The Top File

Introduction

Most infrastructures are made up of groups of machines, each machine in the group performing a role similar to others. Those groups of machines work in concert with each other to create an application stack.

To effectively manage those groups of machines, an administrator needs to be able to create roles for those groups. For example, a group of machines that serve front-end web traffic might have roles which indicate that those machines should all have the Apache webserver package installed and that the Apache service should always be running.

In Salt, the file which contains a mapping between groups of machines on a network and the configuration roles that should be applied to them is called a top file.

Top files are named top.sls by default and they are so-named because they always exist in the "top" of a directory hierarchy that contains state files. That directory hierarchy is called a state tree.

A Basic Example

Top files have three components:

  • Environment: A state tree directory containing a set of state files to configure systems.
  • Target: A grouping of machines which will have a set of states applied to them.
  • State files: A list of state files to apply to a target. Each state file describes one or more states to be configured and enforced on the targeted machines.

The relationship between these three components is nested as follows:

  • Environments contain targets
  • Targets contain states

Putting these concepts together, we can describe a scenario in which all minions with an ID that begins with web have an apache state applied to them:

base:          # Apply SLS files from the directory root for the 'base' environment
  'web*':      # All minions with a minion_id that begins with 'web'
    - apache   # Apply the state file named 'apache.sls'

Environments

Environments are directory hierarchies which contain a top files and a set of state files.

Environments can be used in many ways, however there is no requirement that they be used at all. In fact, the most common way to deploy Salt is with a single environment, called base. It is recommended that users only create multiple environments if they have a use case which specifically calls for multiple versions of state trees.

Getting Started with Top Files

Each environment is defined inside a salt master configuration variable called, file_roots .

In the most common single-environment setup, only the base environment is defined in file_roots along with only one directory path for the state tree.

file_roots:
  base:
    - /srv/salt

In the above example, the top file will only have a single environment to pull from.

Next is a simple single-environment top file placed in /srv/salt/top.sls, illustrating that for the environment called base, all minions will have the state files named core.sls and edit.sls applied to them.

base:
  '*':
    - core
    - edit

Assuming the file_roots configuration from above, Salt will look in the /srv/salt directory for core.sls and edit.sls.

Multiple Environments

In some cases, teams may wish to create versioned state trees which can be used to test Salt configurations in isolated sets of systems such as a staging environment before deploying states into production.

For this case, multiple environments can be used to accomplish this task.

To create multiple environments, the file_roots option can be expanded:

file_roots:
  dev:
    - /srv/salt/dev
  qa:
    - /srv/salt/qa
  prod:
    - /srv/salt/prod

In the above, we declare three environments: dev, qa and prod. Each environment has a single directory assigned to it.

Our top file references the environments:

dev:
  'webserver*':
    - webserver
  'db*':
    - db
qa:
  'webserver*':
    - webserver
  'db*':
    - db
prod:
  'webserver*':
    - webserver
  'db*':
    - db

As seen above, the top file now declares the three environments and for each, targets are defined to map globs of minion IDs to state files. For example, all minions which have an ID beginning with the string webserver will have the webserver state from the requested environment assigned to it.

In this manner, a proposed change to a state could first be made in a state file in /srv/salt/dev and then be applied to development webservers before moving the state into QA by copying the state file into /srv/salt/qa.

Choosing an Environment to Target

The top file is used to assign a minion to an environment unless overridden using the methods described below. The environment in the top file must match valid fileserver environment (a.k.a. saltenv) in order for any states to be applied to that minion. When using the default fileserver backend, environments are defined in file_roots.

The states that will be applied to a minion in a given environment can be viewed using the state.show_top function.

Minions may be pinned to a particular environment by setting the environment value in the minion configuration file. In doing so, a minion will only request files from the environment to which it is assigned.

The environment may also be dynamically selected at runtime by passing it to the salt, salt-call or salt-ssh command. This is most commonly done with functions in the state module by using the saltenv argument. For example, to run a highstate on all minions, using only the top file and SLS files in the prod environment, run: salt '*' state.highstate saltenv=prod.

Note

Not all functions accept saltenv as an argument, see the documentation for an individual function documentation to verify.

Shorthand

If you assign only one SLS to a system, as in this example, a shorthand is also available:

base:
  '*': global
dev:
  'webserver*': webserver
  'db*':        db
qa:
  'webserver*': webserver
  'db*':        db
prod:
  'webserver*': webserver
  'db*':        db

Advanced Minion Targeting

In addition to globs, minions can be specified in top files a few other ways. Some common ones are compound matches and node groups.

Below is a slightly more complex top file example, showing the different types of matches you can perform:

# All files will be taken from the file path specified in the base
# environment in the ``file_roots`` configuration value.

base:
    # All minions get the following three state files applied

    '*':
        - ldap-client
        - networking
        - salt.minion

    # All minions which have an ID that begins with the phrase
    # 'salt-master' will have an SLS file applied that is named
    # 'master.sls' and is in the 'salt' directory, underneath
    # the root specified in the ``base`` environment in the
    # configuration value for ``file_roots``.

    'salt-master*':
        - salt.master

    # Minions that have an ID matching the following regular
    # expression will have the state file called 'web.sls' in the
    # nagios/mon directory applied. Additionally, minions matching
    # the regular expression will also have the 'server.sls' file
    # in the apache/ directory applied.

    # NOTE!
    #
    # Take note of the 'match' directive here, which tells Salt
    # to treat the target string as a regex to be matched!

