1.10. Pod disruption budgets

Understand and configure pod disruption budgets.

1.10.1. Understanding how to use pod disruption budgets to specify the number of pods that must be up

A pod disruption budget is part of the Kubernetes API, which can be managed with oc commands like other object types. They allow the specification of safety constraints on pods during operations, such as draining a node for maintenance.

PodDisruptionBudget is an API object that specifies the minimum number or percentage of replicas that must be up at a time. Setting these in projects can be helpful during node maintenance (such as scaling a cluster down or a cluster upgrade) and is only honored on voluntary evictions (not on node failures).

A PodDisruptionBudget object’s configuration consists of the following key parts:

  • A label selector, which is a label query over a set of pods.

  • An availability level, which specifies the minimum number of pods that must be available simultaneously, either:

    • minAvailable is the number of pods must always be available, even during a disruption.
    • maxUnavailable is the number of pods can be unavailable during a disruption.
注意

A maxUnavailable of 0% or 0 or a minAvailable of 100% or equal to the number of replicas is permitted but can block nodes from being drained.

You can check for pod disruption budgets across all projects with the following: 

$ oc get poddisruptionbudget --all-namespaces

Example output

NAMESPACE         NAME          MIN-AVAILABLE   SELECTOR
another-project   another-pdb   4               bar=foo
test-project      my-pdb        2               foo=bar

The PodDisruptionBudget is considered healthy when there are at least minAvailable pods running in the system. Every pod above that limit can be evicted.

注意

Depending on your pod priority and preemption settings, lower-priority pods might be removed despite their pod disruption budget requirements.

1.10.2. Specifying the number of pods that must be up with pod disruption budgets

You can use a PodDisruptionBudget object to specify the minimum number or percentage of replicas that must be up at a time.

Procedure

To configure a pod disruption budget:

  1. Create a YAML file with the an object definition similar to the following: 

    apiVersion: policy/v1beta1 1
kind: PodDisruptionBudget
metadata:
  name: my-pdb
spec:
  minAvailable: 2  2
  selector:  3
    matchLabels:
      foo: bar
    1
    PodDisruptionBudget is part of the policy/v1beta1 API group.
    2
    The minimum number of pods that must be available simultaneously. This can be either an integer or a string specifying a percentage, for example, 20%.
    3
    A label query over a set of resources. The result of matchLabels and matchExpressions are logically conjoined.

    Or: 

    apiVersion: policy/v1beta1 1
kind: PodDisruptionBudget
metadata:
  name: my-pdb
spec:
  maxUnavailable: 25% 2
  selector: 3
    matchLabels:
      foo: bar
    1
    PodDisruptionBudget is part of the policy/v1beta1 API group.
    2
    The maximum number of pods that can be unavailable simultaneously. This can be either an integer or a string specifying a percentage, for example, 20%.
    3
    A label query over a set of resources. The result of matchLabels and matchExpressions are logically conjoined.

  2. Run the following command to add the object to project: 

    $ oc create -f </path/to/file> -n <project_name>