Saltstack: Call runner from minion (jinja conditionals)

2020-03-15T21:05:23Z

---

Contents

• Introduction
• Pre-Requisites
• Preparation
• Execution

---

Introduction

Sometimes a minion may need to execute something which is central to whole system but based on some condition. e.g. Minion may need to update an external common Database whose write access is given only to master. Therefore minion may need to ask salt-master to execute on its behalf. This can be done by

• Minion calling runner on salt-master
• runner executing a custom execution module that provides access to DB

As a custom execution module needs to be executed on salt-master, therefore salt-minion also needs to be installed on salt-master. And configure salt-minion to accept the commands from salt-master. This will be configured as a normal salt-minion. Nothing special needs to be done. Thus salt-master machine would be running both salt-master and salt-minion.

Once above DB operation is done, something else might need to be done. This can be achieved by using jinja in state files.

Pre-Requisites

• salt-master installed and configured on a machine. I used fedora-24 VM.
• salt-minion installed and configured to accept command from salt-master.

Preparation

/etc/salt/master file used.

log_level: debug

peer_run:
  .*:
    - .*

fileserver_backend:
  - roots

file_roots:
  base:
    - /srv/salt

runner_dirs:
  - /srv/salt/_runners

/etc/salt/minion file used.

master: salt

Note: In /etc/salt/master file, log_level is set to debug. Normally this will be info. Also take a note of peer_run config. This is must. At the moment this is very open and you may like to narrow it down.

my_module.py will be our execution module.

mkdir /srv/salt/_modules
touch /srv/salt/_modules/my_module.py
mkdir /srv/salt/_runners
touch /srv/salt/_runners/my_runner.py

Contents of /srv/salt/_modules/my_module.py are as follows.

#! /usr/bin/env python

# Below virtual name can be any string.
__virtualname__ = 'my_module'

def __virtual__():
    return __virtualname__

def my_module_function(arg1, arg2):
    modified_arg1 = '%s_%s' % (arg1, 'modified')
    modified_arg2 = '%s_%s' % (arg2, 'modified')
    return True

Contents of /srv/salt/_runners/my_runner.py are as follows.

#! /usr/bin/env python
import salt.client
import salt.loader
import salt.config

def my_runner_function(arg1, arg2):
    __opts__ = salt.config.minion_config('/etc/salt/master')
    mods = salt.loader.minion_mods(__opts__)
    ret = mods['my_module.my_module_function'](arg1, arg2)
    return ret

Above runner can be called from command line as follows:

root@salt-master# salt-run my_runner.my_runner_function 'a_string' 'b_string'
True
[INFO    ] Runner completed: 20170109200157859211

Now we will ask minion to execute runner on master.

Create a state file /srv/salt/jinja_state_file_calling_runner_on_master.sls as following:

{% set some_changes = salt['publish.runner']('my_runner.my_runner_function', ['argument1', 'argument2']) %}

{% if some_changes == True %}
install tcpdump:
  pkg.installed:
    - name: tcpdump
{% else %}
install git:
  pkg.installed:
    - name: git
{% endif %}

Note1: In above state file, if the execution of execution module my_module is True then tcpdump will be installed otherwise git will be installed.

Execution

Run following command to sync all modules with all minions.

root@salt-master# salt '*' saltutil.sync_all
fedora2.vagrant.box:
    ----------
    beacons:
    engines:
    grains:
    log_handlers:
    modules:
        - modules.custom_module
        - modules.my_module
    output:
    proxymodules:
    renderers:
    returners:
    sdb:
    states:
    utils:
fedora.vagrant.box:
    ----------
    beacons:
    engines:
    grains:
    log_handlers:
    modules:
        - modules.custom_module
        - modules.my_module
    output:
    proxymodules:
    renderers:
    returners:
    sdb:
    states:
    utils:

Now execute above state file on remote minion by running following command.

root@salt-master# salt 'fedora2.vagrant.box' state.sls jinja_state_file_calling_runner_on_master
fedora2.vagrant.box:
----------
          ID: install tcpdump
    Function: pkg.installed
        Name: tcpdump
      Result: True
     Comment: Package tcpdump is already installed
     Started: 20:05:03.065341
    Duration: 420.049 ms
     Changes:

Summary for fedora2.vagrant.box
------------
Succeeded: 1
Failed:    0
------------
Total states run:     1
Total run time: 420.049 ms