Module mz_environmentd::deployment

Environment deployments.

A deployment is a graceful transition of an environment to a new version or configuration [^1]. This module provides the components that facilitate these deployments.

Deployments are initiated and driven externally to environmentd. At a very high level, the process works like this:

1. The external orchestrator starts a new environmentd process with a deploy generation that is greater than the previous deploy generation (e.g., if the current deploy generation is 1, the new environmentd process should be started with --deploy-generation=2).

2. The new environmentd process initializes to the extent possible. At the moment the initialization process is quite weak and only validates that the catalog is loadable. We plan to strengthen the initialization process over time to include starting all clusterd processes in the new deployment and ensuring that they rehydrate successfully.

3. The new deployment announces that it is ready to take over from the previous generation (ReadyToPromote) via the internal HTTP server.

4. The external orchestrator promotes the new deployment via the HTTP server.

5. The new deployment completes any remaining initialization tasks and prepares to serve queries.

6. Simultaneously, the external orchestrator tears down the old deployment.

[^1] “Configuration” here means “command-line flags”. Most settings in an environment are changeable at runtime via LaunchDarkly feature flags, but occasionally we have settings that are only changeable via command-line flags to environmentd. Changing these flags requires a process restart, and performing that process restart without incurring unavailability requires this deployment infrastructure.

Modules

• preflight
  Preflight checks for deployments.
• state
  Deployment state handling.