Node Taint Experiment Details
Experiment Metadata
Type | Description | Tested K8s Platform |
---|---|---|
Generic | Taint the node where application pod is scheduled. | GKE, AWS, Packet(Kubeadm), Konvoy(AWS), EKS, AKS |
Prerequisites
Ensure that the Litmus Chaos Operator is running by executing
kubectl get pods
in operator namespace (typically,litmus
). If not, install from hereEnsure that the
node-taint
experiment resource is available in the cluster by executingkubectl get chaosexperiments
in the desired namespace. If not, install from hereEnsure that the node specified in the experiment ENV variable
APP_NODE
(the node which will be tainted) should be cordoned before execution of the chaos experiment (before applying the chaosengine manifest) to ensure that the litmus experiment runner pods are not scheduled on it / subjected to eviction. This can be achieved with the following steps:- Get node names against the applications pods:
kubectl get pods -o wide
- Cordon the node
kubectl cordon <nodename>
- Get node names against the applications pods:
Entry Criteria
- Application pods are healthy on the respective Nodes before chaos injection
Exit Criteria
- Target nodes are in Ready state post chaos injection
- Application pods are healthy on the respective Nodes after chaos injection
Details
- This experiment taint the node where application pod is running and verifies if it is scheduled on another available node.
- In the end of experiment it remove the taints from the specified node so that it can be utilised in future.
- After experiment ends, you may manually uncordon the specified node so that it can be utilised in future.
Integrations
- Taint node can be effected using the chaos library:
litmus
- The desired chaos library can be selected by setting
litmus
as value for the env variableLIB
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 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: node-taint-sa
namespace: default
labels:
name: node-taint-sa
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRole
metadata:
name: node-taint-sa
labels:
name: node-taint-sa
rules:
- apiGroups: ["","litmuschaos.io","batch","extensions"]
resources: ["pods","jobs","events","chaosengines","pods/log","daemonsets","pods/eviction","chaosexperiments","chaosresults"]
verbs: ["create","list","get","patch","update","delete"]
- apiGroups: [""]
resources: ["nodes"]
verbs: ["patch","get","list","update"]
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
name: node-taint-sa
labels:
name: node-taint-sa
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: ClusterRole
name: node-taint-sa
subjects:
- kind: ServiceAccount
name: node-taint-sa
namespace: default
Prepare ChaosEngine
- Provide the application info in
spec.appinfo
- Provide the auxiliary applications info (ns & labels) in
spec.auxiliaryAppInfo
- 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 | Specify In ChaosEngine | Notes |
---|---|---|---|
APP_NODE | Name of the node to be tainted | Mandatory | |
TAINT_LABEL | Label and effect to be tainted on application node | Mandatory | |
TOTAL_CHAOS_DURATION | The time duration for chaos insertion (seconds) | Optional | Defaults to 60s |
LIB | The chaos lib used to inject the chaos | Optional | Defaults to `litmus` |
RAMP_TIME | Period to wait before injection of chaos in sec | Optional | |
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 true/false
annotationCheck: 'false'
# It can be active/stop
engineState: 'active'
#ex. values: ns1:name=percona,ns2:run=nginx
auxiliaryAppInfo: ''
appinfo:
appns: 'default'
applabel: 'app=nginx'
appkind: 'deployment'
chaosServiceAccount: node-taint-sa
monitoring: false
# It can be delete/retain
jobCleanUpPolicy: 'delete'
experiments:
- name: node-taint
spec:
components:
env:
# set node name
- name: APP_NODE
value: 'node-1'
# set taint label & effect
# key=value:effect or key:effect
- name: TAINTS
value: 'node.kubernetes.io/unreachable:NoExecute'
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 originally scheduled on the affected node and verify whether they are rescheduled on the other nodes in the Kubernetes Cluster.
watch kubectl get pods,nodes --all-namespaces
Check Chaos Experiment Result
Check whether the application is resilient to the node taint, once the experiment (job) is completed. The ChaosResult resource name is derived like this:
<ChaosEngine-Name>-<ChaosExperiment-Name>
.kubectl describe chaosresult nginx-chaos-node-taint -n <application-namespace>
Post Chaos Steps
In the beginning of experiment, we cordon the node so that chaos-pod won't schedule on the same node (to which we are going to taint) because for some taint with
NoExecute
effect the pods may get scheduled to other nodes(restarted). After experiment ends you can manually uncordon the application node so that it can be utilised in future.kubectl uncordon <node-name>
Node Taint Experiment Demo [TODO]
- A sample recording of this experiment execution is provided here.