OS build model

An OS build names an operating system once, then maps that name to the image or template each resource handler needs

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An OS build is an instance of externalcontent.models.OSBuild. It lets a user pick Windows Server 2022 without knowing that it means one AMI in AWS and a different template in vCenter.

Diagram of one OS build mapped to a different image or template on each resource handler.

Mapping a build to provider images

Each pairing of an OS build with a technology that can provide it is an OSBuildAttribute, whose template_name field holds the provider’s identifier for the image or template. They have the global ID prefix IMG.

OSBuildAttribute is sub-typed, meaning the returned object is a technology-specific subclass with extra fields: AmazonMachineImage for AWS, AzureARMImage for Azure Resource Manager, VsphereOSBuildAttribute for vCenter. Call cast() to reach those fields.

Where a build is offered

OSBuild.environments decides which environments offer the build; from an environment, read environment.os_builds. Applications declare the builds they can be installed on as Application.os_builds; from a build, read os_build.application_set.

Two fields shape how a server is built:

  • use_handler_template, labeled Use Template Provisioning, provisions from the handler’s template rather than building the server from scratch, and stops a provisioning engine from being asked to install the operating system. Builds created in the Add OS Build dialog are template-based.
  • os_family is what is_windows() and is_linux() test, by walking up to the root of the family tree. Use them instead of parsing the build’s name.