253 lines
9.0 KiB
ReStructuredText
253 lines
9.0 KiB
ReStructuredText
=======
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Plugins
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=======
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The OpenStack ecosystem is wide and deep, and only growing more so
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every day. The value of DevStack is that it's simple enough to
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understand what it's doing clearly. And yet we'd like to support as
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much of the OpenStack Ecosystem as possible. We do that with plugins.
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DevStack plugins are bits of bash code that live outside the DevStack
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tree. They are called through a strong contract, so these plugins can
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be sure that they will continue to work in the future as DevStack
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evolves.
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Plugin Interface
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================
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DevStack supports a standard mechanism for including plugins from
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external repositories. The plugin interface assumes the following:
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An external git repository that includes a ``devstack/`` top level
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directory. Inside this directory there can be 3 files.
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- ``override-defaults`` - a file containing global variables that
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will be sourced before the lib/* files. This allows the plugin
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to override the defaults that are otherwise set in the lib/*
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files.
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For example, override-defaults may export CINDER_ENABLED_BACKENDS
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to include the plugin-specific storage backend and thus be able
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to override the default lvm only storage backend for Cinder.
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- ``settings`` - a file containing global variables that will be
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sourced very early in the process. This is helpful if other plugins
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might depend on this one, and need access to global variables to do
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their work.
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Your settings should include any ``enable_service`` lines required
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by your plugin. This is especially important if you are kicking off
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services using ``run_process`` as it only works with enabled
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services.
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Be careful to allow users to override global-variables for
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customizing their environment. Usually it is best to provide a
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default value only if the variable is unset or empty; e.g. in bash
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syntax ``FOO=${FOO:-default}``.
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- ``plugin.sh`` - the actual plugin. It is executed by devstack at
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well defined points during a ``stack.sh`` run. The plugin.sh
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internal structure is discussed below.
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Plugins are registered by adding the following to the localrc section
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of ``local.conf``.
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They are added in the following format::
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[[local|localrc]]
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enable_plugin <NAME> <GITURL> [GITREF]
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- ``name`` - an arbitrary name. (ex: glusterfs, docker, zaqar, congress)
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- ``giturl`` - a valid git url that can be cloned
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- ``gitref`` - an optional git ref (branch / ref / tag) that will be
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cloned. Defaults to master.
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An example would be as follows::
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enable_plugin ec2-api git://git.openstack.org/openstack/ec2-api
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plugin.sh contract
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==================
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``plugin.sh`` is a bash script that will be called at specific points
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during ``stack.sh``, ``unstack.sh``, and ``clean.sh``. It will be
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called in the following way::
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source $PATH/TO/plugin.sh <mode> [phase]
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``mode`` can be thought of as the major mode being called, currently
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one of: ``stack``, ``unstack``, ``clean``. ``phase`` is used by modes
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which have multiple points during their run where it's necessary to
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be able to execute code. All existing ``mode`` and ``phase`` points
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are considered **strong contracts** and won't be removed without a
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reasonable deprecation period. Additional new ``mode`` or ``phase``
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points may be added at any time if we discover we need them to support
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additional kinds of plugins in devstack.
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The current full list of ``mode`` and ``phase`` are:
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- **stack** - Called by ``stack.sh`` four times for different phases
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of its run:
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- **pre-install** - Called after system (OS) setup is complete and
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before project source is installed.
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- **install** - Called after the layer 1 and 2 projects source and
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their dependencies have been installed.
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- **post-config** - Called after the layer 1 and 2 services have
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been configured. All configuration files for enabled services
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should exist at this point.
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- **extra** - Called near the end after layer 1 and 2 services have
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been started.
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- **test-config** - Called at the end of devstack used to configure tempest
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or any other test environments
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- **unstack** - Called by ``unstack.sh`` before other services are shut
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down.
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- **clean** - Called by ``clean.sh`` before other services are cleaned,
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but after ``unstack.sh`` has been called.
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Example plugin
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====================
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An example plugin would look something as follows.
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``devstack/settings``::
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# settings file for template
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enable_service template
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``devstack/plugin.sh``::
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# plugin.sh - DevStack plugin.sh dispatch script template
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function install_template {
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...
