Pod autoscaler

Pod autoscaler is a Kubernetes pod-level chaos fault that determines whether nodes can accomodate multiple replicas of a given application pod. This fault examines the node auto-scaling feature by determining whether the pods were successfully rescheduled within a specified time frame if the existing nodes are running at the specified limits.

Use cases

Pod autoscaler determines how an application accomodates multiple replicas of a given application pod at unexpected times.

Permissions required

Below is a sample Kubernetes role that defines the permissions required to execute the fault.

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: hce
  name: pod-autoscaler
spec:
  definition:
    scope: Cluster # Supports "Namespaced" mode too
permissions:
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["create", "delete", "get", "list", "patch", "deletecollection", "update"]
  - apiGroups: [""]
    resources: ["events"]
    verbs: ["create", "get", "list", "patch", "update"]
  - apiGroups: [""]
    resources: ["pods/log"]
    verbs: ["get", "list", "watch"]
  - apiGroups: [""]
    resources: ["deployments, statefulsets"]
    verbs: ["get", "list", "patch", "update"]
  - apiGroups: [""]
    resources: ["chaosEngines", "chaosExperiments", "chaosResults"]
    verbs: ["create", "delete", "get", "list", "patch", "update"]
  - apiGroups: ["batch"]
    resources: ["jobs"]
    verbs: ["create", "delete", "get", "list", "deletecollection"]

Prerequisites

• Kubernetes > 1.16
• The application pods should be in the running state before and after injecting chaos.

Mandatory tunables

Tunable	Description	Notes
REPLICA_COUNT	Number of replicas you wish to scale to.	nil. For more information, go to replica counts
NODE_LABEL	Node label used to filter the target node if TARGET_NODE environment variable is not set.	It is mutually exclusive with the TARGET_NODE environment variable. If both are provided, the fault uses TARGET_NODE. For more information, go to node label.

Optional tunables

Tunable	Description	Notes
TOTAL_CHAOS_DURATION	Duration for which to insert chaos (in seconds).	Default: 60 s. For more information, go to duration of the chaos.
RAMP_TIME	Period to wait before and after injecting chaos (in seconds).	For example, 30 s. For more information, go to ramp time

Replica counts

Number of replicas that need to be present in the target application during chaos. Tune it by using the REPLICA_COUNT environment variable.

The following YAML snippet illustrates the use of this environment variable:

# provide the number of replicas
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  annotationCheck: "false"
  appinfo:
    appns: "default"
    applabel: "app=nginx"
    appkind: "deployment"
  chaosServiceAccount: litmus-admin
  experiments:
    - name: pod-autoscaler
      spec:
        components:
          env:
            # number of replica, needs to scale
            - name: REPLICA_COUNT
              value: "3"
            - name: TOTAL_CHAOS_DURATION
              VALUE: "60"