cdist/doc/man/cdist-type.text

cdist-type(7)
=============
Nico Schottelius <nico-cdist--@--schottelius.org>


NAME
----
cdist-type - Functionality bundled


SYNOPSIS
--------
__TYPE ID --parameter value [--parameter value ...]

__TYPE --parameter value [--parameter value ...] (for singletons)


DESCRIPTION
-----------
Types are the main component of cdist and define functionality. If you
use cdist, you'll write a type for every functionality you would like
to use.


HOW TO USE A TYPE
-----------------
You can use types from the initial manifest or the type manifest like a
normal command:

--------------------------------------------------------------------------------
# Creates empty file /etc/cdist-configured
__file /etc/cdist-configured --type file

# Ensure tree is installed
__package tree --state installed
--------------------------------------------------------------------------------

Internally cdist-type-emulator(1) will be called from cdist-manifest-run(1) to
save the given parameters into a cconfig database, so they can be accessed by
the manifest and gencode scripts of the type (see below).

A list of supported types can be found in the cdist-reference(7) manpage.

SINGLETON TYPES
---------------
If a type is flagged as a singleton, it may me used only once. This
is useful for types which can be used only once on a system. If a type
can only be used once, it does not take an 

Example:
--------------------------------------------------------------------------------
# __issue type manages /etc/issue
__issue

# Probably your own type - singletons may use parameters
__myfancysingleton --colour green
--------------------------------------------------------------------------------



HOW TO WRITE A NEW TYPE
-----------------------
A type consists of

- parameter (optional)
- manifest  (optional)
- singleton (optional)
- explorer  (optional)
- gencode   (optional)

Types are stored below conf/type/. Their name should always be prefixed with
two underscores (__) to prevent collisions with other binaries in $PATH.

To begin a new type from a template, execute "cdist-type-template __NAME"
and cd conf/type/__NAME.


DEFINING PARAMETERS
-------------------
Every type consists of optional and required parameters, which must
be created in a newline seperated file in parameters/required and
parameters/optional. If either or both missing, the type will have
no required, no optional or no parameters at all.

Example:
--------------------------------------------------------------------------------
echo servername >> conf/type/__nginx_vhost/parameter/required
echo logdirectory >> conf/type/__nginx_vhost/parameter/optional
--------------------------------------------------------------------------------


WRITING THE MANIFEST
--------------------
In the manifest of a type you can use other types, so your type extends
their functionality. A good example is the __package type, which in
a shortened version looks like this:

--------------------------------------------------------------------------------
os="$(cat "$__global/explorer/os")"
case "$os" in
      archlinux) type="pacman" ;;
      debian|ubuntu) type="apt" ;;
      gentoo) type="emerge" ;;
      *)
         echo "Don't know how to manage packages on: $os" >&2
         exit 1
      ;;
esac

__package_$type "$@"
--------------------------------------------------------------------------------

As you can see, the type can reference different environment variables,
which are documented in cdist-environment-variables(7).

Always ensure the manifest is executable, otherwise cdist will not be able
to execute it.


SINGLETON - ONLY INSTANCE ONLY
------------------------------
If you want to ensure that a type can only be used once per target, you can
mark it as a singleton: Just create the (empty) file "singleton" in your type
directory. This will also change the way your type must be called:

--------------------------------------------------------------------------------
__YOURTYPE --parameter value
--------------------------------------------------------------------------------

As you can see, the ID is omitted, because it does not make any sense, if your
type can be used only once.


THE TYPE EXPLORERS
------------------
If a type needs to explore specific details, it can provide type specific
explorers, which will be executed on the target for every created object.

The explorers are stored under the "explorer" directory below the type.
It could for instance contain code to check the md5sum of a file on the
client, like this (shortened version from real type __file):

--------------------------------------------------------------------------------
if [ -f "$__object/parameter/destination" ]; then
   destination="$(cat "$__object/parameter/destination")"
else
   destination="/$__object_id"
fi

if [ -e "$destination" ]; then
   md5sum < "$destination"
fi
--------------------------------------------------------------------------------


WRITING THE GENCODE SCRIPT
--------------------------
There are two gencode scripts: gencode-local and gencode-remote.
The output of gencode-local is executed locally, whereas
the output of gencode-remote is executed on the target.

The gencode script can make use of the parameters, the global explorers
and the type specific explorers. The output (stdout) of this script is
saved by cdist and will be executed on the target.

If the gencode script encounters an error, it should print diagnostic
messages to stderr and exit non-zero. If you need to debug the gencode
script, you can write to stderr:

--------------------------------------------------------------------------------
# Debug output to stderr
echo "My fancy debug line" >&2

# Output to be saved by cdist for execution on the target
echo "touch /etc/cdist-configured"
--------------------------------------------------------------------------------


HINTS FOR TYPEWRITERS
----------------------
It must be assumed that the target is pretty dumb and thus does not have high
level tools like ruby installed. If a type requires specific tools to be present
on the target, there must be another type that provides this tool and the first
type should create an object of the specific type.

If your type wants to save temporay data, that may be used by other types
later on (for instance __file), you can save them in the subdirectory
"files" below $__object (but you must create it yourself). cdist will not touch
this directory.

If your type contains static files, it's also recommened to place them in
a folder named "files" within the type (again, because cdist guarantees to
never ever touch this folder).

HOW TO INCLUDE A TYPE INTO UPSTREAM CDIST
-----------------------------------------
If you think your type may be useful for others, ensure it works with the
current master branch of cdist and submit the git url containing the type for
inclusion to the mailinglist **cdist at cdist -- at -- l.schottelius.org**.

Ensure a corresponding manpage named man.text in asciidoc format with
the manpage-name "cdist-type__NAME" is included in the type directory.


SEE ALSO
--------
- cdist-manifest-run(1)
- cdist-stages(7)


COPYING
-------
Copyright \(C) 2011 Nico Schottelius. Free use of this software is
granted under the terms of the GNU General Public License version 3 (GPLv3).