OpenEBS Target Network Loss Experiment Details

Experiment Metadata

Type	Description	Tested K8s Platform
OpenEBS	Induce network loss into the cStor target/Jiva controller container	GKE, EKS, Konvoy(AWS), Packet(Kubeadm), Minikube, OpenShift(Baremetal)

Note: In this example, we are using nginx as stateful application that stores static pages on a Kubernetes volume.

Prerequisites

Ensure that the Kubernetes Cluster uses Docker runtime
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 openebs-target-network-loss experiment resource is available in the cluster. If not, install from here
The DATA_PERSISTENCE can be enabled by provide the application's info in a configmap volume so that the experiment can perform necessary checks. Currently, LitmusChaos supports data consistency checks only for MySQL and Busybox.
- For MYSQL data persistence check create a configmap as shown below in the application namespace (replace with actual credentials):
```
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: openebs-target-network-loss
data:
  parameters.yml: | 
    dbuser: root
    dbpassword: k8sDem0
    dbname: test
```
- For Busybox data persistence check create a configmap as shown below in the application namespace (replace with actual credentials):
```
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: openebs-target-network-loss
data:
  parameters.yml: | 
    blocksize: 4k
    blockcount: 1024
    testfile: exampleFile
```
Ensure that the chaosServiceAccount used for the experiment has cluster-scope permissions as the experiment may involve carrying out the chaos in the openebs namespace while performing application health checks in its respective namespace.

Entry Criteria

Application pods are healthy before chaos injection
Application writes are successful on OpenEBS PVs

Exit Criteria

Stateful application pods are healthy post chaos injection
OpenEBS Storage target pods are healthy

If the experiment tunable DATA_PERSISTENCE is set to 'enabled':

Application data written prior to chaos is successfully retrieved/read
Database consistency is maintained as per db integrity check utils

Details

This scenario validates the behaviour of stateful applications and OpenEBS data plane upon high latencies/network loss in accessing the storage controller pod
Injects network loss on the specified container in the controller pod by starting a traffic control tc process with netem rules to add egress delays
Network loss is injected via pumba library with command pumba netem delay by passing the relevant network interface, network loss, chaos duration and regex filter for container name
Can test the stateful application's resilience to loss/slow iSCSI connections

Integrations

Network loss is achieved using the pumba chaos library in case of docker runtime. Support for other other runtimes via tc direct invocation of tc will be added soon.
The desired lib image can be configured in the env variable LIB_IMAGE.

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 cluster role permissions to execute the experiment.

Sample Rbac Manifest

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: target-network-loss-sa
  namespace: default
  labels:
    name: target-network-loss-sa
    app.kubernetes.io/part-of: litmus
---
# Source: openebs/templates/clusterrole.yaml
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: target-network-loss-sa
  labels:
    name: target-network-loss-sa
    app.kubernetes.io/part-of: litmus
rules:
- apiGroups: ["","apps","litmuschaos.io","batch","extensions","storage.k8s.io"]
  resources: ["pods","pods/exec","pods/log","events","jobs","configmaps","secrets","services","persistentvolumeclaims","storageclasses","persistentvolumes","chaosexperiments","chaosresults","chaosengines"]
  verbs: ["create","list","get","patch","update","delete"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: target-network-loss-sa
  labels:
    name: target-network-loss-sa
    app.kubernetes.io/part-of: litmus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: target-network-loss-sa
subjects:
- kind: ServiceAccount
  name: target-network-loss-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
Provide the configMaps and secrets in experiments.spec.components.configMaps/secrets, For more info refer Sample ChaosEngine
To understand the values to provided in a ChaosEngine specification, refer ChaosEngine Concepts

Supported Experiment Tunables

Variables	Description	Type	Notes
APP_PVC	The PersistentVolumeClaim used by the stateful application	Mandatory	PVC may use either OpenEBS Jiva/cStor storage class
TC_IMAGE	Image used for traffic control in linux	Optional	default value is `gaiadocker/iproute2`
LIB_IMAGE	chaos library image used to inject the network loss	Optional	Defaults to `gaiaadm/pumba:0.6.5`. Supported: `docker : gaiaadm/pumba:0.6.5`
TOTAL_CHAOS_DURATION	Total duration for which network loss is injected	Optional	Defaults to 120 seconds
DEPLOY_TYPE	Type of Kubernetes resource used by the stateful application	Optional	Defaults to `deployment`. Supported: `deployment`, `statefulset`
NETWORK_PACKET_LOSS_PERCENTAGE	Total percentage for which network loss is injected	Optional	Defaults to 100 (percent)
DATA_PERSISTENCE	Flag to perform data consistency checks on the application	Optional	Default value is disabled (empty/unset). It supports only `mysql` and `busybox`. Ensure configmap with app details are created
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: target-chaos
  namespace: default
spec:
  # 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: target-network-loss-sa
  experiments:
    - name: openebs-target-network-loss
      spec:
        components:
          env:
            - name: TOTAL_CHAOS_DURATION
              value: '120' # in seconds

            - name: TARGET_CONTAINER
              value: 'cstor-istgt'

            - name: APP_PVC
              value: 'demo-nginx-claim'  

            - name: DEPLOY_TYPE
              value: 'deployment'

Create the ChaosEngine Resource

Create the ChaosEngine manifest prepared in the previous step to trigger the Chaos.

kubectl apply -f chaosengine.yml

Watch Chaos progress

View network loss in action by setting up a ping to the storage controller in the OpenEBS namespace
Watch the behaviour of the application pod and the OpenEBS data replica/pool pods by setting up in a watch on the respective namespaces

watch -n 1 kubectl get pods -n <application-namespace>

Check Chaos Experiment Result

Check whether the application is resilient to the target network loss, once the experiment (job) is completed. The ChaosResult resource naming convention is: <ChaosEngine-Name>-<ChaosExperiment-Name>.

kubectl describe chaosresult target-chaos-openebs-target-network-loss -n <application-namespace>

OpenEBS Target Network Loss Demo [TODO]

A sample recording of this experiment execution is provided here.

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