devstack/extras.d/README.md

Extras Hooks

The extras.d directory contains project dispatch scripts that are called at specific times by stack.sh, unstack.sh and clean.sh. These hooks are used to install, configure and start additional projects during a DevStack run without any modifications to the base DevStack scripts.

When stack.sh reaches one of the hook points it sources the scripts in extras.d that end with .sh. To control the order that the scripts are sourced their names start with a two digit sequence number. DevStack reserves the sequence numbers 00 through 09 and 90 through 99 for its own use.

The scripts are sourced at the beginning of each script that calls them. The entire stack.sh variable space is available. The scripts are sourced with one or more arguments, the first of which defines the hook phase:

source | stack | unstack | clean

source: always called first in any of the scripts, used to set the
    initial defaults in a lib/* script or similar

stack: called by stack.sh.  There are four possible values for
    the second arg to distinguish the phase stack.sh is in:

    arg 2:  install | post-config | extra | post-extra

unstack: called by unstack.sh

clean: called by clean.sh.  Remember, clean.sh also calls unstack.sh
    so that work need not be repeated.