Bulding CFEngine classes using EFL

Tags: cfengine EFL

Recently my CFEngine colleague Marco Marongiu wrote about classifying CFEngine hosts via external means. His post inspired me to write about classifying hosts using EFL.

EFL allows you classify your hosts using data separation and external modules. Let's look at the current bundles available to you and how you can expand EFL adding your own.

All of these bundles take a CSV file as a parameter. You can call the bundles when, where, and as many times as you like using different parameter files. For the sake of readability I’m going to break long lines in these examples using ‘\’. You cannot do this in actual use because the CFEngine functions that read CSV files treat line breaks as record breaks.

Classes from hostnames

If you have an arbitrary list of hosts that you’d like to belong to the same class then you can use the bundle efl_class_hostname. In this example assume the desired class is web_servers. Create a file called efl_class_hostname-web_servers.txt and fill it with a list of unqualified hostnames, one per line, of all the hosts that belong to the class web_servers.

$ cat efl_class_hostname-webservers.txt
atlweb01
atlweb01
dmzatlweb01
dmzatlweb02
altdevweb01
atltestweb02

The bundle efl_class_hostname extracts the class name web_servers from the file name using ‘-’ and ‘.txt’ as anchors. The bundle then iterates through each line in the file. If any line in the file matches ${sys.uqhost} the class web_servers is set in the scope of namespace, which is less accurately called a global class.

Call the bundle via method.

"Set web_server class"
   usebundle => efl_class_hostname( "${sys.workdir}/inputs/efl_class_hostname-web_servers.txt" );

Classes from reading external command output

The bundle efl_class_cmd_regcmp defines a class if the output of a command matches, or does not match, the provided regular expression. Consider the following parameter file. It has seven columns from zero to six.

Zero is the constraining class expression. The record is only promised if this class expression is true.
One is the class promiser that will be set.
Two is whether or not to negate the match. Meaning set a class if the expression is not matched.
Three is the command to run.
Four defines whether or not the command is run in a full shell.
Five is the regular expression that must match the entire output of the command in four.
Six is a free form promisee for documentation and searching.

Define global class if anchored regex matches command output.

context(0) ;; class promiser(1) ;; 'not' match?(2) ;; command(3) ;; useshell/noshell(4) ;; anchored regex(5) ;; promisee(6)

debian ;; install_cfengine_apt_key ;; yes ;; /usr/bin/apt-key list ;; useshell ;; (?ims).?CFEngine Community package repository. ;; Neil Watson

The above record runs the command 'apt-key list' on hosts of the debian class. If the given regular expression is not matched (see column two), then the class 'install_cfengine_apt_key' is set.