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278 lines
9.5 KiB
ReStructuredText
278 lines
9.5 KiB
ReStructuredText
==============
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Reactor System
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==============
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Salt version 0.11.0 introduced the reactor system. The premise behind the
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reactor system is that with Salt's events and the ability to execute commands,
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a logic engine could be put in place to allow events to trigger actions, or
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more accurately, reactions.
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This system binds sls files to event tags on the master. These sls files then
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define reactions. This means that the reactor system has two parts. First, the
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reactor option needs to be set in the master configuration file. The reactor
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option allows for event tags to be associated with sls reaction files. Second,
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these reaction files use highdata (like the state system) to define reactions
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to be executed.
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Event System
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============
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A basic understanding of the event system is required to understand reactors.
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The event system is a local ZeroMQ PUB interface which fires salt events. This
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event bus is an open system used for sending information notifying Salt and
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other systems about operations.
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The event system fires events with a very specific criteria. Every event has a
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:strong:`tag`. Event tags allow for fast top level filtering of events. In
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addition to the tag, each event has a data structure. This data structure is a
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dict, which contains information about the event.
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Mapping Events to Reactor SLS Files
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===================================
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Reactor SLS files and event tags are associated in the master config file.
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By default this is /etc/salt/master, or /etc/salt/master.d/reactor.conf.
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In the master config section 'reactor:' is a list of event tags to be matched
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and each event tag has a list of reactor SLS files to be run.
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.. code-block:: yaml
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reactor: # Master config section "reactor"
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- 'salt/minion/*/start': # Match tag "salt/minion/*/start"
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- /srv/reactor/start.sls # Things to do when a minion starts
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- /srv/reactor/monitor.sls # Other things to do
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- 'salt/cloud/*/destroyed': # Globs can be used to matching tags
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- /srv/reactor/decommision.sls # Things to do when a server is removed
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Reactor sls files are similar to state and pillar sls files. They are
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by default yaml + Jinja templates and are passed familar context variables.
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They differ because of the addtion of the ``tag`` and ``data`` variables.
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- The ``tag`` variable is just the tag in the fired event.
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- The ``data`` variable is the event's data dict.
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Here is a simple reactor sls:
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.. code-block:: yaml
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{% if data['id'] == 'mysql1' %}
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highstate_run:
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cmd.state.highstate:
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- tgt: mysql1
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{% endif %}
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This simple reactor file uses Jinja to further refine the reaction to be made.
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If the ``id`` in the event data is ``mysql1`` (in other words, if the name of
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the minion is ``mysql1``) then the following reaction is defined. The same
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data structure and compiler used for the state system is used for the reactor
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system. The only difference is that the data is matched up to the salt command
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API and the runner system. In this example, a command is published to the
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``mysql1`` minion with a function of ``state.highstate``. Similarly, a runner
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can be called:
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.. code-block:: yaml
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{% if data['data']['overstate'] == 'refresh' %}
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overstate_run:
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runner.state.over
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{% endif %}
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This example will execute the state.overstate runner and initiate an overstate
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execution.
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Fire an event
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=============
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To fire an event from a minion call ``event.fire_master``
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.. code-block:: bash
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salt-call event.fire_master '{"overstate": "refresh"}' 'foo'
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After this is called, any reactor sls files matching event tag ``foo`` will
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execute with ``{{ data['data']['overstate'] }}`` equal to ``'refresh'``.
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See :py:mod:`salt.modules.event` for more information.
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Knowing what event is being fired
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=================================
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Knowing exactly which event is being fired and what data is has for use in the
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sls files can be challenging. The easiest way to see exactly what's going on is
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to use the :strong:`eventlisten.py` script. This script is not part of packages
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but is part of the source.
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If the master process is using the default socket, no additional options will be
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required. Otherwise, you will need to specify the socket location.
