:title: Components .. _components: Components ========== Zuul is a distributed system consisting of several components, each of which is described below. .. graphviz:: :align: center graph { node [shape=box] Gearman [shape=ellipse] Gerrit [fontcolor=grey] Zookeeper [shape=ellipse] Nodepool GitHub [fontcolor=grey] Merger -- Gearman Executor -- Gearman Web -- Gearman Gearman -- Scheduler; Scheduler -- Gerrit; Scheduler -- Zookeeper; Zookeeper -- Nodepool; Scheduler -- GitHub; } 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. An example ``zuul.conf``: .. code-block:: ini [gearman] server=localhost [gearman_server] start=true log_config=/etc/zuul/gearman-logging.yaml [zookeeper] hosts=zk1.example.com,zk2.example.com,zk3.example.com [webapp] status_url=https://zuul.example.com/status [scheduler] log_config=/etc/zuul/scheduler-logging.yaml A minimal Zuul system may consist of a :ref:`scheduler` and :ref:`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: .. attr:: gearman Client connection information for Gearman. .. attr:: server :required: Hostname or IP address of the Gearman server. .. attr:: port :default: 4730 Port on which the Gearman server is listening. .. attr:: ssl_ca An openssl file containing a set of concatenated “certification authority” certificates in PEM formet. .. attr:: ssl_cert An openssl file containing the client public certificate in PEM format. .. attr:: ssl_key An openssl file containing the client private key in PEM format. .. NOTE: this is a white lie at this point, since only the scheduler uses this, however, we expect other components to use it later, so it's reasonable for admins to plan for this now. .. attr:: zookeeper Client connection information for ZooKeeper .. attr:: hosts :required: A list of zookeeper hosts for Zuul to use when communicating with Nodepool. .. _scheduler: 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: .. attr:: gearman_server The builtin gearman server. Zuul can fork a gearman process from itself rather than connecting to an external one. .. attr:: start :default: false Whether to start the internal Gearman server. .. attr:: listen_address :default: all addresses IP address or domain name on which to listen. .. attr:: log_config Path to log config file for internal Gearman server. .. attr:: ssl_ca An openssl file containing a set of concatenated “certification authority” certificates in PEM formet. .. attr:: ssl_cert An openssl file containing the server public certificate in PEM format. .. attr:: ssl_key An openssl file containing the server private key in PEM format. .. attr:: webapp .. attr:: listen_address :default: all addresses IP address or domain name on which to listen. .. attr:: port :default: 8001 Port on which the webapp is listening. .. attr:: status_expiry :default: 1 Zuul will cache the status.json file for this many seconds. .. attr:: status_url URL that will be posted in Zuul comments made to changes when starting jobs for a change. .. TODO: is this effectively required? .. attr:: scheduler .. attr:: tenant_config :required: Path to :ref:`tenant-config` file. .. attr:: log_config Path to log config file. .. attr:: pidfile :default: /var/run/zuul-schedurecr/zuul-scheduler.pid Path to PID lock file. .. attr:: state_dir :default: /var/lib/zuul Path to directory in which Zuul should save its state. 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: .. attr:: merger .. attr:: git_dir Directory in which Zuul should clone git repositories. .. attr:: git_user_email Value to pass to `git config user.email `_. .. attr:: git_user_name Value to pass to `git config user.name `_. .. attr:: log_config Path to log config file for the merger process. .. attr:: pidfile :default: /var/run/zuul-merger/zuul-merger.pid Path to PID lock file for the merger process. 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: 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 :term:`config-project` or an :term:`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. .. _bubblewrap: https://github.com/projectatomic/bubblewrap Configuration ~~~~~~~~~~~~~ The following sections of ``zuul.conf`` are used by the executor: .. attr:: executor .. attr:: finger_port :default: 79 Port to use for finger log streamer. .. attr:: git_dir :default: /var/lib/zuul/git Directory that Zuul should clone local git repositories to. The executor keeps a local copy of every git repository it works with to speed operations and perform speculative merging. This should be on the same filesystem as :attr:`executor.job_dir` so that when git repos are cloned into the job workspaces, they can be hard-linked to the local git cache. .. attr:: job_dir :default: /tmp Directory that Zuul should use to hold temporary job directories. When each job is run, a new entry will be created under this directory to hold the configuration and scratch workspace for that job. It will be deleted at the end of the job (unless the `--keep-jobdir` command line option is specified). This should be on the same filesystem as :attr:`executor.git_dir` so that when git repos are cloned into the job workspaces, they can be hard-linked to the local git cache. .. attr:: log_config Path to log config file for the executor process. .. attr:: pidfile :default: /var/run/zuul-executor/zuul-executor.pid Path to PID lock file for the executor process. .. attr:: private_key_file :default: ~/.ssh/id_rsa SSH private key file to be used when logging into worker nodes. .. attr:: user :default: zuul 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. .. _admin_sitewide_variables: .. attr:: variables Path to an Ansible variables file to supply site-wide variables. This should be a YAML-formatted file consisting of a single dictionary. The contents will be made available to all jobs as Ansible variables. These variables take precedence over all other forms (job variables and secrets). Care should be taken when naming these variables to avoid potential collisions with those used by jobs. Prefixing variable names with a site-specific identifier is recommended. The default is not to add any site-wide variables. See the :ref:`User's Guide ` for more information. .. attr:: disk_limit_per_job :default: 250 This integer is the maximum number of megabytes that any one job is allowed to consume on disk while it is running. If a job's scratch space has more than this much space consumed, it will be aborted. .. attr:: trusted_ro_paths List of paths, separated by ``:`` to read-only bind mount into trusted bubblewrap contexts. .. attr:: trusted_rw_paths List of paths, separated by ``:`` to read-write bind mount into trusted bubblewrap contexts. .. attr:: untrusted_ro_paths List of paths, separated by ``:`` to read-only bind mount into untrusted bubblewrap contexts. .. attr:: untrusted_rw_paths List of paths, separated by ``:`` to read-write bind mount into untrusted bubblewrap contexts. .. attr:: merger .. attr:: git_user_email Value to pass to `git config user.email `_. .. attr:: git_user_name Value to pass to `git config user.name `_. 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``. Web Server ---------- The Zuul web server currently acts as a websocket interface to live log streaming. Eventually, it will serve as the single process handling all HTTP interactions with Zuul. Configuration ~~~~~~~~~~~~~ In addition to the common configuration sections, the following sections of ``zuul.conf`` are used by the web server: .. attr:: web .. attr:: listen_address :default: 127.0.0.1 IP address or domain name on which to listen. .. attr:: log_config Path to log config file for the web server process. .. attr:: pidfile :default: /var/run/zuul-web/zuul-web.pid Path to PID lock file for the web server process. .. attr:: port :default: 9000 Port to use for web server process. .. attr:: websocket_url Base URL on which the websocket service is exposed, if different than the base URL of the web app. Operation ~~~~~~~~~ To start the web server, run ``zuul-web``. To stop it, kill the PID which was saved in the pidfile specified in the configuration.