======= Plugins ======= The OpenStack ecosystem is wide and deep, and only growing more so every day. The value of DevStack is that it's simple enough to understand what it's doing clearly. And yet we'd like to support as much of the OpenStack Ecosystem as possible. We do that with plugins. DevStack plugins are bits of bash code that live outside the DevStack tree. They are called through a strong contract, so these plugins can be sure that they will continue to work in the future as DevStack evolves. Plugin Interface ================ DevStack supports a standard mechansim for including plugins from external repositories. The plugin interface assumes the following: An external git repository that includes a ``devstack/`` top level directory. Inside this directory there can be 2 files. - ``settings`` - a file containing global variables that will be sourced very early in the process. This is helpful if other plugins might depend on this one, and need access to global variables to do their work. Your settings should include any ``enable_service`` lines required by your plugin. This is especially important if you are kicking off services using ``run_process`` as it only works with enabled services. Be careful to allow users to override global-variables for customizing their environment. Usually it is best to provide a default value only if the variable is unset or empty; e.g. in bash syntax ``FOO=${FOO:-default}``. - ``plugin.sh`` - the actual plugin. It is executed by devstack at well defined points during a ``stack.sh`` run. The plugin.sh internal structure is discussed bellow. Plugins are registered by adding the following to the localrc section of ``local.conf``. They are added in the following format:: [[local|localrc]] enable_plugin [GITREF] - ``name`` - an arbitrary name. (ex: glustfs, docker, zaqar, congress) - ``giturl`` - a valid git url that can be cloned - ``gitref`` - an optional git ref (branch / ref / tag) that will be cloned. Defaults to master. An example would be as follows:: enable_plugin ec2api git://git.openstack.org/stackforge/ec2api plugin.sh contract ================== ``plugin.sh`` is a bash script that will be called at specific points during ``stack.sh``, ``unstack.sh``, and ``clean.sh``. It will be called in the following way:: source $PATH/TO/plugin.sh [phase] ``mode`` can be thought of as the major mode being called, currently one of: ``stack``, ``unstack``, ``clean``. ``phase`` is used by modes which have multiple points during their run where it's necessary to be able to execute code. All existing ``mode`` and ``phase`` points are considered **strong contracts** and won't be removed without a reasonable deprecation period. Additional new ``mode`` or ``phase`` points may be added at any time if we discover we need them to support additional kinds of plugins in devstack. The current full list of ``mode`` and ``phase`` are: - **stack** - Called by ``stack.sh`` four times for different phases of its run: - **pre-install** - Called after system (OS) setup is complete and before project source is installed. - **install** - Called after the layer 1 and 2 projects source and their dependencies have been installed. - **post-config** - Called after the layer 1 and 2 services have been configured. All configuration files for enabled services should exist at this point. - **extra** - Called near the end after layer 1 and 2 services have been started. - **unstack** - Called by ``unstack.sh`` before other services are shut down. - **clean** - Called by ``clean.sh`` before other services are cleaned, but after ``unstack.sh`` has been called. Example plugin ==================== An example plugin would look something as follows. ``devstack/settings``:: # settings file for template enable_service template ``devstack/plugin.sh``:: # plugin.sh - DevStack plugin.sh dispatch script template function install_template { ... } function init_template { ... } function configure_template { ... } # check for service enabled if is_service_enabled template; then if [[ "$1" == "stack" && "$2" == "pre-install" ]]; then # Set up system services echo_summary "Configuring system services Template" install_package cowsay elif [[ "$1" == "stack" && "$2" == "install" ]]; then # Perform installation of service source echo_summary "Installing Template" install_template elif [[ "$1" == "stack" && "$2" == "post-config" ]]; then # Configure after the other layer 1 and 2 services have been configured echo_summary "Configuring Template" configure_template elif [[ "$1" == "stack" && "$2" == "extra" ]]; then # Initialize and start the template service echo_summary "Initializing Template" init_template fi if [[ "$1" == "unstack" ]]; then # Shut down template services # no-op : fi if [[ "$1" == "clean" ]]; then # Remove state and transient data # Remember clean.sh first calls unstack.sh # no-op : fi fi Plugin Execution Order ====================== Plugins are run after in tree services at each of the stages above. For example, if you need something to happen before Keystone starts, you should do that at the ``post-config`` phase. Multiple plugins can be specified in your ``local.conf``. When that happens the plugins will be executed **in order** at each phase. This allows plugins to conceptually depend on each other through documenting to the user the order they must be declared. A formal dependency mechanism is beyond the scope of the current work. System Packages =============== Devstack provides a framework for getting packages installed at an early phase of its execution. This packages may be defined in a plugin as files that contain new-line separated lists of packages required by the plugin Supported packaging systems include apt and yum across multiple distributions. To enable a plugin to hook into this and install package dependencies, packages may be listed at the following locations in the top-level of the plugin repository: - ``./devstack/files/debs/$plugin_name`` - Packages to install when running on Ubuntu, Debian or Linux Mint. - ``./devstack/files/rpms/$plugin_name`` - Packages to install when running on Red Hat, Fedora, CentOS or XenServer. - ``./devstack/files/rpms-suse/$plugin_name`` - Packages to install when running on SUSE Linux or openSUSE. Using Plugins in the OpenStack Gate =================================== For everyday use, DevStack plugins can exist in any git tree that's accessible on the internet. However, when using DevStack plugins in the OpenStack gate, they must live in projects in OpenStack's gerrit. Both ``openstack`` namespace and ``stackforge`` namespace are fine. This allows testing of the plugin as well as provides network isolation against upstream git repository failures (which we see often enough to be an issue). Ideally a plugin will be included within the ``devstack`` directory of the project they are being tested. For example, the stackforge/ec2-api project has its pluggin support in its own tree. However, some times a DevStack plugin might be used solely to configure a backend service that will be used by the rest of OpenStack, so there is no "project tree" per say. Good examples include: integration of back end storage (e.g. ceph or glusterfs), integration of SDN controllers (e.g. ovn, OpenDayLight), or integration of alternate RPC systems (e.g. zmq, qpid). In these cases the best practice is to build a dedicated ``stackforge/devstack-plugin-FOO`` project. To enable a plugin to be used in a gate job, the following lines will be needed in your ``jenkins/jobs/.yaml`` definition in `project-config `_:: # Because we are testing a non standard project, add the # our project repository. This makes zuul do the right # reference magic for testing changes. export PROJECTS="stackforge/ec2-api $PROJECTS" # note the actual url here is somewhat irrelevant because it # caches in nodepool, however make it a valid url for # documentation purposes. export DEVSTACK_LOCAL_CONFIG="enable_plugin ec2-api git://git.openstack.org/stackforge/ec2-api" See Also ======== For additional inspiration on devstack plugins you can check out the `Plugin Registry `_.