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: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
Finger -- Gearman
Gearman -- Scheduler;
Scheduler -- Gerrit;
Scheduler -- Zookeeper;
Zookeeper -- Nodepool;
Scheduler -- GitHub;
}
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.
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.
If statsd is enabled, every service 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.
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
[web]
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.
.. attr:: statsd
Information about the optional statsd server. If the ``statsd``
python module is installed and this section is configured,
statistics will be reported to statsd. See :ref:`statsd` for more
information.
.. attr:: server
Hostname or IP address of the statsd server.
.. attr:: port
:default: 8125
The UDP port on which the statsd server is listening.
.. attr:: prefix
If present, this will be prefixed to all of the keys before
transmitting to the statsd server.
.. 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.
.. attr:: session_timeout
:default: 10.0
The ZooKeeper session timeout, in seconds.
.. _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.
The scheduler includes a Gearman server which is used to communicate
with other components of Zuul. It is possible to use an external
Gearman server, but the built-in server is well-tested and
recommended. If the built-in server is used, other Zuul hosts will
need to be able to connect to the scheduler on the Gearman port, TCP
port 4730. It is also strongly recommended to use SSL certs with
Gearman, as secrets are transferred from the scheduler to executors
over this link.
The scheduler must be able to connect to the ZooKeeper cluster used by
Nodepool in order to request nodes. It does not need to connect
directly to the nodes themselves, however -- that function is handled
by the Executors.
It must also be able to connect to any services for which connections
are configured (Gerrit, GitHub, etc).
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:: port
:default: 4730
TCP port 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:: web
.. 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:: command_socket
:default: /var/lib/zuul/scheduler.socket
Path to command socket file for the scheduler process.
.. attr:: tenant_config
Path to :ref:`tenant-config` file. This attribute
is exclusive with :attr:`scheduler.tenant_config_script`.
.. attr:: tenant_config_script
Path to a script to execute and load the tenant
config from. This attribute is exclusive with
:attr:`scheduler.tenant_config`.
.. attr:: log_config
Path to log config file.
.. attr:: pidfile
:default: /var/run/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, run
``zuul-scheduler full-reconfigure``. The signal based method by sending
a `SIGHUP` signal to the scheduler PID is deprecated.
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.
Mergers need to be able to connect to the Gearman server (usually the
scheduler host) as well as any services for which connections are
configured (Gerrit, GitHub, etc).
Configuration
~~~~~~~~~~~~~
The following section of ``zuul.conf`` is used by the merger:
.. attr:: merger
.. attr:: command_socket
:default: /var/lib/zuul/merger.socket
Path to command socket file for the merger process.
.. attr:: git_dir
:default: /var/lib/zuul/merger-git
Directory in which Zuul should clone git repositories.
.. attr:: git_http_low_speed_limit
:default: 1000
If the HTTP transfer speed is less then git_http_low_speed_limit for
longer then git_http_low_speed_time, the transfer is aborted.
Value in bytes, setting to 0 will disable.
.. attr:: git_http_low_speed_time
:default: 30
If the HTTP transfer speed is less then git_http_low_speed_limit for
longer then git_http_low_speed_time, the transfer is aborted.
Value in seconds, setting to 0 will disable.
.. attr:: git_user_email
Value to pass to `git config user.email
<https://git-scm.com/book/en/v2/Getting-Started-First-Time-Git-Setup>`_.
.. attr:: git_user_name
Value to pass to `git config user.name
<https://git-scm.com/book/en/v2/Getting-Started-First-Time-Git-Setup>`_.
.. attr:: log_config
Path to log config file for the merger process.
.. attr:: pidfile
:default: /var/run/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.
Executors need to be able to connect to the Gearman server (usually
the scheduler host), any services for which connections are configured
(Gerrit, GitHub, etc), as well as directly to the hosts which Nodepool
provides.
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`_ [#nullwrap]_ 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
.. _zuul-discuss: http://lists.zuul-ci.org/cgi-bin/mailman/listinfo/zuul-discuss
.. [#nullwrap] `bubblewrap` is integral to securely operating Zuul.
If it is difficult for you to use it in your environment, we
encourage you to let us know via the `zuul-discuss`_ mailing
list.
Configuration
~~~~~~~~~~~~~
The following sections of ``zuul.conf`` are used by the executor:
.. attr:: executor
.. attr:: command_socket
:default: /var/lib/zuul/executor.socket
Path to command socket file for the executor process.
.. attr:: finger_port
:default: 7900
Port to use for finger log streamer.
.. attr:: state_dir
:default: /var/lib/zuul
Path to directory in which Zuul should save its state.
.. attr:: git_dir
:default: /var/lib/zuul/executor-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.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:: default_username
:default: zuul
Username to use when logging into worker nodes, if none is
supplied by Nodepool.
.. attr:: winrm_cert_key_file
:default: ~/.winrm/winrm_client_cert.key
The private key file of the client certificate to use for winrm
connections to Windows nodes.
.. attr:: winrm_cert_pem_file
:default: ~/.winrm/winrm_client_cert.pem
The certificate file of the client certificate to use for winrm
connections to Windows nodes.
.. note:: Currently certificate verification is disabled when
connecting to Windows nodes via winrm.