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Example usage:
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wget https://raw.github.com/saltstack/salt/develop/tests/eventlisten.py
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python eventlisten.py
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OR: python eventlisten.py --sock-dir /path/to/var/run/salt
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Example output:
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Event fired at Fri Dec 20 10:43:00 2013
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*************************
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Tag: salt/auth
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Data:
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{'_stamp': '2013-12-20_10:47:54.584699',
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'act': 'accept',
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'id': 'fuzzer.domain.tld',
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'pub': '-----BEGIN PUBLIC KEY-----\nMIICIDANBgk+TRIMMED+EMZ8CAQE=\n-----END PUBLIC KEY-----\n',
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'result': True}
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Event fired at Fri Dec 20 10:43:01 2013
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*************************
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Tag: salt/minion/fuzzer.domain.tld/start
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Data:
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{'_stamp': '2013-12-20_10:43:01.638387',
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'cmd': '_minion_event',
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'data': 'Minion fuzzer.domain.tld started at Fri Dec 20 10:43:01 2013',
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'id': 'fuzzer.domain.tld',
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'pretag': None,
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'tag': 'salt/minion/fuzzer.domain.tld/start'}
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Understanding the Structure of Reactor Formulas
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===============================================
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While the reactor system uses the same data structure as the state system, this
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data does not translate the same way to operations. In state files formula
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information is mapped to the state functions, but in the reactor system
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information is mapped to a number of available subsystems on the master. These
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systems are the :strong:`LocalClient` and the :strong:`Runners`. The
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:strong:`state declaration` field takes a reference to the function to call in
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each interface. So to trigger a salt-run call the :strong:`state declaration`
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field will start with :strong:`runner`, followed by the runner function to
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call. This means that a call to what would be on the command line
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:strong:`salt-run manage.up` will be :strong:`runner.manage.up`. An example of
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this in a reactor formula would look like this:
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.. code-block:: yaml
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manage_up:
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runner.manage.up
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If the runner takes arguments then they can be specified as well:
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.. code-block:: yaml
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overstate_dev_env:
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runner.state.over:
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- env: dev
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Executing remote commands maps to the :strong:`LocalClient` interface which is
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used by the :strong:`salt` command. This interface more specifically maps to
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the :strong:`cmd_async` method inside of the :strong:`LocalClient` class. This
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means that the arguments passed are being passed to the :strong:`cmd_async`
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method, not the remote method. A field starts with :strong:`cmd` to use the
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:strong:`LocalClient` subsystem. The result is, to execute a remote command,
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a reactor fomular would look like this:
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.. code-block:: yaml
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clean_tmp:
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cmd.cmd.run:
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- tgt: '*'
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- arg:
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- rm -rf /tmp/*
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The ``arg`` option takes a list of arguments as they would be presented on the
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command line, so the above declaration is the same as running this salt
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command:
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.. code-block:: bash
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salt '*' cmd.run 'rm -rf /tmp/*'
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Use the ``expr_form`` argument to specify a matcher:
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.. code-block:: yaml
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clean_tmp:
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cmd.cmd.run:
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- tgt: 'os:Ubuntu'
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- expr_form: grain
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- arg:
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- rm -rf /tmp/*
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clean_tmp:
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cmd.cmd.run:
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- tgt: 'G@roles:hbase_master'
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- expr_form: compound
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- arg:
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- rm -rf /tmp/*
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An interesting trick to pass data from the Reactor script to
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``state.highstate`` or ``state.sls`` is to pass it as inline Pillar data since
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both functions take a keyword argument named ``pillar``.
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The following example uses Salt's Reactor to listen for the event that is fired
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when the key for a new minion is accepted on the master using ``salt-key``.
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:file:`/etc/salt/master.d/reactor.conf`:
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.. code-block:: yaml
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reactor:
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- 'salt/key':
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- /srv/salt/haproxy/react_new_minion.sls
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The Reactor then fires a ``state.sls`` command targeted to the HAProxy servers
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and passes the ID of the new minion from the event to the state file via inline
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Pillar.
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Note, the Pillar data will need to be passed as a string since that is how it
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is passed at the CLI. That string will be parsed as YAML on the minion (same as
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how it works at the CLI).
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:file:`/srv/salt/haproxy/react_new_minion.sls`:
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.. code-block:: yaml
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{% if data['act'] == 'accept' and data['id'].startswith('web') %}
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add_new_minion_to_pool:
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cmd.state.sls:
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- tgt: 'haproxy*'
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- arg:
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- haproxy.refresh_pool
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- 'pillar={new_minion: {{ data['id'] }}}'
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{% endif %}
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The above command is equivalent to the following command at the CLI:
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.. code-block:: bash
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salt 'haproxy*' state.sls haproxy.refresh_pool 'pillar={new_minion: minionid}'
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Finally, that data is available in the state file using the normal Pillar
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lookup syntax. The following example is grabbing web server names and IP
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addresses from :ref:`Salt Mine <salt-mine>`. If this state is invoked from the
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Reactor then the custom Pillar value from above will be available and the new
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minion will be added to the pool but with the ``disabled`` flag so that HAProxy
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won't yet direct traffic to it.
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:file:`/srv/salt/haproxy/refresh_pool.sls`:
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.. code-block:: yaml
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{% set new_minion = salt['pillar.get']('new_minion') %}
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listen web *:80
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balance source
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{% for server,ip in salt['mine.get']('web*', 'network.interfaces', ['eth0']).items() %}
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{% if server == new_minion %}
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server {{ server }} {{ ip }}:80 disabled
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{% else %}
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server {{ server }} {{ ip }}:80 check
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{% endif %}
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{% endfor %}
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