    '^(memcache|web).(qa|prod).loc$':
        - match: pcre
        - nagios.mon.web
        - apache.server

    # Minions that have a grain set indicating that they are running
    # the Ubuntu operating system will have the state file called
    # 'ubuntu.sls' in the 'repos' directory applied.
    #
    # Again take note of the 'match' directive here which tells
    # Salt to match against a grain instead of a minion ID.

    'os:Ubuntu':
        - match: grain
        - repos.ubuntu

    # Minions that are either RedHat or CentOS should have the 'epel.sls'
    # state applied, from the 'repos/' directory.

    'os:(RedHat|CentOS)':
        - match: grain_pcre
        - repos.epel

    # The three minions with the IDs of 'foo', 'bar' and 'baz' should
    # have 'database.sls' applied.

    'foo,bar,baz':
        - match: list
        - database

    # Any minion for which the pillar key 'somekey' is set and has a value
    # of that key matching 'abc' will have the 'xyz.sls' state applied.

    'somekey:abc':
        - match: pillar
        - xyz

    # All minions which begin with the strings 'nag1' or any minion with
    # a grain set called 'role' with the value of 'monitoring' will have
    # the 'server.sls' state file applied from the 'nagios/' directory.

    'nag1* or G@role:monitoring':
        - match: compound
        - nagios.server

How Top Files Are Compiled

When a highstate is executed and an environment is specified (either using the environment config option or by passing the saltenv when executing the highstate), then that environment's top file is the only top file used to assign states to minions, and only states from the specified environment will be run.

The remainder of this section applies to cases in which a highstate is executed without an environment specified.

With no environment specified, the minion will look for a top file in each environment, and each top file will be processed to determine the SLS files to run on the minions. By default, the top files from each environment will be merged together. In configurations with many environments, such as with GitFS where each branch and tag is treated as a distinct environment, this may cause unexpected results as SLS files from older tags cause defunct SLS files to be included in the highstate. In cases like this, it can be helpful to set top_file_merging_strategy to same to force each environment to use its own top file.

top_file_merging_strategy: same

Another option would be to set state_top_saltenv to a specific environment, to ensure that any top files in other environments are disregarded:

state_top_saltenv: base

With GitFS, it can also be helpful to simply manage each environment's top file separately, and/or manually specify the environment when executing the highstate to avoid any complicated merging scenarios. gitfs_env_whitelist and gitfs_env_blacklist can also be used to hide unneeded branches and tags from GitFS to reduce the number of top files in play.

When using multiple environments, it is not necessary to create a top file for each environment. The easiest-to-maintain approach is to use a single top file placed in the base environment. This is often infeasible with GitFS though, since branching/tagging can easily result in extra top files. However, when only the default (roots) fileserver backend is used, a single top file in the base environment is the most common way of configuring a highstate.

The following minion configuration options affect how top files are compiled when no environment is specified, it is recommended to follow the below four links to learn more about how these options work:

Top File Compilation Examples

For the scenarios below, assume the following configuration:

/etc/salt/master:

file_roots:
  base:
    - /srv/salt/base
  dev:
    - /srv/salt/dev
  qa:
    - /srv/salt/qa

/srv/salt/base/top.sls:

base:
  '*':
    - base1
dev:
  '*':
    - dev1
qa:
  '*':
    - qa1

/srv/salt/dev/top.sls:

base:
  'minion1':
    - base2
dev:
  'minion2':
    - dev2
qa:
  '*':
    - qa1
    - qa2

Note

For the purposes of these examples, there is no top file in the qa environment.

Scenario 1 - dev Environment Specified

In this scenario, the highstate was either invoked with saltenv=dev or the minion has environment: dev set in the minion config file. The result will be that only the dev2 SLS from the dev environment will be part of the highstate, and it will be applied to minion2, while minion1 will have no states applied to it.

If the base environment were specified, the result would be that only the base1 SLS from the base environment would be part of the highstate, and it would be applied to all minions.

If the qa environment were specified, the highstate would exit with an error.

Scenario 2 - No Environment Specified, top_file_merging_strategy is "merge"

In this scenario, assuming that the base environment's top file was evaluated first, the base1, dev1, and qa1 states would be applied to all minions. If, for instance, the qa environment is not defined in /srv/salt/base/top.sls, then because there is no top file for the qa environment, no states from the qa environment would be applied.

Scenario 3 - No Environment Specified, top_file_merging_strategy is "same"

Changed in version 2016.11.0: In prior versions, "same" did not quite work as described below (see here). This has now been corrected. It was decided that changing something like top file handling in a point release had the potential to unexpectedly impact users' top files too much, and it would be better to make this correction in a feature release.

In this scenario, base1 from the base environment is applied to all minions. Additionally, dev2 from the dev environment is applied to minion2.

If default_top is unset (or set to base, which happens to be the default), then qa1 from the qa environment will be applied to all minions. If default_top were set to dev, then both qa1 and qa2 from the qa environment would be applied to all minions.

Scenario 4 - No Environment Specified, top_file_merging_strategy is "merge_all"

New in version 2016.11.0.

In this scenario, all configured states in all top files are applied. From the base environment, base1 would be applied to all minions, with base2 being applied only to minion1. From the dev environment, dev1 would be applied to all minions, with dev2 being applied only to minion2. Finally, from the qa environment, both the qa1 and qa2 states will be applied to all minions. Note that the qa1 states would not be applied twice, even though qa1 appears twice.