devstack/doc/source/plugins.rst

Plugins

DevStack has a couple of plugin mechanisms to allow easily adding support for additional projects and features.

Extras.d Hooks

These hooks are an extension of the service calls in stack.sh at specific points in its run, plus unstack.sh and clean.sh. A number of the higher-layer projects are implemented in DevStack using this mechanism.

The script in extras.d is expected to be mostly a dispatcher to functions in a lib/* script. The scripts are named with a zero-padded two digits sequence number prefix to control the order that the scripts are called, and with a suffix of .sh. DevStack reserves for itself the sequence numbers 00 through 09 and 90 through 99.

Below is a template that shows handlers for the possible command-line arguments:

# template.sh - DevStack extras.d dispatch script template

# check for service enabled
if is_service_enabled template; then

    if [[ "$1" == "source" ]]; then
        # Initial source of lib script
        source $TOP_DIR/lib/template
    fi

    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

The arguments are:

• source - Called by each script that utilizes extras.d hooks; this replaces directly sourcing the lib/* script.
• stack - Called by stack.sh three 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. This is the existing hook and has not otherwise changed.
• 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.

Externally Hosted Plugins

Based on the extras.d hooks, 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.
• plugin.sh - the actual plugin. It will be executed by devstack during it's run. The run order will be done in the registration order for these plugins, and will occur immediately after all in tree extras.d dispatch at the phase in question. The plugin.sh looks like the extras.d dispatcher above except it should not include the is_service_enabled conditional. All external plugins are always assumed to be enabled.

Plugins are registered by adding the following to the localrc section of local.conf.

They are added in the following format:

enable_plugin <NAME> <GITURL> [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 glusterfs https://github.com/sdague/devstack-plugins glusterfs

Hypervisor

Hypervisor plugins are fairly new and condense most hypervisor configuration into one place.

The initial plugin implemented was for Docker support and is a useful template for the required support. Plugins are placed in lib/nova_plugins and named hypervisor-<name> where <name> is the value of VIRT_DRIVER. Plugins must define the following functions:

• install_nova_hypervisor - install any external requirements
• configure_nova_hypervisor - make configuration changes, including those to other services
• start_nova_hypervisor - start any external services
• stop_nova_hypervisor - stop any external services
• cleanup_nova_hypervisor - remove transient data and cache