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HA Support for Tekton Pipeline Controllers

Overview

This document is aimed at helping Cluster Admins when configuring High Availability(HA) support for the Tekton Pipeline controller deployment.

HA support allows components to remain operational when a disruption occurs. This is achieved by following an active/active model, where all replicas of the Tekton controller can receive workload. In this HA approach the reconcile space is distributed across buckets, where each replica owns a subset of those buckets and can process the load if the given replica is the leader of that bucket.

By default HA is enabled in the Tekton pipelines controller.

Configuring HA

In order to achieve HA, the number of replicas for the Tekton Pipeline controller should be greater than one. This allows other instance(s) to take over in case of any disruption on the current active controller.

Configuring the controller replicas

You can modify the replicas number in the controller deployment under spec.replicas or apply an update to a running deployment:

kubectl -n tekton-pipelines scale deployment tekton-pipelines-controller --replicas=3

Configuring the Leader Election

The leader election can be configured via the config-leader-election.yaml. The configmap defines the following parameters:

Parameter Default
data.buckets 1
data.leaseDuration 15s
data.renewDeadline 10s
data.retryPeriod 2s

Note: When setting data.buckets, the underlying Knative library only allows a value between 1 and 10, making 10 the maximum number of allowed buckets.

Disabling leader election

If HA is not required and running a single instance of the Tekton Pipeline controller is enough, there are two alternatives:

Use the disable-ha flag

You can modify the controller deployment, by specifying in the tekton-pipelines-controller container the disable-ha flag. For example:

spec:
  serviceAccountName: tekton-pipelines-controller
  containers:
  - name: tekton-pipelines-controller
    ...
    args: [
      # Other flags defined here...
      "-disable-ha=true"
    ]

by setting disable-ha to true, HA will be disable in the controllers.

Note: Please consider that when disabling HA and keeping multiple replicas of the controller deployment, each replica will act as an independent controller, leading to an unwanted behaviour when creating resources(e.g. TaskRuns, etc).

Scale down your replicas

Although HA is enable by default, if your controller deployment replicas are set to one, there would be no High Availability in the scenario where the running instance is deleted or fails. Therefore having a single replica even with HA enable, does not ensure high availability for the controller.