Pod CPU Hog Exec

Introduction¶

This experiment consumes the CPU resources of the application container
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.

Scenario: Stress the CPU

Pod CPU Hog Exec

Uses¶

View the uses of the experiment

Disk Pressure or CPU hogs is another very common and frequent scenario we find in kubernetes applications that can result in the eviction of the application replica and impact its delivery. Such scenarios that can still occur despite whatever availability aids K8s provides. These problems are generally referred to as "Noisy Neighbour" problems.

Injecting a rogue process into a target container, we starve the main microservice process (typically pid 1) of the resources allocated to it (where limits are defined) causing slowness in application traffic or in other cases unrestrained use can cause node to exhaust resources leading to eviction of all pods.So this category of chaos experiment helps to build the immunity on the application undergoing any such stress scenario

Prerequisites¶

Verify the 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-exec experiment resource is available in the cluster by executing kubectl get chaosexperiments in the desired namespace. If not, install from here

Default Validations¶

View the default validations

The application pods should be in running state before and after chaos injection.

Minimal RBAC configuration example (optional)¶

NOTE

If you are using this experiment as part of a litmus workflow scheduled constructed & executed from chaos-center, then you may be making use of the litmus-admin RBAC, which is pre installed in the cluster as part of the agent setup.

View the Minimal RBAC permissions

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: pod-cpu-hog-exec-sa
  namespace: default
  labels:
    name: pod-cpu-hog-exec-sa
    app.kubernetes.io/part-of: litmus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: pod-cpu-hog-exec-sa
  namespace: default
  labels:
    name: pod-cpu-hog-exec-sa
    app.kubernetes.io/part-of: litmus
rules:
  # Create and monitor the experiment & helper pods
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["create","delete","get","list","patch","update", "deletecollection"]
  # Performs CRUD operations on the events inside chaosengine and chaosresult
  - apiGroups: [""]
    resources: ["events"]
    verbs: ["create","get","list","patch","update"]
  # Fetch configmaps details and mount it to the experiment pod (if specified)
  - apiGroups: [""]
    resources: ["configmaps"]
    verbs: ["get","list",]
  # Track and get the runner, experiment, and helper pods log 
  - apiGroups: [""]
    resources: ["pods/log"]
    verbs: ["get","list","watch"]  
  # for creating and managing to execute comands inside target container
  - apiGroups: [""]
    resources: ["pods/exec"]
    verbs: ["get","list","create"]
  # deriving the parent/owner details of the pod(if parent is anyof {deployment, statefulset, daemonsets})
  - apiGroups: ["apps"]
    resources: ["deployments","statefulsets","replicasets", "daemonsets"]
    verbs: ["list","get"]
  # deriving the parent/owner details of the pod(if parent is deploymentConfig)  
  - apiGroups: ["apps.openshift.io"]
    resources: ["deploymentconfigs"]
    verbs: ["list","get"]
  # deriving the parent/owner details of the pod(if parent is deploymentConfig)
  - apiGroups: [""]
    resources: ["replicationcontrollers"]
    verbs: ["get","list"]
  # deriving the parent/owner details of the pod(if parent is argo-rollouts)
  - apiGroups: ["argoproj.io"]
    resources: ["rollouts"]
    verbs: ["list","get"]
  # for configuring and monitor the experiment job by the chaos-runner pod
  - apiGroups: ["batch"]
    resources: ["jobs"]
    verbs: ["create","list","get","delete","deletecollection"]
  # for creation, status polling and deletion of litmus chaos resources used within a chaos workflow
  - apiGroups: ["litmuschaos.io"]
    resources: ["chaosengines","chaosexperiments","chaosresults"]
    verbs: ["create","list","get","patch","update","delete"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: pod-cpu-hog-exec-sa
  namespace: default
  labels:
    name: pod-cpu-hog-exec-sa
    app.kubernetes.io/part-of: litmus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: pod-cpu-hog-exec-sa
subjects:
- kind: ServiceAccount
  name: pod-cpu-hog-exec-sa
  namespace: default

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.

