Plugin Broker refactoring

This issue is to collect the various open design-level issues for the plugin broker and discuss the path forward.

Current Issues

• [1] Merge plugin brokers into a single image: https://github.com/eclipse/che/issues/14296
• [2] Plugin broker should only make necessary changes to plugins: https://github.com/eclipse/che/issues/13452
• [3] Plugin broker as separate service shared among workspaces: https://github.com/redhat-developer/rh-che/issues/1592
• [4] REST backend/merge plugin and devfile registries: https://github.com/eclipse/che/issues/14268
• [5] Broker’s role as a library in Che Operator

Current broker functionality

The current version of the plugin broker (v0.20), broadly, does two things:

• Compute workspace metadata changes necessary to run the requested plugins (e.g. env vars, sidecars, etc.)
• Download extension artifacts so that Theia/VSCode plugins can be run.

This is done in one image (ignoring the init broker for now); the broker takes plugin FQNs, downloads meta.yamls, converts those meta.yamls to Che Plugins, and downloads their artifacts.

Proposed changes

The plugin broker should be refactored into two images with separate concerns;

• One image (a metadata broker) is only responsible for computing Che Plugins from meta.yamls and returning that information to the Che server so that the workspace can be provisioned
• One image (an “artifact” broker) is only responsible for ensuring any files needed for plugins are present in their appropriate folders (/plugins or /plugins/sidecars)

A proof-of-concept implementation is available in my fork: https://github.com/eclipse/che-plugin-broker/compare/master...amisevsk:refactor-brokers?ts=4

These changes would address the issues listed above

• Plugin broker as separate service shared among workspaces: Separating out the metadata actions is a necessary step in having a shared “plugin broker” service; the artifact broker will always have to exist, as something has to mount /plugins to download artifacts. The metadata broker could easily be adapted into a library or service that runs separate from workspace starts/stops
• REST backend/merge plugin and devfile registries: The metadata broker could be integrated into the plugin-registry REST backend, allowing the registry to precompute/cache Che Plugins without running a separate image.
• Broker’s role as a library in Che Operator: The adapted brokers are API compatible with the unified broker, so the metadata broker can be used as a library. It also avoids the need to specify “only metadata actions” when running the broker, since the metadata broker is always “only metadata actions”
• Merge plugin brokers into a single image: The goal of a single image has issues with the other goals listed above; the metadata broker, if integrated into e.g. the registry, could be removed, leaving us with one image as hoped
• Plugin broker should only make necessary changes to plugins: Since the refactor removes the init broker, it would be fairly simple to add this functionality to the artifact broker.

Additionally, one improvement with this approach is that it removes the clumsy way we run the broker in ephemeral workspaces (run the entire broker and download everything twice). The metadata broker can run separately to get the workspace configuration information, and then the artifact broker can run as an init container on the workspace pod.

Alternatives

One goal would be to get rid of the plugin broker altogether. This would likely involve reworking Theia to do this fetching at startup. Even in this case, the refactor above would be useful, as it would easily allow separate deprecation of broker functions (i.e. we could deprecate/move the metadata broker to the registry and deprecate the artifact broker when Theia has this functionality).

Summary

Workspace startup with and without changes (ephemeral workspace to show worst-case process):

[amisevsk]

The relevant PRs are finally open:

• Plugin brokers: https://github.com/eclipse/che-plugin-broker/pull/80
• Che server: https://github.com/eclipse/che/pull/15386

Changes can be tested by starting a Che server using the CI image eclipseche/che-server:15386 and adding env vars:

CHE_WORKSPACE_PLUGIN__BROKER_METADATA_IMAGE=amisevsk/che-metadata-plugin-broker:dev
CHE_WORKSPACE_PLUGIN__BROKER_ARTIFACTS_IMAGE=amisevsk/che-artifacts-plugin-broker:dev

[nickboldt]

Moved to milestone 7.8 as that’s where it was delivered. “Backlog” makes it seem like it wasn’t done. 😃