State Modules

### Navigation

- index
- modules |
- next |
- previous |
- « SaltStack.org |
- Documentation home

# State Modules

State Modules are the components that map to actual enforcement and management of Salt states.

## States are - Easy to Write!

State Modules should be easy to write and straightforward. The information passed to the SLS data structures will map directly to the states modules.

Mapping the information from the SLS data is simple, this example should illustrate:

    /etc/salt/master: # maps to "name"
      file: # maps to State module filename eg https://github.com/saltstack/salt/blob/develop/salt/states/file.py
        - managed # maps to the managed function in the file State module
        - user: root # one of many options passed to the manage function
        - group: root
        - mode: 644
        - source: salt://salt/master

Therefore this SLS data can be directly linked to a module, function and arguments passed to that function.

This does issue the burden, that function names, state names and function arguments should be very human readable inside state modules, since they directly define the user interface.

## Using Custom State Modules

Place your custom state modules inside a `_states` directory within the `file_roots` specified by the master config file. These custom state modules can then be distributed in a number of ways. Custom state modules are distributed when state.highstate is run, or via the saltutil.sync_states function.

## Cross Calling Modules

As with Execution Modules, State Modules can also make use of the `__salt__` and `__grains__` data.

It is important to note that the real work of state management should not be done in the state module unless it is needed. A good example is the pkg state module. This module does not do any package management work, it just calls the pkg execution module. This makes the pkg state module completely generic, which is why there is only one pkg state module and many backend pkg execution modules.

On the other hand some modules will require that the logic be placed in the state module, a good example of this is the file module. But in the vast majority of cases this is not the best approach, and writing specific execution modules to do the backend work will be the optimal solution.

## Return Data

A State Module must return a dict containing the following keys/values:

- name: The same value passed to the state as "name".
- changes: A dict describing the changes made. Each thing changed should be a key, with its value being another dict with keys called "old" and "new" containing the old/new values. For example, the pkg state's changes dict has one key for each package changed, with the "old" and "new" keys in its sub-dict containing the old and new versions of the package.
- result: A boolean value. True if the action was successful, otherwise False.
- comment: A string containing a summary of the result.

## Test State

All states should check for and support `test` being passed in the options. This will return data about what changes would occur if the state were actually run. An example of such a check could look like this:

    # Return comment of changes if test.
    if __opts__['test']:
        ret['result'] = None
        ret['comment'] = 'State Foo will execute with param {0}'.format(bar)
        return ret

Make sure to test and return before performing any real actions on the minion.

## Watcher Function

If the state being written should support the watch requisite then a watcher function needs to be declared. The watcher function is called whenever the watch requisite is invoked and should be generic to the behavior of the state itself.

The watcher function should accept all of the options that the normal state functions accept (as they will be passed into the watcher function).

A watcher function typically is used to execute state specific reactive behavior, for instance, the watcher for the service module restarts the named service and makes it useful for the watcher to make the service react to changes in the environment.

The watcher function also needs to return the same data that a normal state function returns.

## Mod_init Interface

Some states need to execute something only once to ensure that an environment has been set up, or certain conditions global to the state behavior can be predefined. This is the realm of the mod_init interface.

A state module can have a function called mod_init which executes when the first state of this type is called. This interface was created primarily to improve the pkg state. When packages are installed the package metadata needs to be refreshed, but refreshing the package metadata every time a package is installed is wasteful. The mod_init function for the pkg state sets a flag down so that the first, and only the first, package installation attempt will refresh the package database (the package database can of course be manually called to refresh via the `refresh` option in the pkg state).

The mod_init function must accept the Low State Data for the given executing state as an argument. The low state data is a dict and can be seen by executing the state.show_lowstate function. Then the mod_init function must return a bool. If the return value is True, then the mod_init function will not be executed again, meaning that the needed behavior has been set up. Otherwise, if the mod_init function returns False, then the function will be called the next time.

A good example of the mod_init function is found in the pkg state module:

    def mod_init(low):
        '''
        Refresh the package database here so that it only needs to happen once
        '''
        if low['fun'] == 'installed' or low['fun'] == 'latest':
            rtag = __gen_rtag()
            if not os.path.exists(rtag):
                open(rtag, 'w+').write('')
            return True
        else:
            return False

The mod_init function in the pkg state accepts the low state data as `low` and then checks to see if the function being called is going to install packages, if the function is not going to install packages then there is no need to refresh the package database. Therefore if the package database is prepared to refresh, then return True and the mod_init will not be called the next time a pkg state is evaluated, otherwise return False and the mod_init will be called next time a pkg state is evaluated.

## Comments

comments powered by Disqus

### Navigation

- index
- modules |
- next |
- previous |
- « SaltStack.org |
- Documentation home