docs/man -> docs/src and update Makefile and build-helper.
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Darko Poljak
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297
docs/src/cdist-type.rst
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297
docs/src/cdist-type.rst
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cdist type
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==========
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Description
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-----------
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Types are the main component of cdist and define functionality. If you
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use cdist, you'll write a type for every functionality you would like
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to use.
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Synopsis
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--------
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.. code-block:: sh
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__TYPE ID --parameter value [--parameter value ...]
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__TYPE --parameter value [--parameter value ...] (for singletons)
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How to use a type
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-----------------
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You can use types from the initial manifest or the type manifest like a
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normal shell command:
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.. code-block:: sh
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# Creates empty file /etc/cdist-configured
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__file /etc/cdist-configured --type file
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# Ensure tree is installed
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__package tree --state installed
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A list of supported types can be found in the `cdist reference <cdist-reference.html>`_ manpage.
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Singleton types
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---------------
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If a type is flagged as a singleton, it may be used only
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once per host. This is useful for types which can be used only once on a
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system. Singleton types do not take an object name as argument.
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Example:
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.. code-block:: sh
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# __issue type manages /etc/issue
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__issue
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# Probably your own type - singletons may use parameters
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__myfancysingleton --colour green
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How to write a new type
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-----------------------
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A type consists of
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- parameter (optional)
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- manifest (optional)
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- singleton (optional)
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- explorer (optional)
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- gencode (optional)
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Types are stored below cdist/conf/type/. Their name should always be prefixed with
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two underscores (__) to prevent collisions with other executables in $PATH.
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To implement a new type, create the directory **cdist/conf/type/__NAME**.
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Defining parameters
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-------------------
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Every type consists of required, optional and boolean parameters, which must
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each be declared in a newline separated file in **parameter/required**,
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**parameter/required_multiple**, **parameter/optional**,
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**parameter/optional_multiple** and **parameter/boolean**.
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Parameters which are allowed multiple times should be listed in
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required_multiple or optional_multiple respectively. All other parameters
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follow the standard unix behaviour "the last given wins".
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If either is missing, the type will have no required, no optional, no boolean
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or no parameters at all.
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Default values for optional parameters can be predefined in
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**parameter/default/<name>**.
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Example:
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.. code-block:: sh
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echo servername >> cdist/conf/type/__nginx_vhost/parameter/required
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echo logdirectory >> cdist/conf/type/__nginx_vhost/parameter/optional
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echo loglevel >> cdist/conf/type/__nginx_vhost/parameter/optional
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mkdir cdist/conf/type/__nginx_vhost/parameter/default
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echo warning > cdist/conf/type/__nginx_vhost/parameter/default/loglevel
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echo server_alias >> cdist/conf/type/__nginx_vhost/parameter/optional_multiple
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echo use_ssl >> cdist/conf/type/__nginx_vhost/parameter/boolean
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Using parameters
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----------------
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The parameters given to a type can be accessed and used in all type scripts
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(e.g manifest, gencode, explorer). Note that boolean parameters are
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represented by file existence. File exists -> True,
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file does not exist -> False
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Example: (e.g. in cdist/conf/type/__nginx_vhost/manifest)
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.. code-block:: sh
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# required parameter
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servername="$(cat "$__object/parameter/servername")"
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# optional parameter
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if [ -f "$__object/parameter/logdirectory" ]; then
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logdirectory="$(cat "$__object/parameter/logdirectory")"
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fi
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# optional parameter with predefined default
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loglevel="$(cat "$__object/parameter/loglevel")"
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# boolean parameter
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if [ -f "$__object/parameter/use_ssl" ]; then
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# file exists -> True
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# do some fancy ssl stuff
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fi
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# parameter with multiple values
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if [ -f "$__object/parameter/server_alias" ]; then
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for alias in $(cat "$__object/parameter/server_alias"); do
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echo $alias > /some/where/usefull
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done
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fi
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Input from stdin
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----------------
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Every type can access what has been written on stdin when it has been called.
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The result is saved into the **stdin** file in the object directory.
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Example use of a type: (e.g. in cdist/conf/type/__archlinux_hostname)
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.. code-block:: sh
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__file /etc/rc.conf --source - << eof
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...
