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Webhook

The Webhook is an optional component of GoKubeDownscaler. It works by intercepting the creation or update requests of workloads and evaluating them against the defined schedules and configurations. If a workload matches the criteria to be scaled down upon creation or update, the Webhook modifies the creation/update request to set the number of replicas to the target downscale value.

note

Different from the Downscaler, the Webhook only acts on the creation or update of workloads. It does not periodically check and scale workloads like the Downscaler does.

How It Works​

The Webhook operates as follows:

  1. Intercept Requests: The Webhook intercepts the creation or update requests of workloads
  2. Evaluate Workload: The Webhook evaluates the workload against the defined schedules and configurations to determine if it should be scaled down upon creation or update
  3. Modify Workload: If the workload needs to be scaled down, the Webhook modifies the request to set the number of replicas to the target downscale value

The Webhook can only be installed cluster-wide, since it operates at the API server level.

The details of how the Downscaler evaluates workloads and determines scaling actions are covered in the Scopes And Scaling section.

tip

We designed the MutatingWebhookConfiguration process so that it does not block the creation or update of workloads in case of errors, however, during the evaluation process, unexpected errors may occur that are not related to our component, but could instead be caused by Kubernetes. We recommend keeping the failurePolicy field of the MutatingWebhookConfiguration resource set to Ignore (the default value we provided) you can read more inside the Helm Chart documentation and more specifically in this section (in this section).

When to Use the Webhook​

There are a couple of scenarios where using the Webhook is beneficial:

  • Immediate Compliance: It is useful when the organization wants to ensure that all newly created or updated workloads are immediately compliant with the scaling policies defined by the organization.
  • Avoid Short-term Provisioning: When workloads are created or updated during a downtime period, the Webhook can ensure they are downscaled immediately, avoiding short-term node provisioning and deprovisioning (and the associated useless costs)