pod-cpu-hog.md

id	title	sidebar_label
pod-cpu-hog	Pod CPU Hog Details	Pod CPU Hog

---

Experiment Metadata

Type	Description	Tested K8s Platform
Generic	Consume CPU resources on the application container	GKE, Packet(Kubeadm), Minikube, EKS, AKS

Prerequisites

• Ensure that Kubernetes Version > 1.16
• Ensure that the Litmus Chaos Operator is running by executing kubectl get pods in operator namespace (typically, litmus). If not, install from here
• Ensure that the pod-cpu-hog experiment resource is available in the cluster by executing kubectl get chaosexperiments in the desired namespace. If not, install from here

Entry Criteria

• Application pods are healthy on the respective nodes before chaos injection

Exit Criteria

• Application pods are healthy on the respective nodes post chaos injection

Details

• This experiment consumes the CPU resources on the application container on specified number of cores
• It simulates conditions where app pods experience CPU spikes either due to expected/undesired processes thereby testing how the overall application stack behaves when this occurs.
• Causes CPU resource consumption on specified application containers using cgroups and litmus nsutil which consume CPU resources of the given target containers.
• It can test the application's resilience to potential slowness/unavailability of some replicas due to high CPU load

Integrations

• Pod CPU Hog can be effected using the chaos library: litmus

Steps to Execute the Chaos Experiment

• This Chaos Experiment can be triggered by creating a ChaosEngine resource on the cluster. To understand the values to provide in a ChaosEngine specification, refer Getting Started

• Follow the steps in the sections below to create the chaosServiceAccount, prepare the ChaosEngine & execute the experiment.

Prepare chaosServiceAccount

Use this sample RBAC manifest to create a chaosServiceAccount in the desired (app) namespace. This example consists of the minimum necessary role permissions to execute the experiment.

Sample Rbac Manifest

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: pod-cpu-hog-sa
  namespace: default
  labels:
    name: pod-cpu-hog-sa
    app.kubernetes.io/part-of: litmus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: pod-cpu-hog-sa
  namespace: default
  labels:
    name: pod-cpu-hog-sa
    app.kubernetes.io/part-of: litmus
rules:
- apiGroups: [""]
  resources: ["pods","events"]
  verbs: ["create","list","get","patch","update","delete","deletecollection"]
- apiGroups: [""]
  resources: ["pods/exec","pods/log","replicationcontrollers"]
  verbs: ["create","list","get"]
- apiGroups: ["batch"]
  resources: ["jobs"]
  verbs: ["create","list","get","delete","deletecollection"]
- apiGroups: ["apps"]
  resources: ["deployments","statefulsets","daemonsets","replicasets"]
  verbs: ["list","get"]
- apiGroups: ["apps.openshift.io"]
  resources: ["deploymentconfigs"]
  verbs: ["list","get"]
- apiGroups: ["argoproj.io"]
  resources: ["rollouts"]
  verbs: ["list","get"]
- apiGroups: ["litmuschaos.io"]
  resources: ["chaosengines","chaosexperiments","chaosresults"]
  verbs: ["create","list","get","patch","update"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: pod-cpu-hog-sa
  namespace: default
  labels:
    name: pod-cpu-hog-sa
    app.kubernetes.io/part-of: litmus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: pod-cpu-hog-sa
subjects:
- kind: ServiceAccount
  name: pod-cpu-hog-sa
  namespace: default

Note: In case of restricted systems/setup, create a PodSecurityPolicy(psp) with the required permissions. The chaosServiceAccount can subscribe to work around the respective limitations. An example of a standard psp that can be used for litmus chaos experiments can be found here.

