This document is a draft
The idea was formed around a concept to extend the ability to manage a local system with configuration management tools. The initial idea was put forth by Kevin Fenzi, Infrastructure Lead at the Fedora Project.
This document and repository is my take on how formulas can be implemented.
Formulas provide an better way to manage local configurations.
The primary CM tool supported is ansible, but it is possible to support other CM tools.
A Formula is idempotent, meaning that it can be applied and each time the resulting configuration is the same. The value of this is that one or more machines can use the same Formula and expect the same setup.
Consider the following example as a simple Formula:
* Install the Apache Web Server (httpd) * Add a configuration to create a virtual host * Drop some basic web data, including configuration for a database * Install Mysql (mysql-server) * Start the httpd and mysql services * Sync the database
It may be clear that some of the steps above can be done by a simple yum install or adding a simple script to the %post section in a kickstart. In some cases, however, interactive responses are required, like the username/password of the database, for example. In these cases it may be better to have an interactive prompt at first boot.
Additionally, Formulas could be played back after the initial interactive configuration. Thus providing automation to the process. Answer the questions once, apply the same rules in several other situations quickly and easily.
Simply put, many Formulas will be written. It would seem logical that Formulas should be shared, but with a control structure of some sort. Therefore, a model has been put forth to manage 'approved' Formulas, by which a trust can be formed between the infrastructure provider and those applying Formulas. Formulas will exist in a git repository which is tightly managed for writes by gitolite. This will provide a level of assurance that any Formula being applied from the 'approved' set can be applied reliably each time.
Additionally, it would make sense that a read-only form of these git repositories would exist to provide an easy mechanism for sharing. Because the goal is to encourage more 'approved' Formulas, as well as provide a means for testing, expanding and even maintaining a separate set of Formulas, a git forking model has been adopted.
With the exception of the 'approved' repositories being managed in some form of review and approval process, likely similar to the Fedora RPM approval model, git repositories can be forked and modified much like how they are on github. The fork and pull request model works well because the control remains with the upstream repository. In this case, it proves valuable because when any Formula is improved upon, it can be merged back into the upstream repository at the maintainer's convenience or not at all.
Formulas can be applied to any Linux system as long as it is a supported configuration management system. This currently means that it '''must''' be ansible, but more are likely to come.
To apply a Formula, it must exist on the local system in an archive. A Formula is applied as follows:
# formulas apply formula_one
Formulas can be downloaded from remote sources to the local system as part of the apply command. Remote sources can be configured in the Formulas.conf. Multiple sources can be searched in the order provided, thus allowing for searching through 'approved' Formulas before others, for example. An example configuration may look something like this:
remote_sources: - git://github.com/herlo/formulas/ - git://github.com/bob/formulas/ - file:///var/lib/formulas/
In this way, if the 'formula_one' Formula existed in both the herlo and bob repositories, the herlo 'formula_one' Formula would be downloaded and applied. If the 'formula_two' were to be applied, the same search would occur, but it's possible that the bob 'formula_two' formula would be the first one found since the 'herlo' repository didn't have a 'formula_two'. Additionally, locations for Formulas can be overridden by a config option:
# formulas apply formula_one --remote_source=file:///var/lib/formulas,file://home/herlo/formulas
Eventually, the hope is to have Formulas available in 'FirstBoot'. In Fedora 18, FirstBoot was replaced by anaconda, probably called 'Stage III'. Because anaconda Stage III now provides this functionality, it is much more flexible than the old FirstBoot. This makes adding a GUI interface for formulas much less complex. To that end, the list of 'approved' Formulas may easily be available and/or configurable at FirstBoot. Having something like this makes Formulas a 'killer' feature for Fedora 18 and beyond.