devstack/HACKING.rst

Contributing to DevStack

General

DevStack is written in POSIX shell script. This choice was made because it best illustrates the configuration steps that this implementation takes on setting up and interacting with OpenStack components. DevStack specifies BASH and is compatible with Bash 3.

DevStack's official repository is located on GitHub at https://github.com/openstack-dev/devstack.git. Besides the master branch that tracks the OpenStack trunk branches a separate branch is maintained for all OpenStack releases starting with Diablo (stable/diablo).

The primary script in DevStack is stack.sh, which performs the bulk of the work for DevStack's use cases. There is a subscript functions that contains generally useful shell functions and is used by a number of the scripts in DevStack.

A number of additional scripts can be found in the tools directory that may be useful in setting up special-case uses of DevStack. These include: bare metal deployment, ramdisk deployment and Jenkins integration.

Scripts

DevStack scripts should generally begin by calling env(1) in the shebang line:

#!/usr/bin/env bash

Sometimes the script needs to know the location of the DevStack install directory. TOP_DIR should always point there, even if the script itself is located in a subdirectory:

# Keep track of the current devstack directory.
TOP_DIR=$(cd $(dirname "$0") && pwd)

Many scripts will utilize shared functions from the functions file. There are also rc files (stackrc and openrc) that are often included to set the primary configuration of the user environment:

# Keep track of the current devstack directory.
TOP_DIR=$(cd $(dirname "$0") && pwd)

# Import common functions
source $TOP_DIR/functions

# Import configuration
source $TOP_DIR/openrc

stack.sh is a rather large monolithic script that flows through from beginning to end. There is a proposal to segment it to put the OpenStack projects into their own sub-scripts to better document the projects as a unit rather than have it scattered throughout stack.sh. Someday.

Documentation

The official DevStack repo on GitHub does not include a gh-pages branch that GitHub uses to create static web sites. That branch is maintained in the CloudBuilders DevStack repo mirror that supports the http://devstack.org site. This is the primary DevStack documentation along with the DevStack scripts themselves.

All of the scripts are processed with shocco to render them with the comments as text describing the script below. For this reason we tend to be a little verbose in the comments _ABOVE the code they pertain to. Shocco also supports Markdown formatting in the comments; use it sparingly. Specifically, stack.sh uses Markdown headers to divide the script into logical sections.

Exercises

The scripts in the exercises directory are meant to 1) perform basic operational checks on certain aspects of OpenStack; and b) document the use of the OpenStack command-line clients.

In addition to the guidelines above, exercise scripts MUST follow the structure outlined here. swift.sh is perhaps the clearest example of these guidelines. These scripts are executed serially by exercise.sh in testing situations.

• Begin and end with a banner that stands out in a sea of script logs to aid in debugging failures, particularly in automated testing situations. If the end banner is not displayed, the script ended prematurely and can be assumed to have failed.

  echo "**************************************************"
  echo "Begin DevStack Exercise: $0"
  echo "**************************************************"
  ...
  set +o xtrace
  echo "**************************************************"
  echo "End DevStack Exercise: $0"
  echo "**************************************************"

• The scripts will generally have the shell xtrace attribute set to display the actual commands being executed, and the errexit attribute set to exit the script on non-zero exit codes:

  # This script exits on an error so that errors don't compound and you see
  # only the first error that occured.
  set -o errexit
  
  # Print the commands being run so that we can see the command that triggers
  # an error.  It is also useful for following allowing as the install occurs.
  set -o xtrace

• Settings and configuration are stored in exerciserc, which must be sourced after openrc or stackrc:

  # Import exercise configuration
  source $TOP_DIR/exerciserc

• There are a couple of helper functions in the common functions sub-script that will check for non-zero exit codes and unset environment variables and print a message and exit the script. These should be called after most client commands that are not otherwise checked to short-circuit long timeouts (instance boot failure, for example):

  swift post $CONTAINER
  die_if_error "Failure creating container $CONTAINER"
  
  FLOATING_IP=`euca-allocate-address | cut -f2`
  die_if_not_set FLOATING_IP "Failure allocating floating IP"

• If you want an exercise to be skipped when for example a service wasn't enabled for the exercise to be run, you can exit your exercise with the special exitcode 55 and it will be detected as skipped.

• The exercise scripts should only use the various OpenStack client binaries to interact with OpenStack. This specifically excludes any *-manage tools as those assume direct access to configuration and databases, as well as direct database access from the exercise itself.

• If specific configuration needs to be present for the exercise to complete, it should be staged in stack.sh, or called from stack.sh (see files/keystone_data.sh for an example of this).

• The OS_* environment variables should be the only ones used for all authentication to OpenStack clients as documented in the CLIAuth wiki page.

• The exercise MUST clean up after itself if successful. If it is not successful, it is assumed that state will be left behind; this allows a chance for developers to look around and attempt to debug the problem. The exercise SHOULD clean up or graciously handle possible artifacts left over from previous runs if executed again. It is acceptable to require a reboot or even a re-install of DevStack to restore a clean test environment.