pdb-controller

README

Pod Disruption Budget Controller

This is a simple Kubernetes controller for adding default Pod Disruption Budgets (PDBs) for Deployments and StatefulSets in case none are defined. This is inspired by the dicussion in kubernetes/kubernetes#35318 and was created for lack of an alternative.

How it works

The controller simply gets all Pod Disruption Budgets for each namespace and compares them to Deployments and StatefulSets. For any resource with more than 1 replica and no matching Pod Disruption Budget, a default PDB will be created:

apiVersion: policy/v1beta1
kind: PodDisruptionBudget
metadata:
  name: my-app
  namespace: kube-system
  labels:
    application: my-app
    heritage: pdb-controller
    version: v1.0.0
spec:
  minAvailable: 1
  selector:
    matchLabels:
      application: my-app

The selector and labels are based on those from the related Deployment or StatefulSet. The special heritage=pdb-controller label is set by the controller and is used to find owned PDBs. Owned PDBs are removed in case replicas of the related resource is scaled to 1 or less. This is done to prevent deadlocking for clients depending on the PDBs e.g. cluster upgrade tools.

Additionally you can run the controller with the flag --non-ready-ttl=15m which means it will remove owned PDBs in case the pods of a targeted deployment or statefulset are non-ready for more than the specified ttl. This is another way to ensure broken deployments doesn't block cluster operations.

This global value can also be overriden by specifying the annotation pdb-controller.zalando.org/non-ready-ttl on a deployment or statefulset.

Building

This project uses Go modules as introduced in Go 1.11 therefore you need Go >=1.11 installed in order to build. If using Go 1.11 you also need to activate Module support.

Assuming Go has been setup with module support it can be built simply by running:

export GO111MODULE=on # needed if the project is checked out in your $GOPATH.
$ make

Setup

The pdb-controller can be run as a deployment in the cluster. See deployment.yaml for an example.

Deploy it by running:

$ kubectl apply -f docs/deployment.yaml

TODO

• Instead of long polling, add a Watch feature.

LICENSE

See LICENSE file.