Node Memory Hog

Introduction¶

This experiment causes Memory resource exhaustion on the Kubernetes node. The experiment aims to verify resiliency of applications whose replicas may be evicted on account on nodes turning unschedulable (Not Ready) due to lack of Memory resources.
The Memory chaos is injected using a helper pod running the linux stress-ng tool (a workload generator)- The chaos is effected for a period equalling the TOTAL_CHAOS_DURATION and upto MEMORY_CONSUMPTION_PERCENTAGE(out of 100) or MEMORY_CONSUMPTION_MEBIBYTES(in Mebibytes out of total available memory).
Application implies services. Can be reframed as: Tests application resiliency upon replica evictions caused due to lack of Memory resources

Scenario: Stress the memory of node

Node Memory Hog

Uses¶

View the uses of the experiment

coming soon

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 node-memory-hog 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 target nodes should be in ready 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: node-memory-hog-sa
  namespace: default
  labels:
    name: node-memory-hog-sa
    app.kubernetes.io/part-of: litmus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: node-memory-hog-sa
  labels:
    name: node-memory-hog-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"]
  # 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"]
  # for experiment to perform node status checks
  - apiGroups: [""]
    resources: ["nodes"]
    verbs: ["get","list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: node-memory-hog-sa
  labels:
    name: node-memory-hog-sa
    app.kubernetes.io/part-of: litmus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: node-memory-hog-sa
subjects:
- kind: ServiceAccount
  name: node-memory-hog-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

Mandatory Fields

Variables	Description	Notes
TARGET_NODES	Comma separated list of nodes, subjected to node memory hog chaos
NODE_LABEL	It contains node label, which will be used to filter the target nodes if TARGET_NODES ENV is not set	It is mutually exclusive with the TARGET_NODES ENV. If both are provided then it will use the TARGET_NODES

Optional Fields

Variables	Description	Notes
TOTAL_CHAOS_DURATION	The time duration for chaos insertion (in seconds)	Optional	Defaults to 120
LIB	The chaos lib used to inject the chaos	Optional	Defaults to `litmus`
LIB_IMAGE	Image used to run the stress command	Optional	Defaults to `litmuschaos/go-runner:latest`
MEMORY_CONSUMPTION_PERCENTAGE	Percent of the total node memory capacity	Optional	Defaults to 30
MEMORY_CONSUMPTION_MEBIBYTES	The size in Mebibytes of total available memory. When using this we need to keep MEMORY_CONSUMPTION_PERCENTAGE empty as the percentage have more precedence	Optional
NUMBER_OF_WORKERS	It is the number of VM workers involved in IO disk stress	Optional	Default to 1
RAMP_TIME	Period to wait before and after injection of chaos in sec	Optional
NODES_AFFECTED_PERC	The Percentage of total nodes to target	Optional	Defaults to 0 (corresponds to 1 node), provide numeric value only
SEQUENCE	It defines sequence of chaos execution for multiple target pods	Default value: parallel. Supported: serial, parallel

Experiment Examples¶

Common and Node specific tunables¶

Refer the common attributes and Node specific tunable to tune the common tunables for all experiments and node specific tunables.

Memory Consumption Percentage¶

It stresses the MEMORY_CONSUMPTION_PERCENTAGE percentage of total node capacity of the targeted node.

Use the following example to tune this:

# stress the memory of the targeted node with MEMORY_CONSUMPTION_PERCENTAGE of node capacity
# it is mutually exclusive with the MEMORY_CONSUMPTION_MEBIBYTES.
# if both are provided then it will use MEMORY_CONSUMPTION_PERCENTAGE for stress
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  annotationCheck: "false"
  chaosServiceAccount: node-memory-hog-sa
  experiments:
  - name: node-memory-hog
    spec:
      components:
        env:
        # percentage of total node capacity to be stressed
        - name: MEMORY_CONSUMPTION_PERCENTAGE
          value: '10' # in percentage
        - name: TOTAL_CHAOS_DURATION
          value: '60'

Memory Consumption Mebibytes¶

It stresses the MEMORY_CONSUMPTION_MEBIBYTES MiBi of the memory of the targeted node. It is mutually exclusive with the MEMORY_CONSUMPTION_PERCENTAGE ENV. If MEMORY_CONSUMPTION_PERCENTAGE ENV is set then it will use the percentage for the stress otherwise, it will stress the i/o based on MEMORY_CONSUMPTION_MEBIBYTES ENV.

Use the following example to tune this:

# stress the memory of the targeted node with given MEMORY_CONSUMPTION_MEBIBYTES
# it is mutually exclusive with the MEMORY_CONSUMPTION_PERCENTAGE.
# if both are provided then it will use MEMORY_CONSUMPTION_PERCENTAGE for stress
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  annotationCheck: "false"
  chaosServiceAccount: node-memory-hog-sa
  experiments:
  - name: node-memory-hog
    spec:
      components:
        env:
        # node memory to be stressed
        - name: MEMORY_CONSUMPTION_MEBIBYTES
          value: '500' # in MiBi
        - name: TOTAL_CHAOS_DURATION
          value: '60'

Workers For Stress¶

The workers count for the stress can be tuned with NUMBER_OF_WORKERS ENV.

Use the following example to tune this:

# provide for the workers count for the stress
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  annotationCheck: "false"
  chaosServiceAccount: node-memory-hog-sa
  experiments:
  - name: node-memory-hog
    spec:
      components:
        env:
        # total number of workers involved in stress
        - name: NUMBER_OF_WORKERS
          value: '1' 
        - name: TOTAL_CHAOS_DURATION
          value: '60'