.. _requisites: =========================================== Requisites and Other Global State Arguments =========================================== Requisites ========== The Salt requisite system is used to create relationships between states. The core idea being that, when one state is dependent somehow on another, that inter-dependency can be easily defined. Requisites come in two types: Direct requisites (such as ``require``), and requisite_ins (such as ``require_in``). The relationships are directional: a direct requisite requires something from another state. However, a requisite_in inserts a requisite into the targeted state pointing to the targeting state. The following example demonstrates a direct requisite: .. code-block:: yaml vim: pkg.installed: [] /etc/vimrc: file.managed: - source: salt://edit/vimrc - require: - pkg: vim In the example above, the file ``/etc/vimrc`` depends on the vim package. Requisite_in statements are the opposite. Instead of saying "I depend on something", requisite_ins say "Someone depends on me": .. code-block:: yaml vim: pkg.installed: - require_in: - file: /etc/vimrc /etc/vimrc: file.managed: - source: salt://edit/vimrc So here, with a requisite_in, the same thing is accomplished as in the first example, but the other way around. The vim package is saying "/etc/vimrc depends on me". This will result in a ``require`` being inserted into the ``/etc/vimrc`` state which targets the ``vim`` state. In the end, a single dependency map is created and everything is executed in a finite and predictable order. .. note:: Requisite matching Requisites match on both the ID Declaration and the ``name`` parameter. This means that, in the example above, the ``require_in`` requisite would also have been matched if the ``/etc/vimrc`` state was written as follows: .. code-block:: yaml vimrc: file.managed: - name: /etc/vimrc - source: salt://edit/vimrc Direct Requisite and Requisite_in types --------------------------------------- There are six direct requisite statements that can be used in Salt: ``require``, ``watch``, ``prereq``, ``use``, ``onchanges``, and ``onfail``. Each direct requisite also has a corresponding requisite_in: ``require_in``, ``watch_in``, ``prereq_in``, ``use_in``, ``onchanges_in``, and ``onfail_in``. All of the requisites define specific relationships and always work with the dependency logic defined above. .. _requisites-require: require ~~~~~~~ The use of ``require`` demands that the dependent state executes before the depending state. The state containing the ``require`` requisite is defined as the depending state. The state specified in the ``require`` statement is defined as the dependent state. If the dependent state's execution succeeds, the depending state will then execute. If the dependent state's execution fails, the depending state will not execute. In the first example above, the file ``/etc/vimrc`` will only execute after the vim package is installed successfully. Require an entire sls file ~~~~~~~~~~~~~~~~~~~~~~~~~~ As of Salt 0.16.0, it is possible to require an entire sls file. Do this first by including the sls file and then setting a state to ``require`` the included sls file: .. code-block:: yaml include: - foo bar: pkg.installed: - require: - sls: foo .. _requisites-watch: watch ~~~~~ ``watch`` statements are used to add additional behavior when there are changes in other states. .. note:: If a state should only execute when another state has changes, and otherwise do nothing, the new ``onchanges`` requisite should be used instead of ``watch``. ``watch`` is designed to add *additional* behavior when there are changes, but otherwise execute normally. The state containing the ``watch`` requisite is defined as the watching state. The state specified in the ``watch`` statement is defined as the watched state. When the watched state executes, it will return a dictionary containing a key named "changes". Here are two examples of state return dictionaries, shown in json for clarity: .. code-block:: json "local": { "file_|-/tmp/foo_|-/tmp/foo_|-directory": { "comment": "Directory /tmp/foo updated", "__run_num__": 0, "changes": { "user": "bar" }, "name": "/tmp/foo", "result": true } } "local": { "pkgrepo_|-salt-minion_|-salt-minion_|-managed": { "comment": "Package repo 'salt-minion' already configured", "__run_num__": 0, "changes": {}, "name": "salt-minion", "result": true } } If the "result" of the watched state is ``True``, the watching state *will execute normally*. This part of ``watch`` mirrors the functionality of the ``require`` requisite. If the "result" of the watched state is ``False``, the watching state will never run, nor will the watching state's ``mod_watch`` function execute. However, if the "result" of the watched state is ``True``, and the "changes" key contains a populated dictionary (changes occurred in the watched state), then the ``watch`` requisite