Prepare ChaosEngine

• Provide the application info in spec.appinfo
• Override the experiment tunables if desired in experiments.spec.components.env
• To understand the values to provided in a ChaosEngine specification, refer ChaosEngine Concepts

Supported Experiment Tunables

Variables	Description	Type	Notes
CPU_CORES	Number of the cpu cores subjected to CPU stress	Optional	Default to 1
TOTAL_CHAOS_DURATION	The time duration for chaos insertion (seconds)	Optional	Default to 60s
LIB	The chaos lib used to inject the chaos. Available libs are litmus and pumba	Optional	Default to litmus
LIB_IMAGE	Image used to run the helper pod.	Optional	Defaults to litmuschaos/go-runner:1.13.8
STRESS_IMAGE	Container run on the node at runtime by the pumba lib to inject stressors. Only used in LIB pumba	Optional	Default to alexeiled/stress-ng:latest-ubuntu
TARGET_PODS	Comma separated list of application pod name subjected to pod cpu hog chaos	Optional	If not provided, it will select target pods randomly based on provided appLabels
TARGET_CONTAINER	Name of the target container under chaos.	Optional	If not provided, it will select the first container of the target pod
PODS_AFFECTED_PERC	The Percentage of total pods to target	Optional	Defaults to 0 (corresponds to 1 replica), provide numeric value only
CONTAINER_RUNTIME	container runtime interface for the cluster	Optional	Defaults to docker, supported values: docker, containerd and crio for litmus and only docker for pumba LIB
SOCKET_PATH	Path of the containerd/crio/docker socket file	Optional	Defaults to `/var/run/docker.sock`
RAMP_TIME	Period to wait before and after injection of chaos in sec	Optional
SEQUENCE	It defines sequence of chaos execution for multiple target pods	Optional	Default value: parallel. Supported: serial, parallel
INSTANCE_ID	A user-defined string that holds metadata/info about current run/instance of chaos. Ex: 04-05-2020-9-00. This string is appended as suffix in the chaosresult CR name.	Optional	Ensure that the overall length of the chaosresult CR is still < 64 characters

Sample ChaosEngine Manifest

apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: nginx-chaos
  namespace: default
spec:
  # It can be active/stop
  engineState: 'active'
  appinfo:
    appns: 'default'
    applabel: 'app=nginx'
    appkind: 'deployment'
  chaosServiceAccount: pod-cpu-hog-sa
  experiments:
    - name: pod-cpu-hog
      spec:
        components:
          env:
            - name: TOTAL_CHAOS_DURATION
              value: '60' # in seconds

            - name: CPU_CORES
              value: '1'    

            ## Percentage of total pods to target
            - name: PODS_AFFECTED_PERC
              value: ''   

            ## provide the cluster runtime
            - name: CONTAINER_RUNTIME
              value: 'docker'        

            # provide the socket file path
            - name: SOCKET_PATH
              value: '/var/run/docker.sock'    

Create the ChaosEngine Resource

• Create the ChaosEngine manifest prepared in the previous step to trigger the Chaos.

  kubectl apply -f chaosengine.yml

• If the chaos experiment is not executed, refer to the troubleshooting section to identify the root cause and fix the issues.

Watch Chaos progress

• Set up a watch on the applications interacting/dependent on the affected pods and verify whether they are running

  watch kubectl get pods -n <application-namespace>

• Verify the resource consumption

  kubectl top pod <target-pod-name> -n <application-namespace>

Abort/Restart the Chaos Experiment

• To stop the pod-cpu-hog experiment immediately, either delete the ChaosEngine resource or execute the following command:

  kubectl patch chaosengine <chaosengine-name> -n <namespace> --type merge --patch '{"spec":{"engineState":"stop"}}'

• To restart the experiment, either re-apply the ChaosEngine YAML or execute the following command:

  kubectl patch chaosengine <chaosengine-name> -n <namespace> --type merge --patch '{"spec":{"engineState":"active"}}'

Check Chaos Experiment Result

• Check whether the application stack is resilient to CPU spikes on the app replica, once the experiment (job) is completed. The ChaosResult resource name is derived like this: <ChaosEngine-Name>-<ChaosExperiment-Name>.

  kubectl describe chaosresult nginx-chaos-pod-cpu-hog -n <application-namespace>

Pod CPU Hog Experiment Demo

• A sample recording of this experiment execution is provided here.