HACKING.rst

Contributing to DevStack
========================


General
-------

DevStack is written in UNIX shell script.  It uses a number of bash-isms
and so is limited to Bash (version 4 and up) and compatible shells.
Shell script was chosen because it best illustrates the steps used to
set up and interact with OpenStack components.

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

Contributing code to DevStack follows the usual OpenStack process as described
in `How To Contribute`__ in the OpenStack wiki.  `DevStack's LaunchPad project`__
contains the usual links for blueprints, bugs, etc.

__ contribute_
.. _contribute: http://docs.openstack.org/infra/manual/developers.html

__ lp_
.. _lp: https://launchpad.net/~devstack

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.

The ``lib`` directory contains sub-scripts for projects or packages that ``stack.sh``
sources to perform much of the work related to those projects.  These sub-scripts
contain configuration defaults and functions to configure, start and stop the project
or package.  These variables and functions are also used by related projects,
such as Grenade, to manage a DevStack installation.

A number of additional scripts can be found in the ``tools`` directory that may
be useful in supporting DevStack installations.  Of particular note are ``info.sh``
to collect and report information about the installed system, and ``install_prereqs.sh``
that handles installation of the prerequisite packages for DevStack.  It is
suitable, for example, to pre-load a system for making a snapshot.


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.  It has been broken down into project-specific subscripts (as noted above)
located in ``lib`` to make ``stack.sh`` more manageable and to promote code reuse.

These library sub-scripts have a number of fixed entry points, some of which may
just be stubs.  These entry points will be called by ``stack.sh`` in the
following order::

    install_XXXX
    configure_XXXX
    init_XXXX
    start_XXXX
    stop_XXXX
    cleanup_XXXX

There is a sub-script template in ``lib/templates`` to be used in creating new
service sub-scripts.  The comments in ``<>`` are meta comments describing
how to use the template and should be removed.

In order to show the dependencies and conditions under which project functions
are executed the top-level conditional testing for things like ``is_service_enabled``
should be done in ``stack.sh``.  There may be nested conditionals that need
to be in the sub-script, such as testing for keystone being enabled in
``configure_swift()``.


stackrc
-------

``stackrc`` is the global configuration file for DevStack.  It is responsible for
calling ``local.conf`` (or ``localrc`` if it exists) so local user configuration
is recognized.

The criteria for what belongs in ``stackrc`` can be vaguely summarized as
follows:

* All project repositories and branches handled directly in ``stack.sh``
* Global configuration that may be referenced in ``local.conf``, i.e. ``DEST``, ``DATA_DIR``
* Global service configuration like ``ENABLED_SERVICES``
* Variables used by multiple services that do not have a clear owner, i.e.
  ``VOLUME_BACKING_FILE_SIZE`` (nova-compute, nova-volumes and cinder) or
  ``PUBLIC_NETWORK_NAME`` (nova-network and neutron)
* Variables that can not be cleanly declared in a project file due to
  dependency ordering, i.e. the order of sourcing the project files can
  not be changed for other reasons but the earlier file needs to dereference a
  variable set in the later file.  This should be rare.

Also, variable declarations in ``stackrc`` before ``local.conf`` is sourced
do NOT allow overriding (the form
``FOO=${FOO:-baz}``); if they did then they can already be changed in ``local.conf``
and can stay in the project file.


Documentation
-------------

The DevStack repo now contains all of the static pages of devstack.org in
the ``doc/source`` directory. The OpenStack CI system rebuilds the docs after every
commit and updates devstack.org (now a redirect to docs.openstack.org/developer/devstack).

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.

.. _shocco: https://github.com/dtroyer/shocco/tree/rst_support

The script used to drive <code>shocco</code> is <code>tools/build_docs.sh</code>.
The complete docs build is also handled with <code>tox -edocs</code> per the
OpenStack project standard.


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 occurred.
    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.

.. _CLIAuth: http://wiki.openstack.org/CLIAuth

* 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.


Bash Style Guidelines
~~~~~~~~~~~~~~~~~~~~~
DevStack defines a bash set of best practices for maintaining large
collections of bash scripts. These should be considered as part of the
review process.

DevStack uses the bashate_ style checker
to enforce basic guidelines, similar to pep8 and flake8 tools for Python. The
list below is not complete for what bashate checks, nor is it all checked
by bashate.  So many lines of code, so little time.

.. _bashate: https://pypi.python.org/pypi/bashate

Whitespace Rules
----------------

- lines should not include trailing whitespace
- there should be no hard tabs in the file
- indents are 4 spaces, and all indentation should be some multiple of
  them

Control Structure Rules
-----------------------
- then should be on the same line as the if
- do should be on the same line as the for

Example::

  if [[ -r $TOP_DIR/local.conf ]]; then
      LRC=$(get_meta_section_files $TOP_DIR/local.conf local)
      for lfile in $LRC; do
          if [[ "$lfile" == "localrc" ]]; then
              if [[ -r $TOP_DIR/localrc ]]; then
                  warn $LINENO "localrc and local.conf:[[local]] both exist, using localrc"
              else
                  echo "# Generated file, do not edit" >$TOP_DIR/.localrc.auto
                  get_meta_section $TOP_DIR/local.conf local $lfile >>$TOP_DIR/.localrc.auto
              fi
          fi
      done
  fi

Variables and Functions
-----------------------
- functions should be used whenever possible for clarity
- functions should use ``local`` variables as much as possible to
  ensure they are isolated from the rest of the environment
- local variables should be lower case, global variables should be
  upper case
- function names should_have_underscores, NotCamelCase.
- functions should be declared as per the regex ^function foo {$
  with code starting on the next line