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}
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function init_template {
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...
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}
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function configure_template {
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...
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}
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# check for service enabled
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if is_service_enabled template; then
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if [[ "$1" == "stack" && "$2" == "pre-install" ]]; then
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# Set up system services
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echo_summary "Configuring system services Template"
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install_package cowsay
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elif [[ "$1" == "stack" && "$2" == "install" ]]; then
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# Perform installation of service source
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echo_summary "Installing Template"
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install_template
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elif [[ "$1" == "stack" && "$2" == "post-config" ]]; then
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# Configure after the other layer 1 and 2 services have been configured
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echo_summary "Configuring Template"
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configure_template
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elif [[ "$1" == "stack" && "$2" == "extra" ]]; then
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# Initialize and start the template service
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echo_summary "Initializing Template"
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init_template
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fi
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if [[ "$1" == "unstack" ]]; then
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# Shut down template services
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# no-op
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:
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fi
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if [[ "$1" == "clean" ]]; then
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# Remove state and transient data
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# Remember clean.sh first calls unstack.sh
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# no-op
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:
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fi
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fi
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Plugin Execution Order
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======================
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Plugins are run after in tree services at each of the stages
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above. For example, if you need something to happen before Keystone
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starts, you should do that at the ``post-config`` phase.
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Multiple plugins can be specified in your ``local.conf``. When that
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happens the plugins will be executed **in order** at each phase. This
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allows plugins to conceptually depend on each other through
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documenting to the user the order they must be declared. A formal
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dependency mechanism is beyond the scope of the current work.
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System Packages
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===============
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Devstack provides a framework for getting packages installed at an early
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phase of its execution. These packages may be defined in a plugin as files
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that contain new-line separated lists of packages required by the plugin
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Supported packaging systems include apt and yum across multiple distributions.
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To enable a plugin to hook into this and install package dependencies, packages
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may be listed at the following locations in the top-level of the plugin
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repository:
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- ``./devstack/files/debs/$plugin_name`` - Packages to install when running
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on Ubuntu, Debian or Linux Mint.
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- ``./devstack/files/rpms/$plugin_name`` - Packages to install when running
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on Red Hat, Fedora, CentOS or XenServer.
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- ``./devstack/files/rpms-suse/$plugin_name`` - Packages to install when
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running on SUSE Linux or openSUSE.
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Using Plugins in the OpenStack Gate
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===================================
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For everyday use, DevStack plugins can exist in any git tree that's
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accessible on the internet. However, when using DevStack plugins in
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the OpenStack gate, they must live in projects in OpenStack's
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gerrit. This allows testing of the plugin as well as provides network
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isolation against upstream git repository failures (which we see often
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enough to be an issue).
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Ideally a plugin will be included within the ``devstack`` directory of
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the project they are being tested. For example, the openstack/ec2-api
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project has its plugin support in its own tree.
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However, some times a DevStack plugin might be used solely to
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configure a backend service that will be used by the rest of
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OpenStack, so there is no "project tree" per say. Good examples
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include: integration of back end storage (e.g. ceph or glusterfs),
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integration of SDN controllers (e.g. ovn, OpenDayLight), or
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integration of alternate RPC systems (e.g. zmq, qpid). In these cases
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the best practice is to build a dedicated
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``openstack/devstack-plugin-FOO`` project.
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To enable a plugin to be used in a gate job, the following lines will
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be needed in your ``jenkins/jobs/<project>.yaml`` definition in
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`project-config
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<http://git.openstack.org/cgit/openstack-infra/project-config/>`_::
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# Because we are testing a non standard project, add the
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# our project repository. This makes zuul do the right
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# reference magic for testing changes.
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export PROJECTS="openstack/ec2-api $PROJECTS"
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# note the actual url here is somewhat irrelevant because it
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# caches in nodepool, however make it a valid url for
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# documentation purposes.
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export DEVSTACK_LOCAL_CONFIG="enable_plugin ec2-api git://git.openstack.org/openstack/ec2-api"
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See Also
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========
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For additional inspiration on devstack plugins you can check out the
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`Plugin Registry <plugin-registry.html>`_.
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