Salt provides several special "dunder" dictionaries as a convenience for Salt
development. These include
others. This document will describe each dictionary and detail where they exist
and what information and/or functionality they provide.
__opts__ dictionary contains all of the options passed in the
configuration file for the master or minion.
In many places in salt, instead of pulling raw data from the __opts__ dict, configuration data should be pulled from the salt get functions such as config.get, aka - __salt__['config.get']('foo:bar') The get functions also allow for dict traversal via the : delimiter. Consider using get functions whenever using __opts__ or __pillar__ and __grains__ (when using grains for configuration data)
The configuration file data made available in the
__opts__ dictionary is the
configuration data relative to the running daemon. If the modules are loaded and
executed by the master, then the master configuration data is available, if the
modules are executed by the minion, then the minion configuration is
available. Any additional information passed into the respective configuration
files is made available
__salt__ contains the execution module functions. This allows for all
functions to be called as they have been set up by the salt loader.
__salt__['cmd.run']('fdisk -l') __salt__['network.ip_addrs']()
__grains__ dictionary contains the grains data generated by the minion
that is currently being worked with. In execution modules, state modules and
returners this is the grains of the minion running the calls, when generating
the external pillar the
__grains__ is the grains data from the minion that
the pillar is being generated for.
__pillar__ dictionary contains the pillar for the respective minion.
__context__ exists in state modules and execution modules.
During a state run the
__context__ dictionary persists across all states
that are run and then is destroyed when the state ends.
When running an execution module
__context__ persists across all module
executions until the modules are refreshed; such as when
state.highstate are executed.
A great place to see how to use
__context__ is in the cp.py module in
salt/modules/cp.py. The fileclient authenticates with the master when it is
instantiated and then is used to copy files to the minion. Rather than create a
new fileclient for each file that is to be copied down, one instance of the
fileclient is instantiated in the
__context__ dictionary and is reused for
each file. Here is an example from salt/modules/cp.py:
if not 'cp.fileclient' in __context__: __context__['cp.fileclient'] = salt.fileclient.get_file_client(__opts__)
Because __context__ may or may not have been destroyed, always be sure to check for the existence of the key in __context__ and generate the key before using it.