuul.conf. Both Zuul scheduler and Zuul web will need access to it.

If statsd is enabled, the executors and scheduler needs to be able to emit data to statsd. Statsd can be configured to run on each host and forward data, or services may emit to a centralized statsd collector. Statsd listens on UDP port 8125 by default.

A minimal Zuul system may consist of a Scheduler and Executor both running on the same host. Larger installations should consider running multiple executors, each on a dedicated host, and running mergers on dedicated hosts as well.