Pod Memory Hog Exec

Introduction¶

This experiment consumes the Memory resources on the application container on specified memory in megabytes.
It simulates conditions where app pods experience Memory spikes either due to expected/undesired processes thereby testing how the overall application stack behaves when this occurs.

Scenario: Stress the Memory

Pod Memory Hog Exec

Uses¶

View the uses of the experiment

Memory usage within containers is subject to various constraints in Kubernetes. If the limits are specified in their spec, exceeding them can cause termination of the container (due to OOMKill of the primary process, often pid 1) - the restart of the container by kubelet, subject to the policy specified. For containers with no limits placed, the memory usage is uninhibited until such time as the Node level OOM Behaviour takes over. In this case, containers on the node can be killed based on their oom_score and the QoS class a given pod belongs to (bestEffort ones are first to be targeted). This eval is extended to all pods running on the node - thereby causing a bigger blast radius.

This experiment launches a stress process within the target container - which can cause either the primary process in the container to be resource constrained in cases where the limits are enforced OR eat up available system memory on the node in cases where the limits are not specified

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-memory-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-memory-hog-exec-sa
  namespace: default
  labels:
    name: pod-memory-hog-exec-sa
    app.kubernetes.io/part-of: litmus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: pod-memory-hog-exec-sa
  namespace: default
  labels:
    name: pod-memory-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-memory-hog-exec-sa
  namespace: default
  labels:
    name: pod-memory-hog-exec-sa
    app.kubernetes.io/part-of: litmus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: pod-memory-hog-exec-sa
subjects:
- kind: ServiceAccount
  name: pod-memory-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
MEMORY_CONSUMPTION	The amount of memory used of hogging a Kubernetes pod (megabytes)	Defaults to 500MB (Up to 2000MB)
TOTAL_CHAOS_DURATION	The time duration for chaos insertion (seconds)	Defaults to 60s
LIB	The chaos lib used to inject the chaos. Available libs are `litmus`	Defaults to `litmus`
TARGET_PODS	Comma separated list of application pod name subjected to pod memory 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
CHAOS_KILL_COMMAND	The command to kill the chaos process	Defaults to `kill $(find /proc -name exe -lname '*/dd' 2>&1 \| grep -v 'Permission denied' \| awk -F/ '{print $(NF-1)}' \| head -n 1)`. Another useful one that generally works (in case the default doesn't) is `kill -9 $(ps afx \| grep "[dd] if=/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
PODS_AFFECTED_PERC	The Percentage of total pods to target	Defaults to 0 (corresponds to 1 replica), provide numeric value only
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.

Memory Consumption¶

It stresses the MEMORY_CONSUMPTION MB memory of the targeted pod for the TOTAL_CHAOS_DURATION duration. The memory consumption limit is 2000MB

Use the following example to tune this:

# memory to be stressed in MB
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-memory-hog-sa
  experiments:
  - name: pod-memory-hog
    spec:
      components:
        env:
        # memory consuption value in MB
        # it is limited to 2000MB
        - name: MEMORY_CONSUMPTION
          value: '500' #in MB
        - name: TOTAL_CHAOS_DURATION
          value: '60'

Chaos Kill Commands¶

It defines the CHAOS_KILL_COMMAND ENV to set the chaos kill command. Default values of CHAOS_KILL_COMMAND command:

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

Use the following example to tune this:

# provide the chaos kill command 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-memory-hog-exec-sa
  experiments:
  - name: pod-memory-hog-exec
    spec:
      components:
        env:
        # command to kill the dd process
        # alternative command: "kill -9 $(ps afx | grep "[dd] if=/dev/zero" | awk '{print $1}' | tr '\n' ' ')"
        - name: CHAOS_KILL_COMMAND
          value: "kill $(find /proc -name exe -lname '*/dd' 2>&1 | grep -v 'Permission denied' | awk -F/ '{print $(NF-1)}' | head -n 1)"
        - name: TOTAL_CHAOS_DURATION
          value: '60'