Experiment tunables¶

check the experiment tunables

Optional Fields

Variables	Description	Notes
CPU_CORES	Number of the cpu cores subjected to CPU stress	Default to 1
TOTAL_CHAOS_DURATION	The time duration for chaos insertion (seconds)	Default to 60s
LIB	The chaos lib used to inject the chaos. Available libs are `litmus`	Default to `litmus`
TARGET_PODS	Comma separated list of application pod name subjected to pod cpu hog chaos	If not provided, it will select target pods randomly based on provided appLabels
TARGET_CONTAINER	Name of the target container under chaos	If not provided, it will select the first container of the target pod
PODS_AFFECTED_PERC	The Percentage of total pods to target	Defaults to 0 (corresponds to 1 replica), provide numeric value only
CHAOS_INJECT_COMMAND	The command to inject the cpu chaos	Default to `md5sum /dev/zero`
CHAOS_KILL_COMMAND	The command to kill the chaos process	Default to `kill $(find /proc -name exe -lname '*/md5sum' 2>&1 \| grep -v 'Permission denied' \| awk -F/ '{print $(NF-1)}')`. Another useful one that generally works (in case the default doesn't) is `kill -9 $(ps afx \| grep "[md5sum] /dev/zero" \| awk '{print $1}' \| tr '\n' ' ')`. In case neither works, please check whether the target pod's base image offers a shell. If yes, identify appropriate shell command to kill the chaos process
RAMP_TIME	Period to wait before injection of chaos in sec
SEQUENCE	It defines sequence of chaos execution for multiple target pods	Default value: parallel. Supported: serial, parallel

Experiment Examples¶

Common and Pod specific tunables¶

Refer the common attributes and Pod specific tunable to tune the common tunables for all experiments and pod specific tunables.

CPU Cores¶

It stresses the CPU_CORE cpu cores of the targeted pod for the TOTAL_CHAOS_DURATION duration.

Use the following example to tune this:

# cpu cores for the stress
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  annotationCheck: "false"
  appinfo:
    appns: "default"
    applabel: "app=nginx"
    appkind: "deployment"
  chaosServiceAccount: pod-cpu-hog-exec-sa
  experiments:
  - name: pod-cpu-hog-exec
    spec:
      components:
        env:
        # cpu cores for stress
        - name: CPU_CORES
          value: '1'
        - name: TOTAL_CHAOS_DURATION
          value: '60'

Chaos Inject and Kill Commands¶

It defines the CHAOS_INJECT_COMMAND and CHAOS_KILL_COMMAND ENV to set the chaos inject and chaos kill commands respectively. Default values of commands:

CHAOS_INJECT_COMMAND: "md5sum /dev/zero"
CHAOS_KILL_COMMAND: "kill $(find /proc -name exe -lname '*/md5sum' 2>&1 | grep -v 'Permission denied' | awk -F/ '{print $(NF-1)}')"

Use the following example to tune this:

# provide the chaos kill, used to kill the chaos process
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  annotationCheck: "false"
  appinfo:
    appns: "default"
    applabel: "app=nginx"
    appkind: "deployment"
  chaosServiceAccount: pod-cpu-hog-exec-sa
  experiments:
  - name: pod-cpu-hog-exec
    spec:
      components:
        env:
        # command to create the md5sum process to stress the cpu
        - name: CHAOS_INJECT_COMMAND
          value: 'md5sum /dev/zero'
        # command to kill the md5sum process
        # alternative command: "kill -9 $(ps afx | grep "[md5sum] /dev/zero" | awk '{print $1}' | tr '\n' ' ')"
        - name: CHAOS_KILL_COMMAND
          value: "kill $(find /proc -name exe -lname '*/md5sum' 2>&1 | grep -v 'Permission denied' | awk -F/ '{print $(NF-1)}')"
        - name: TOTAL_CHAOS_DURATION
          value: '60'