Augments

Table of Contents

An augments file can be used to define variables and classes to the execution of all CFEngine components before any parsing or evaluation happen. It's a JSON data file, so you should view and edit it with a JSON-aware editor if possible.This is a convenient way to override defaults defined in the Masterfiles Policy Framework without modifying the shipped policy itself.

The file def.json is found like the policy file to be run:

  • with no arguments, it's in $(sys.inputdir)/def.json because $(sys.inputdir)/promises.cf is used
  • with -f /dirname/myfile.cf, it's in /dirname/def.json
  • with -f ./myfile.cf, it's in ./def.json

Values will be expanded, so you can use the variables from Special Variables.

An augments file can contain the following keys:

inputs

Any filenames you put here will appear in the def.augments_inputs variable. The standard set of masterfiles refers to this variable and will autoload those files.

vars

Any variables you put here will be put in the def bundle scope. Thus:

"vars":
{
  "phone": "22-333-4444",
  "myplatform": "$(sys.os)",
}

results in the variable def.phone with value 22-333-4444 being defined, and def.myplatform with the value of your current OS. Again, note that this happens before policy is parsed or evaluated.

You can see the list of variables thus defined in the output of cf-promises --show-vars (see Components and Common Control). They will be tagged with the tag source=augments_file. For instance, the above two variables (assuming you placed the data in $(sys.inputdir)/def.json) result in

cf-promises --show-vars=default:def
...
default:def.myplatform                   linux                                                        source=augments_file
default:def.phone                        22-333-4444                                                  source=augments_file

Variables of other types than string can be defined too, like in this example

"vars" : {
    "str1" : "string 1",
    "num1" : 5,
    "num2" : 3.5
    "slist1" : ["sliststr1", "sliststr2"]
    "array1" : {
        "idx1" : "val1",
        "idx2" : "val2"
    }
}

classes

Any class names you put here will be evaluated and installed as hard classes if they match as a class name or a regular expression. Thus:

"classes":
{
  "my_always": "any",
  "my_other_apache": [ "server[34]", "debian.*" ],
}

results in my_always being always defined. my_other_apache will be defined if the classes server3 or server4 are defined, or if any class starting with debian is defined. You can use any hard classes.

You can see the list of classes thus defined through def.json in the output of cf-promises --show-classes (see Components and Common Control). They will be tagged with the tags source=augments_file,hardclass. For instance, the above two classes result in:

% cf-promises --show-classes=my_
...
my_always                                                    source=augments_file,hardclass
my_other_apache                                              source=augments_file,hardclass

augments

A list of file names that should be merged using mergedata() semantic

Example:

Here we merge a platform specific augments on to the def.json loaded next to the policy entry and see what the resulting variable values will be.

The def.json next to the policy entry:

{
  "vars":{
    "my_var": "defined in def.json",
    "my_other_var": "Defined ONLY in def.json"
  },
  "augments": [
    "/var/cfengine/augments/$(sys.flavor).json"
  ]
}

The platform specific augments on a CentOS 6 host:

/var/cfengine/augments/centos_6.json:

{
  "vars": {
    "my_var": "Overridden in centos_6.json",
    "centos_6_var": "Defined ONLY in centos_6.json"
  }
}

The expected values of the variables defined in the def bundle scope:

R: def.my_var == Overridden in centos_6.json
R: def.my_other_var == Defined ONLY in def.json
R: def.centos_6_var == Defined ONLY in centos_6.json

History

  • 3.12.0 introduced the augments key
  • 3.7.3 back port def.json parsing in core agent and load def.json if present next to policy entry
  • 3.8.2 removed core support for inputs key, load def.json if present next to policy entry
  • 3.8.1 def.json parsing moved from policy to core agent for resolution of classes and variables to be able to affect control bodies
  • 3.7.0 introduced augments concept into the Masterfiles Policy Framework