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HOSTNAME="$__target_host"
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...
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eof
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If you have not seen this syntax (<< eof) before, it may help you to read
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about "here documents".
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In the __file type, stdin is used as source for the file, if - is used for source:
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.. code-block:: sh
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if [ -f "$__object/parameter/source" ]; then
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source="$(cat "$__object/parameter/source")"
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if [ "$source" = "-" ]; then
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source="$__object/stdin"
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fi
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....
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Writing the manifest
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--------------------
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In the manifest of a type you can use other types, so your type extends
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their functionality. A good example is the __package type, which in
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a shortened version looks like this:
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.. code-block:: sh
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os="$(cat "$__global/explorer/os")"
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case "$os" in
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archlinux) type="pacman" ;;
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debian|ubuntu) type="apt" ;;
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gentoo) type="emerge" ;;
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*)
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echo "Don't know how to manage packages on: $os" >&2
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exit 1
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;;
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esac
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__package_$type "$@"
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As you can see, the type can reference different environment variables,
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which are documented in `cdist reference <cdist-reference.html>`_.
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Always ensure the manifest is executable, otherwise cdist will not be able
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to execute it. For more information about manifests see `cdist manifest <cdist-manifest.html>`_.
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Singleton - one instance only
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-----------------------------
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If you want to ensure that a type can only be used once per target, you can
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mark it as a singleton: Just create the (empty) file "singleton" in your type
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directory:
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.. code-block:: sh
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touch cdist/conf/type/__NAME/singleton
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This will also change the way your type must be called:
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.. code-block:: sh
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__YOURTYPE --parameter value
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As you can see, the object ID is omitted, because it does not make any sense,
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if your type can be used only once.
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The type explorers
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------------------
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If a type needs to explore specific details, it can provide type specific
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explorers, which will be executed on the target for every created object.
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The explorers are stored under the "explorer" directory below the type.
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It could for instance contain code to check the md5sum of a file on the
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client, like this (shortened version from the type __file):
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.. code-block:: sh
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if [ -f "$__object/parameter/destination" ]; then
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destination="$(cat "$__object/parameter/destination")"
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else
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destination="/$__object_id"
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fi
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if [ -e "$destination" ]; then
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md5sum < "$destination"
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fi
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Writing the gencode script
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--------------------------
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There are two gencode scripts: **gencode-local** and **gencode-remote**.
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The output of gencode-local is executed locally, whereas
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the output of gencode-remote is executed on the target.
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The gencode scripts can make use of the parameters, the global explorers
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and the type specific explorers.
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If the gencode scripts encounters an error, it should print diagnostic
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messages to stderr and exit non-zero. If you need to debug the gencode
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script, you can write to stderr:
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.. code-block:: sh
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# Debug output to stderr
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echo "My fancy debug line" >&2
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# Output to be saved by cdist for execution on the target
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echo "touch /etc/cdist-configured"
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Variable access from the generated scripts
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------------------------------------------
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In the generated scripts, you have access to the following cdist variables
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- __object
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- __object_id
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but only for read operations, means there is no back copy of this
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files after the script execution.
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So when you generate a script with the following content, it will work:
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.. code-block:: sh
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if [ -f "$__object/parameter/name" ]; then
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name="$(cat "$__object/parameter/name")"
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else
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name="$__object_id"
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fi
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Hints for typewriters
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----------------------
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It must be assumed that the target is pretty dumb and thus does not have high
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level tools like ruby installed. If a type requires specific tools to be present
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on the target, there must be another type that provides this tool and the first
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type should create an object of the specific type.
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If your type wants to save temporary data, that may be used by other types
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later on (for instance \__file), you can save them in the subdirectory
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"files" below $__object (but you must create it yourself).
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cdist will not touch this directory.
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If your type contains static files, it's also recommended to place them in
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a folder named "files" within the type (again, because cdist guarantees to
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never ever touch this folder).
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How to include a type into upstream cdist
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-----------------------------------------
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If you think your type may be useful for others, ensure it works with the
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current master branch of cdist and have a look at `cdist hacking <cdist-hacker.html>`_ on
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how to submit it.
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