Cluster Retraction

Objective

This guide provides instructions on how to configure fallback in case of endpoints behind a cluster that are not healthy. Cluster groups a set of endpoints together into a resource pool that is used in the load balancer configuration. To know more concepts about the endpoints and load balancer, see Load Balancing and Service Mesh.

When a route points to multiple clusters as part of weighted cluster configuration and any of the clusters have no healthy endpoints, then traffic to the route is distributed only among the remaining clusters that have one or more healthy endpoints. This is called as cluster retracting. An endpoint is deemed unhealthy in case health-check fails or endpoint discovery fails.

Using the instructions provided in this guide, you can enable or disable cluster retraction for a HTTP or TCP load balancer.

Note: Cluster retraction is enabled by default for HTTP and TCP load balancers. This also means that weighted cluster configuration of route and panic-threshold configuration of cluster may not work when any cluster gets retracted because of no healthy endpoints.

Prerequisites

The following prerequisites apply:


Configuration

Cluster retraction is enabled by default for HTTP and TCP load balancers. You can disable it while creating a new load balancer or you can enable or disable it for an existing load balancer. This example shows how to update an existing load balancer to enable or disable cluster retraction for a HTTP load balancer.

Perform the following steps to enable or disable cluster retraction

Step 1: Log into the VoltConsole and navigate to the load balancer configuration.
  • Change to your application namespace. Select Manage in the configuration menu and Load Balancers -> HTTP Load Balancers in the options.
  • Click ... -> Edit for your HTTP load balancer from the displayed list.
Step 2: Start editing the route configuration.
  • Navigate to the Routes Configuration section and enable Show Advanced Fields option.
  • Click Configure to open route configuration page.
Step 3: Configure cluster retraction.
  • Click Configure under the Advanced Fields section for the route entries for which you want to enable the cluster retraction. This opens the advanced configuration page for the route.
  • Go to Miscellaneous Options section and enable the Show Advanced Fields option.
  • Select one of the following options for the Enable Route Specific Buffering field:

    • Select Retract cluster with no healthy endpoints to enable cluster retraction.
    • Select Disable cluster retraction to disable cluster retraction.

cluster retraction
Figure: Cluster Retraction Settings

  • Click Apply to apply the cluster retraction setting to the route configuration.
  • Click Apply in the route configuration page to apply the changes to load balancer configuration
Step 4:Complete applying cluster retraction to load balancer.

Click Save and Exit in the load balancer page to enable or disable the cluster retraction for that load balancer. Any subsequent endpoint failures result in performing cluster retraction.


Concepts


API References