can add additional behavior. This additional behavior is defined by the ``mod_watch`` function within the watching state module. If the ``mod_watch`` function exists in the watching state module, it will be called *in addition to* the normal watching state. The return data from the ``mod_watch`` function is what will be returned to the master in this case; the return data from the main watching function is discarded. If the "changes" key contains an empty dictionary, the ``watch`` requisite acts exactly like the ``require`` requisite (the watching state will execute if "result" is ``True``, and fail if "result" is ``False`` in the watched state). .. note:: Not all state modules contain ``mod_watch``. If ``mod_watch`` is absent from the watching state module, the ``watch`` requisite behaves exactly like a ``require`` requisite. A good example of using ``watch`` is with a :mod:`service.running ` state. When a service watches a state, then the service is reloaded/restarted when the watched state changes, in addition to Salt ensuring that the service is running. .. code-block:: yaml ntpd: service.running: - watch: - file: /etc/ntp.conf file.managed: - name: /etc/ntp.conf - source: salt://ntp/files/ntp.conf .. _requisites-prereq: prereq ~~~~~~ .. versionadded:: 0.16.0 ``prereq`` allows for actions to be taken based on the expected results of a state that has not yet been executed. The state containing the ``prereq`` requisite is defined as the pre-requiring state. The state specified in the ``prereq`` statement is defined as the pre-required state. When a ``prereq`` requisite is evaluated, the pre-required state reports if it expects to have any changes. It does this by running the pre-required single state as a test-run by enabling ``test=True``. This test-run will return a dictionary containing a key named "changes". (See the ``watch`` section above for examples of "changes" dictionaries.) If the "changes" key contains a populated dictionary, it means that the pre-required state expects changes to occur when the state is actually executed, as opposed to the test-run. The pre-requiring state will now actually run. If the pre-requiring state executes successfully, the pre-required state will then execute. If the pre-requiring state fails, the pre-required state will not execute. If the "changes" key contains an empty dictionary, this means that changes are not expected by the pre-required state. Neither the pre-required state nor the pre-requiring state will run. The best way to define how ``prereq`` operates is displayed in the following practical example: When a service should be shut down because underlying code is going to change, the service should be off-line while the update occurs. In this example, ``graceful-down`` is the pre-requiring state and ``site-code`` is the pre-required state. .. code-block:: yaml graceful-down: cmd.run: - name: service apache graceful - prereq: - file: site-code site-code: file.recurse: - name: /opt/site_code - source: salt://site/code In this case the apache server will only be shutdown if the site-code state expects to deploy fresh code via the file.recurse call. The site-code deployment will only be executed if the graceful-down run completes successfully. onfail ~~~~~~ .. versionadded:: 2014.7.0 The ``onfail`` requisite allows for reactions to happen strictly as a response to the failure of another state. This can be used in a number of ways, such as executing a second attempt to set up a service or begin to execute a separate thread of states because of a failure. The ``onfail`` requisite is applied in the same way as ``require`` as ``watch``: .. code-block:: yaml primary_mount: mount.mounted: - name: /mnt/share - device: 10.0.0.45:/share - fstype: nfs backup_mount: mount.mounted: - name: /mnt/share - device: 192.168.40.34:/share - fstype: nfs - onfail: - mount: primary_mount onchanges ~~~~~~~~~ .. versionadded:: 2014.7.0 The ``onchanges`` requisite makes a state only apply if the required states generate changes, and if the watched state's "result" is ``True``. This can be a useful way to execute a post hook after changing aspects of a system. use ~~~ The ``use`` requisite is used to inherit the arguments passed in another id declaration. This is useful when many files need to have the same defaults. .. code-block:: yaml /etc/foo.conf: file.managed: - source: salt://foo.conf - template: jinja - mkdirs: True - user: apache - group: apache - mode: 755 /etc/bar.conf file.managed: - source: salt://bar.conf - use: - file: /etc/foo.conf The ``use`` statement was developed primarily for the networking states but can be used on any states in Salt. This makes sense for the networking state because it can define a long list of options that need to be applied to multiple network interfaces. The ``use`` statement does not inherit the requisites arguments of the targeted state. This means also a chain