tag_manager.rb

TagManager

The TagManager provides a way of querying tags. Tags are keywords associated with a specific hostname or group. These are useful for grouping together hosts and defining common behavior for them.

Basics

The tags are typically stored in a Project‘s config/tags.yml file.

For example, consider this config/tags.yml file:

  desktops:
    - satori
    - sunyata
    - michiru
  notebooks:
    - rheya
    - avijja

With the above file, if we‘re on the host called "satori", we can query the fields like this:

  tags # => ["satori", "desktops", "localhost", ...]

  tagged?("desktops") # => true
  tagged?("notebooks") # => false
  tagged?(:satori) # => true
  tagged?("satori") # => true
  tagged?("satori || desktops") # => true
  tagged?("(satori || desktops) && !notebooks") # => true

Traits

Your system may also automatically add tags that describe your system‘s traits, such as the name of the operating system, distribution release, hardware architecture, hostnames, IP addresses, etc.

For example, here is a full set of tags for a system:

 ai> pp tags.sort                # Pretty print the tags in sorted order
 ["10.0.0.6",                    # IPv4 addresses
  "127.0.0.1",                   # ...
  "192.168.130.1",               # ...
  "::1/128",                     # IPv6 addresses
  "fe80::250:56ff:fec0:8/64",    # ...
  "fe80::250:8dff:fe95:8fe9/64", # ...
  "i686",                        # Hardware architecture
  "linux",                       # OS
  "linux_i686",                  # OS and architecture
  "localhost",                   # Variants of hostname
  "localhost.localdomain",       # ...
  "michiru",                     # ...
  "michiru.koshevoy",            # ...
  "michiru.koshevoy.net",        # ...
  "myapp_servers",               # User defined tags
  "rails_servers",               # ...
  "ubuntu",                      # OS distribution name
  "ubuntu_6.06"]                 # OS distribution name and release version

To execute code only on an Ubuntu system:

  if tagged?("ubuntu")
    # Code will only be run on Ubuntu systems
  end

These additional tags are retrieved from the PlatformManager and AddressManager. If your platform does not provide drivers for these, you will not get these tags. If you‘re on an unsupported platform and do not want to write drivers, you can work around this by manually declaring the missing tags in config/tags.yml on a host-by-host basis.

Inclusion and negation

You can include and negate tags declaratively by giving "@" and "!" prefixes to arguments.

For example, consider this config/tags.yml file:

  apache_servers:
    - kurou
    - shirou
  apache_servers_except_kurou:
    - @apache_servers
    - !kurou

This will produce the following results:

  ai> hosts_tagged_with("apache_servers")
  => ["kurou", "shirou"]
  ai> hosts_tagged_with("apache_servers_except_kurou")
  => ["shirou"]

Required files