.. _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
<user_jobs_sitewide_variables>` 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:: load_multiplier
:default: 2.5
When an executor host gets too busy, the system may suffer
timeouts and other ill effects. The executor will stop accepting
more than 1 job at a time until load has lowered below a safe
level. This level is determined by multiplying the number of
CPU's by `load_multiplier`.
So for example, if the system has 2 CPUs, and load_multiplier
is 2.5, the safe load for the system is 5.00. Any time the
system load average is over 5.00, the executor will quit
accepting multiple jobs at one time.
The executor will observe system load and determine whether
to accept more jobs every 30 seconds.
.. attr:: min_avail_hdd
:default: 5.0
This is the minimum percentage of HDD storage available for the
:attr:`executor.state_dir` directory. The executor will stop accepting
more than 1 job at a time until more HDD storage is available. The
available HDD percentage is calculated from the total available
disk space divided by the total real storage capacity multiplied by
100.
.. attr:: min_avail_mem
:default: 5.0
This is the minimum percentage of system RAM available. The
executor will stop accepting more than 1 job at a time until
more memory is available. The available memory percentage is
calculated from the total available memory divided by the
total real memory multiplied by 100. Buffers and cache are
considered available in the calculation.
.. attr:: hostname
:default: hostname of the server
The executor needs to know its hostname under which it is reachable by
zuul-web. Otherwise live console log streaming doesn't work. In most cases
This is automatically detected correctly. But when running in environments
where it cannot determine its hostname correctly this can be overridden
here.
.. attr:: zone
:default: None
Name of the nodepool executor-zone to exclusively execute all jobs that
have nodes of the specified provider. As an example, it is possible for
nodepool nodes to exist in a cloud with out public accessable IP
IP address. By adding an executor to a zone nodepool nodes could be
configured to use private ip addresses.
To enable this in nodepool, you'll use the node-attributes setting in a
provider pool. For example:
.. code-block:: yaml
pools:
- name: main
node-attributes:
executor-zone: vpn
.. attr:: merger
.. attr:: git_user_email
Value to pass to `git config user.email
<https://git-scm.com/book/en/v2/Getting-Started-First-Time-Git-Setup>`_.
.. attr:: git_user_name
Value to pass to `git config user.name
<https://git-scm.com/book/en/v2/Getting-Started-First-Time-Git-Setup>`_.
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.
In order to stop the executor and under normal circumstances it is
best to pause and wait for all currently running jobs to finish
before stopping it. To do so run ``zuul-executor pause``.
To stop the executor immediately, run ``zuul-executor stop``. Jobs that were
running on the stopped executor will be rescheduled on other executors.
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
----------
.. TODO: Turn REST API into a link to swagger docs when we grow them
The Zuul web server serves as the single process handling all HTTP
interactions with Zuul. This includes the websocket interface for live
log streaming, the REST API and the html/javascript dashboard. All three are
served as a holistic web application. For information on additional supported
deployment schemes, see :ref:`web-deployment-options`.
Web servers need to be able to connect to the Gearman server (usually
the scheduler host). If the SQL reporter is used, they need to be
able to connect to the database it reports to in order to support the
dashboard. If a GitHub connection is configured, they need to be
reachable by GitHub so they may receive notifications.
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.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.
.. attr:: stats_url
Base URL from which statistics emitted via statsd can be queried.
.. attr:: stats_type
:default: graphite
Type of server hosting the statistics information. Currently only
'graphite' is supported by the dashboard.
.. attr:: static_path
:default: zuul/web/static
Path containing the static web assets.
.. attr:: static_cache_expiry
:default: 3600
The Cache-Control max-age response header value for static files served
by the zuul-web. Set to 0 during development to disable Cache-Control.
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.
Finger Gateway
--------------
The Zuul finger gateway listens on the standard finger port (79) for
finger requests specifying a build UUID for which it should stream log
results. The gateway will determine which executor is currently running that
build and query that executor for the log stream.
This is intended to be used with the standard finger command line client.
For example::
finger UUID@zuul.example.com
The above would stream the logs for the build identified by `UUID`.
Finger gateway servers need to be able to connect to the Gearman
server (usually the scheduler host), as well as the console streaming
port on the executors (usually 7900).
Configuration
~~~~~~~~~~~~~
In addition to the common configuration sections, the following
sections of ``zuul.conf`` are used by the finger gateway:
.. attr:: fingergw
.. attr:: command_socket
:default: /var/lib/zuul/fingergw.socket
Path to command socket file for the executor process.
.. attr:: listen_address
:default: all addresses
IP address or domain name on which to listen.
.. attr:: log_config
Path to log config file for the finger gateway process.
.. attr:: pidfile
:default: /var/run/zuul/fingergw.pid
Path to PID lock file for the finger gateway process.
.. attr:: port
:default: 79
Port to use for the finger gateway. Note that since command line
finger clients cannot usually specify the port, leaving this set to
the default value is highly recommended.
.. attr:: user
:default: zuul
User ID for the zuul-fingergw process. In normal operation as a
daemon, the finger gateway should be started as the ``root`` user, but
it will drop privileges to this user during startup.
Operation
~~~~~~~~~
To start the finger gateway, run ``zuul-fingergw``. To stop it, kill the
PID which was saved in the pidfile specified in the configuration.
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