Node memory hog

Node memory hog causes memory resource exhaustion on the Kubernetes node.

• It is injected using a helper pod running the Linux stress-ng tool (a workload generator).
• The chaos affects the application for a specific duration.

Use cases

• Node memory hog fault causes memory resource exhaustion on the Kubernetes node.
• It aims to verify resilience of applications whose replicas may be evicted on account on nodes becoming unschedulable (in NotReady state) due to lack of memory resources.
• It simulates the situation of memory leaks in the deployment of microservices.
• It simulates application slowness due to memory starvation.
• It simulates noisy neighbour problems due to hogging.
• It verifies pod priority and QoS setting for eviction purposes.
• It also verifies application restarts on OOM kills.

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: node-memory-hog
spec:
  definition:
    scope: Cluster
permissions:
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["create", "delete", "get", "list", "patch", "deletecollection", "update"]
  - apiGroups: [""]
    resources: ["events"]
    verbs: ["create", "get", "list", "patch", "update"]
  - apiGroups: [""]
    resources: ["chaosEngines", "chaosExperiments", "chaosResults"]
    verbs: ["create", "delete", "get", "list", "patch", "update"]
  - apiGroups: [""]
    resources: ["pods/log"]
    verbs: ["get", "list", "watch"]
  - apiGroups: [""]
    resources: ["pods/exec"]
    verbs: ["get", "list", "create"]
  - apiGroups: ["batch"]
    resources: ["jobs"]
    verbs: ["create", "delete", "get", "list", "deletecollection"]
  - apiGroups: [""]
    resources: ["nodes"]
    verbs: ["get", "list"]

Prerequisites

• Kubernetes > 1.16
• The target nodes should be in the ready state before and after injecting chaos.

Mandatory tunables

Tunable	Description	Notes
TARGET_NODES	Comma-separated list of nodes subject to node I/O stress.	For example, node-1,node-2. For more information, go to target nodes.
NODE_LABEL	It contains the node label that is used to filter the target nodes.	It is mutually exclusive with the TARGET_NODES environment variable. If both are provided, TARGET_NODES takes precedence. For more information, go to target nodes with labels.

Optional tunables

Tunable	Description	Notes
TOTAL_CHAOS_DURATION	Duration that you specify, through which chaos is injected into the target resource (in seconds).	Default: 120 s. For more information, go to duration of the chaos.
LIB_IMAGE	Image used to run the stress command.	Default: harness/chaos-go-runner:main-latest. For more information, go to image used by the helper pod.
MEMORY_CONSUMPTION_PERCENTAGE	Percent of the total node memory capacity.	Default: 30. For more information, go to memory consumption percentage.
MEMORY_CONSUMPTION_MEBIBYTES	Amount of the total available memory (in mebibytes). It is mutually exclusive with MEMORY_CONSUMPTION_PERCENTAGE.	For example, 256. For more information, go to memory consumption bytes.
NUMBER_OF_WORKERS	Number of VM workers involved in the stress.	Default: 1. For more information, go to workers for stress.
RAMP_TIME	Period to wait before and after injecting chaos (in seconds).	For example, 30 s. For more information, go to ramp time.
NODES_AFFECTED_PERC	Percentage of the total nodes to target. It takes numeric values only.	Default: 0 (corresponds to 1 node). For more information, go to node affected percentage.
SEQUENCE	Sequence of chaos execution for multiple target pods.	Default: parallel. Supports serial sequence as well. For more information, go to sequence of chaos execution.

Memory consumption percentage

Memory consumed (in percentage). Tune it by using the MEMORY_CONSUMPTION_PERCENTAGE environment variable.

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

# 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: litmus-admin
  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

Memory available (in mebibytes). Tune it by using the MEMORY_CONSUMPTION_MEBIBYTES environment variable. It is mutually exclusive with the MEMORY_CONSUMPTION_PERCENTAGE environment variable. If MEMORY_CONSUMPTION_PERCENTAGE environment variable is set, the fault uses this value for the stress.

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

# 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: litmus-admin
  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

Number of workers for stress. Tune it by using the NUMBER_OF_WORKERS environment variable.

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

# provide for the workers count for the stress
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  annotationCheck: "false"
  chaosServiceAccount: litmus-admin
  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'