# Master Tops System

In 0.10.4 the external_nodes system was upgraded to allow for modular subsystems to be used to generate the top file data for a highstate run on the master.

The old external_nodes option has been removed. The master tops system provides a pluggable and extendable replacement for it, allowing for multiple different subsystems to provide top file data.

Using the new master_tops option is simple:

    master_tops:
      ext_nodes: cobbler-external-nodes

for `Cobbler` or:

    master_tops:
      reclass:
        inventory_base_uri: /etc/reclass
        classes_uri: roles

for `Reclass`.

    master_tops:
      varstack: /path/to/the/config/file/varstack.yaml

for `Varstack`.

It's also possible to create custom master_tops modules. Simply place them into `salt://_tops` in the Salt fileserver and use the `saltutil.sync_tops` runner to sync them. If this runner function is not available, they can manually be placed into `extmods/tops`, relative to the master cachedir (in most cases the full path will be `/var/cache/salt/master/extmods/tops`).

Custom tops modules are written like any other execution module, see the source for the two modules above for examples of fully functional ones. Below is a bare-bones example:

/etc/salt/master:

    master_tops:
      customtop: True

customtop.py: (custom master_tops module)

    import logging
    import sys

    # Define the module's virtual name
    __virtualname__ = "customtop"

    log = logging.getLogger(__name__)

    def __virtual__():
        return __virtualname__

    def top(**kwargs):
        log.debug("Calling top in customtop")
        return {"base": ["test"]}

salt minion state.show_top should then display something like:

    $ salt minion state.show_top

    minion
        ----------
        base:
          - test

Note

If a master_tops module returns top file data for a given minion, it will be added to the states configured in the top file. It will not replace it altogether. The 2018.3.0 release adds additional functionality allowing a minion to treat master_tops as the single source of truth, irrespective of the top file.