10/18 Update:

More recent information about Barclamps can be found at https://robhirschfeld.com/2011/09/14/details-of-crowbar-changes/.  We’ve also created videos showing how you can create your own barclamps.

Original Post

Just after we’d started deep Crowbar development, Andi Abes, Paul Webster and Victor Lowther joined the Dell Crowbar+OpenStack team.  They immediately started to dig into our Swift, BIOS/RAID, and Network components.  They also started to bump into each other in our original code base.  It quickly became apparent that we needed to modularize Crowbar.

Restructuring Crowbar into modules has proved essential as a method for safe community collaboration.

Greg Althaus coined the name “barclamps” during the modularization rearchitecture.  A barclamp is a class extension of the Crowbar ServiceObject that allows Crowbar to identify the Chef components used by the barclam

p (name p

attern in Chef is bc-template-[barclamp]) and provides capabilities that are specific to each barclamp.

• In the simplest case, the barclamp is a minimal wrapper that just provides naming hooks for your Chef cookbooks.  This makes it very easily to adapt existing Chef work to work with Crowbar.
• In more complex cases, the barclamp will help identity how nodes are allocated, interacts with other barclamps, extends the provisioner state machine and provides custom user interfaces.
• In most cases, the barclamp’s generic integration and UI are sufficient.

When looking at the barclamps, it is critical to understand that even the most core Crowbar functionality is expressed as a barclamp.