14. cdist-type(7)¶

Functionality bundled

Nico Schottelius <nico-cdist--@--schottelius.org>

14.1. SYNOPSIS¶

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

14.2. 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.

14.3. HOW TO USE A TYPE¶

You can use types from the initial manifest or the type manifest like a normal shell command:

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

# Ensure tree is installed
__package tree --state installed

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

14.4. SINGLETON TYPES¶

If a type is flagged as a singleton, it may be used only once per host. This is useful for types which can be used only once on a system. Singleton types do not take an object name as argument.

Example:

# __issue type manages /etc/issue
__issue

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

14.5. HOW TO WRITE A NEW TYPE¶

A type consists of

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

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

To implement a new type, create the directory cdist/conf/type/__NAME.

14.6. DEFINING PARAMETERS¶

Every type consists of required, optional and boolean parameters, which must each be declared in a newline separated file in parameter/required, parameter/required_multiple, parameter/optional, parameter/optional_multiple and parameter/boolean. Parameters which are allowed multiple times should be listed in required_multiple or optional_multiple respectively. All other parameters follow the standard unix behaviour “the last given wins”. If either is missing, the type will have no required, no optional, no boolean or no parameters at all.

Default values for optional parameters can be predefined in parameter/default/<name>.

Example:

echo servername >> cdist/conf/type/__nginx_vhost/parameter/required
echo logdirectory >> cdist/conf/type/__nginx_vhost/parameter/optional
echo loglevel >> cdist/conf/type/__nginx_vhost/parameter/optional
mkdir cdist/conf/type/__nginx_vhost/parameter/default
echo warning > cdist/conf/type/__nginx_vhost/parameter/default/loglevel
echo server_alias >> cdist/conf/type/__nginx_vhost/parameter/optional_multiple
echo use_ssl >> cdist/conf/type/__nginx_vhost/parameter/boolean

14.7. USING PARAMETERS¶

The parameters given to a type can be accessed and used in all type scripts (e.g manifest, gencode, explorer). Note that boolean parameters are represented by file existence. File exists -> True, file does not exist -> False

Example: (e.g. in cdist/conf/type/__nginx_vhost/manifest)

# required parameter
servername="$(cat "$__object/parameter/servername")"

# optional parameter
if [ -f "$__object/parameter/logdirectory" ]; then
   logdirectory="$(cat "$__object/parameter/logdirectory")"
fi

# optional parameter with predefined default
loglevel="$(cat "$__object/parameter/loglevel")"

# boolean parameter
if [ -f "$__object/parameter/use_ssl" ]; then
   # file exists -> True
   # do some fancy ssl stuff
fi

# parameter with multiple values
if [ -f "$__object/parameter/server_alias" ]; then
   for alias in $(cat "$__object/parameter/server_alias"); do
      echo $alias > /some/where/usefull
   done
fi

14.8. INPUT FROM STDIN¶

Every type can access what has been written on stdin when it has been called. The result is saved into the stdin file in the object directory.

Example use of a type: (e.g. in cdist/conf/type/__archlinux_hostname)

__file /etc/rc.conf --source - << eof
...
HOSTNAME="$__target_host"
...
eof

If you have not seen this syntax (<< eof) before, it may help you to read about “here documents”.

In the __file type, stdin is used as source for the file, if - is used for source:

if [ -f "$__object/parameter/source" ]; then
    source="$(cat "$__object/parameter/source")"
    if [ "$source" = "-" ]; then
        source="$__object/stdin"
    fi
....

14.9. 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-reference(7).

Always ensure the manifest is executable, otherwise cdist will not be able to execute it. For more information about manifests see cdist-manifest(7).

14.10. SINGLETON - ONE 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:

touch cdist/conf/type/__NAME/singleton

This will also change the way your type must be called:

__YOURTYPE --parameter value

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

14.11. 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 the 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

14.12. 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 scripts can make use of the parameters, the global explorers and the type specific explorers.

If the gencode scripts 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"

14.13. VARIABLE ACCESS FROM THE GENERATED SCRIPTS¶

In the generated scripts, you have access to the following cdist variables

__object
__object_id

but only for read operations, means there is no back copy of this files after the script execution.

So when you generate a script with the following content, it will work:

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

14.14. 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 temporary 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 recommended to place them in a folder named “files” within the type (again, because cdist guarantees to never ever touch this folder).

14.15. 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 have a look at cdist-hacker(7) on how to submit it.