zuul/doc/source/admin/components.rst

title

Components

Components

Zuul is a distributed system consisting of several components, each of which is described below. All Zuul processes read the /etc/zuul/zuul.conf file (an alternate location may be supplied on the command line) which uses an INI file syntax. Each component may have its own configuration file, though you may find it simpler to use the same file for all components.

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.

Common

The following applies to all Zuul components.

Configuration

The following sections of zuul.conf are used by all Zuul components:

gearman

Client connection information for gearman.

server

Hostname or IP address of the Gearman server. server=gearman.example.com (required)

port

Port on which the Gearman server is listening. port=4730 (optional)

ssl_ca

Optional: An openssl file containing a set of concatenated “certification authority” certificates in PEM formet.

ssl_cert

Optional: An openssl file containing the client public certificate in PEM format.

ssl_key

Optional: An openssl file containing the client private key in PEM format.

zookeeper

hosts

A list of zookeeper hosts for Zuul to use when communicating with Nodepool. hosts=zk1.example.com,zk2.example.com,zk3.example.com

Scheduler

The scheduler is the primary component of Zuul. The scheduler is not a scalable component; one, and only one, scheduler must be running at all times for Zuul to be operational. It receives events from any connections to remote systems which have been configured, enqueues items into pipelines, distributes jobs to executors, and reports results.

Configuration

The following sections of zuul.conf are used by the scheduler:

gearman_server

The builtin gearman server. Zuul can fork a gearman process from itself rather than connecting to an external one.

start

Whether to start the internal Gearman server (default: False). start=true

listen_address

IP address or domain name on which to listen (default: all addresses). listen_address=127.0.0.1

log_config

Path to log config file for internal Gearman server. log_config=/etc/zuul/gearman-logging.yaml

ssl_ca

Optional: An openssl file containing a set of concatenated “certification authority” certificates in PEM formet.

ssl_cert

Optional: An openssl file containing the server public certificate in PEM format.

ssl_key

Optional: An openssl file containing the server private key in PEM format.

webapp

listen_address

IP address or domain name on which to listen (default: 0.0.0.0). listen_address=127.0.0.1

port

Port on which the webapp is listening (default: 8001). port=8008

status_expiry

Zuul will cache the status.json file for this many seconds. This is an optional value and 1 is used by default. status_expiry=1

status_url

URL that will be posted in Zuul comments made to changes when starting jobs for a change. Used by zuul-scheduler only. status_url=https://zuul.example.com/status

scheduler

tenant_config

Path to tenant config file. layout_config=/etc/zuul/tenant.yaml

log_config

Path to log config file. log_config=/etc/zuul/scheduler-logging.yaml

pidfile

Path to PID lock file. pidfile=/var/run/zuul/scheduler.pid

state_dir

Path to directory that Zuul should save state to. state_dir=/var/lib/zuul

Operation

To start the scheduler, run zuul-scheduler. To stop it, kill the PID which was saved in the pidfile specified in the configuration.

Most of Zuul's configuration is automatically updated as changes to the repositories which contain it are merged. However, Zuul must be explicitly notified of changes to the tenant config file, since it is not read from a git repository. To do so, send the scheduler PID (saved in the pidfile specified in the configuration) a SIGHUP signal.

Merger

Mergers are an optional Zuul service; they are not required for Zuul to operate, but some high volume sites may benefit from running them. Zuul performs quite a lot of git operations in the course of its work. Each change that is to be tested must be speculatively merged with the current state of its target branch to ensure that it can merge, and to ensure that the tests that Zuul perform accurately represent the outcome of merging the change. Because Zuul's configuration is stored in the git repos it interacts with, and is dynamically evaluated, Zuul often needs to perform a speculative merge in order to determine whether it needs to perform any further actions.

All of these git operations add up, and while Zuul executors can also perform them, large numbers may impact their ability to run jobs. Therefore, administrators may wish to run standalone mergers in order to reduce the load on executors.

Configuration

The following section of zuul.conf is used by the merger:

merger

git_dir

Directory that Zuul should clone local git repositories to. git_dir=/var/lib/zuul/git

git_user_email

Optional: Value to pass to git config user.email. git_user_email=zuul@example.com

git_user_name

Optional: Value to pass to git config user.name. git_user_name=zuul

log_config

Path to log config file for the merger process. log_config=/etc/zuul/logging.yaml

pidfile

Path to PID lock file for the merger process. pidfile=/var/run/zuul-merger/merger.pid

Operation

To start the merger, run zuul-merger. To stop it, kill the PID which was saved in the pidfile specified in the configuration.

Executor

Executors are responsible for running jobs. At the start of each job, an executor prepares an environment in which to run Ansible which contains all of the git repositories specified by the job with all dependent changes merged into their appropriate branches. The branch corresponding to the proposed change will be checked out (in all projects, if it exists). Any roles specified by the job will also be present (also with dependent changes merged, if appropriate) and added to the Ansible role path. The executor also prepares an Ansible inventory file with all of the nodes requested by the job.

The executor also contains a merger. This is used by the executor to prepare the git repositories used by jobs, but is also available to perform any tasks normally performed by standalone mergers. Because the executor performs both roles, small Zuul installations may not need to run standalone mergers.

Trusted and Untrusted Playbooks

The executor runs playbooks in one of two execution contexts depending on whether the project containing the playbook is a config project or an untrusted project. If the playbook is in a config project, the executor runs the playbook in the trusted execution context, otherwise, it is run in the untrusted execution context.

Both execution contexts use bubblewrap to create a namespace to ensure that playbook executions are isolated and are unable to access files outside of a restricted environment. The administrator may configure additional local directories on the executor to be made available to the restricted environment.

The trusted execution context has access to all Ansible features, including the ability to load custom Ansible modules. Needless to say, extra scrutiny should be given to code that runs in a trusted context as it could be used to compromise other jobs running on the executor, or the executor itself, especially if the administrator has granted additional access through bubblewrap, or a method of escaping the restricted environment created by bubblewrap is found.

Playbooks run in the untrusted execution context are not permitted to load additional Ansible modules or access files outside of the restricted environment prepared for them by the executor. In addition to the bubblewrap environment applied to both execution contexts, in the untrusted context some standard Ansible modules are replaced with versions which prohibit some actions, including attempts to access files outside of the restricted execution context. These redundant protections are made as part of a defense-in-depth strategy.

Configuration

The following sections of zuul.conf are used by the executor:

executor

finger_port

Port to use for finger log streamer. finger_port=79

git_dir

Directory that Zuul should clone local git repositories to. git_dir=/var/lib/zuul/git

log_config

Path to log config file for the executor process. log_config=/etc/zuul/logging.yaml

private_key_file

SSH private key file to be used when logging into worker nodes. private_key_file=~/.ssh/id_rsa

user

User ID for the zuul-executor process. In normal operation as a daemon, the executor should be started as the root user, but it will drop privileges to this user during startup. user=zuul

merger

git_user_email

Optional: Value to pass to git config user.email. git_user_email=zuul@example.com

git_user_name

Optional: Value to pass to git config user.name. git_user_name=zuul

Operation

To start the executor, run zuul-executor.

There are several commands which can be run to control the executor's behavior once it is running.

To stop the executor immediately, aborting all jobs (they may be relaunched according to their retry policy), run zuul-executor stop.

To request that the executor stop executing new jobs and exit when all currently running jobs have completed, run zuul-executor graceful.

To enable or disable running Ansible in verbose mode (with the '-vvv' argument to ansible-playbook) run zuul-executor verbose and zuul-executor unverbose.