of ``use`` requisites would not inherit inherited options. .. _requisites-require-in: .. _requisites-watch-in: The _in versions of requisites ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ All of the requisites also have corresponding requisite_in versions, which do the reverse of their normal counterparts. The examples below all use ``require_in`` as the example, but note that all of the ``_in`` requisites work the same way: They result in a normal requisite in the targeted state, which targets the state which has defines the requisite_in. Thus, a ``require_in`` causes the target state to ``require`` the targeting state. Similarly, a ``watch_in`` causes the target state to ``watch`` the targeting state. This pattern continues for the rest of the requisites. If a state declaration needs to be required by another state declaration then ``require_in`` can accommodate it. Therefore, these two sls files would be the same in the end: Using ``require`` .. code-block:: yaml httpd: pkg.installed: [] service.running: - require: - pkg: httpd Using ``require_in`` .. code-block:: yaml httpd: pkg.installed: - require_in: - service: httpd service.running: [] The ``require_in`` statement is particularly useful when assigning a require in a separate sls file. For instance it may be common for httpd to require components used to set up PHP or mod_python, but the HTTP state does not need to be aware of the additional components that require it when it is set up: http.sls .. code-block:: yaml httpd: pkg.installed: [] service.running: - require: - pkg: httpd php.sls .. code-block:: yaml include: - http php: pkg.installed: - require_in: - service: httpd mod_python.sls .. code-block:: yaml include: - http mod_python: pkg.installed: - require_in: - service: httpd Now the httpd server will only start if php or mod_python are first verified to be installed. Thus allowing for a requisite to be defined "after the fact". Altering States =============== The state altering system is used to make sure that states are evaluated exactly as the user expects. It can be used to double check that a state preformed exactly how it was expected to, or to make 100% sure that a state only runs under certain conditions. The use of unless or onlyif options help make states even more stateful. The check_cmds option helps ensure that the result of a state is evaluated correctly. Unless ------ .. versionadded:: 2014.7.0 The ``unless`` requisite specifies that a state should only run when any of the specified commands return ``False``. The ``unless`` requisite operates as NOR and is useful in giving more granular control over when a state should execute. .. code-block:: yaml vim: pkg.installed: - unless: - rpm -q vim-enhanced - ls /usr/bin/vim In the example above, the state will only run if either the vim-enhanced package is not installed (returns ``False``) or if /usr/bin/vim does not exist (returns ``False``). The state will run if both commands return ``False``. However, the state will not run if both commands return ``True``. Onlyif ------ .. versionadded:: 2014.7.0 ``onlyif`` is the opposite of ``unless``. If all of the commands in ``onlyif`` return ``True``, then the state is run. If any of the specified commands return ``False``, the state will not run. .. code-block:: yaml stop-volume: module.run: - name: glusterfs.stop_volume - m_name: work - onlyif: - gluster volume status work - order: 1 remove-volume: module.run: - name: glusterfs.delete - m_name: work - onlyif: - gluster volume info work - watch: - cmd: stop-volume The above example ensures that the stop_volume and delete modules only run if the gluster commands return a 0 ret value. check_cmd --------- .. versionadded:: 2014.7.0 Check Command is used for determining that a state did or did not run as expected. .. code-block:: yaml comment-repo: file.replace: - path: /etc/yum.repos.d/fedora.repo - pattern: ^enabled=0 - repl: enabled=1 - check_cmd: - grep 'enabled=0' /etc/yum.repos.d/fedora.repo && return 1 || return 0 This will attempt to do a replace on all enabled=0 in the .repo file, and replace them with enabled=1. The check_cmd is just a bash command. It will do a grep for enabled=0 in the file, and if it finds any, it will return a 0, which will prompt the && portion of the command to return a 1, causing check_cmd to set the state as failed. If it returns a 1, meaning it didn't find any 'enabled=0' it will hit the || portion of the command, returning a 0, and declaring the function succeeded. Overriding Checks ----------------- There are two commands used for the above checks. `mod_run_check` is used to check for onlyif and unless. If the goal is to override the global check for these to variables, include a mod_run_check in the salt/states/ file. `mod_run_check_cmd` is used to check for the check_cmd options. To override this one, include a mod_run_check_cmd in the states file for the state.