OpenCrowbar Design Principles: Attribute Injection [Series 6 of 6]

This is part 5 of 6 in a series discussing the principles behind the “ready state” and other concepts implemented in OpenCrowbar.  The content is reposted from the OpenCrowbar docs repo.

Attribute Injection

Attribute Injection is an essential aspect of the “FuncOps” story because it helps clean boundaries needed to implement consistent scripting behavior between divergent sites.

attribute_injectionIt also allows Crowbar to abstract and isolate provisioning layers. This operational approach means that deployments are composed of layered services (see emergent services) instead of locked “golden” images. The layers can be maintained independently and allow users to compose specific configurations a la cart. This approach works if the layers have clean functional boundaries (FuncOps) that can be scoped and managed atomically.

To explain how Attribute Injection accomplishes this, we need to explore why search became an anti-pattern in Crowbar v1. Originally, being able to use server based search functions in operational scripting was a critical feature. It allowed individual nodes to act as part of a system by searching for global information needed to make local decisions. This greatly added Crowbar’s mission of system level configuration; however, it also created significant hidden interdependencies between scripts. As Crowbar v1 grew in complexity, searches became more and more difficult to maintain because they were difficult to correctly scope, hard to centrally manage and prone to timing issues.

Crowbar was not unique in dealing with this problem – the Attribute Injection pattern has become a preferred alternative to search in integrated community cookbooks.

Attribute Injection in OpenCrowbar works by establishing specific inputs and outputs for all state actions (NodeRole runs). By declaring the exact inputs needed and outputs provided, Crowbar can better manage each annealing operation. This control includes deployment scoping boundaries, time sequence of information plus override and substitution of inputs based on execution paths.

This concept is not unique to Crowbar. It has become best practice for operational scripts. Crowbar simply extends to paradigm to the system level and orchestration level.

Attribute Injection enabled operations to be:

  • Atomic – only the information needed for the operation is provided so risk of “bleed over” between scripts is minimized. This is also a functional programming preference.
  • Isolated Idempotent – risk of accidentally picking up changed information from previous runs is reduced by controlling the inputs. That makes it more likely that scripts can be idempotent.
  • Cleanly Scoped – information passed into operations can be limited based on system deployment boundaries instead of search parameters. This allows the orchestration to manage when and how information is added into configurations.
  • Easy to troubleshoot – since the information is limited and controlled, it is easier to recreate runs for troubleshooting. This is a substantial value for diagnostics.

5 things keeping DevOps from playing well with others (Chef, Crowbar and Upstream Patterns)

Sharing can be hardSince my earliest days on the OpenStack project, I’ve wanted to break the cycle on black box operations with open ops. With the rise of community driven DevOps platforms like Opscode Chef and Puppetlabs, we’ve reached a point where it’s both practical and imperative to share operational practices in the form of code and tooling.

Being open and collaborating are not the same thing.

It’s a huge win that we can compare OpenStack cookbooks. The real victory comes when multiple deployments use the same trunk instead of forking.

This has been an objective I’ve helped drive for OpenStack (with Matt Ray) and it has been the Crowbar objective from the start and is the keystone of our Crowbar 2 work.

This has proven to be a formidable challenge for several reasons:

  1. diverging DevOps patterns that can be used between private, public, large, small, and other deployments -> solution: attribute injection pattern is promising
  2. tooling gaps prevent operators from leveraging shared deployments -> solution: this is part of Crowbar’s mission
  3. under investing in community supporting features because they are seen as taking away from getting into production -> solution: need leadership and others with join
  4. drift between target versions creates the need for forking even if the cookbooks are fundamentally the same -> solution: pull from source approaches help create distro independent baselines
  5. missing reference architectures interfere with having a stable baseline to deploy against -> solution: agree to a standard, machine consumable RA format like OpenStack Heat.

Unfortunately, these five challenges are tightly coupled and we have to progress on them simultaneously. The tooling and community requires patterns and RAs.

The good news is that we are making real progress.

Judd Maltin (@newgoliath), a Crowbar team member, has documented the emerging Attribute Injection practice that Crowbar has been leading. That practice has been refined in the open by ATT and Rackspace. It is forming the foundation of the OpenStack cookbooks.

Understanding, discussing and supporting that pattern is an important step toward accelerating open operations. Please engage with us as we make the investments for open operations and help us implement the pattern.