Project: Litmus (Observability and Analysis / Chaos Engineering)
File: pod-io-stress.md

This experiment causes disk stress on the application pod. The experiment aims to verify the resiliency of applications that share this disk resource for ephemeral or persistent storage purposes !!! tip "Scenario: Stress the IO of the target pod" ??? info "View the uses of the experiment" Disk Pressure or CPU hogs is another very common and frequent scenario we find in kubernetes applications that can result in the eviction of the application replica and impact its delivery. Such scenarios that can still occur despite whatever availability aids K8s provides. These problems are generally referred to as "Noisy Neighbour" problems Stressing the disk with continuous and heavy IO for example can cause degradation in reads written by other microservices that use this shared disk for example modern storage solutions for Kubernetes use the concept of storage pools out of which virtual volumes/devices are carved out. Another issue is the amount of scratch space eaten up on a node which leads to the lack of space for newer containers to get scheduled (kubernetes too gives up by applying an "eviction" taint like "disk-pressure") and causes a wholesale movement of all pods to other nodes ??? info "Verify the prerequisites" Ensure that Kubernetes Version > 1.16 Ensure that the Litmus Chaos Operator is running by executing <code>kubectl get pods</code> in operator namespace (typically, <code>litmus</code>).If not, install from <a href="https://v1-docs.litmuschaos.io/docs/getstarted/#install-litmus">here</a> Ensure that the <code>pod-io-stress</code> experiment resource is available in the cluster by executing <code>kubectl get chaosexperiments</code> in the desired namespace. If not, install from <a href="https://hub.litmuschaos.io/api/chaos/master?file=faults/kubernetes/pod-io-stress/fault.yaml">here</a> ??? info "View the default validations" The application pods should be in running state before and after chaos injection. !!! tip "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 RBAC, which is pre installed in the cluster as part of the agent setup.. ??? note "View the Minimal RBAC permissions" ```yaml apiVersion: v1 kind: ServiceAccount metadata: name: pod-io-stress-sa namespace: default labels: name: pod-io-stress-sa app.kubernetes.io/part-of: litmus apiVersion: rbac.authorization.k8s.io/v1 kind: Role metadata: name: pod-io-stress-sa namespace: default labels: name: pod-io-stress-sa app.kubernetes.io/part-of: litmus rules: apiGroups: [""] resources: ["pods"] verbs: ["create","delete","get","list","patch","update", "deletecollection"] apiGroups: [""] resources: ["events"] verbs: ["create","get","list","patch","update"] apiGroups: [""] resources: ["configmaps"] verbs: ["get","list",] apiGroups: [""] resources: ["pods/log"] verbs: ["get","list","watch"] apiGroups: [""] resources: ["pods/exec"] verbs: ["get","list","create"] apiGroups: ["apps"] resources: ["deployments","statefulsets","replicasets", "daemonsets"] verbs: ["list","get"] apiGroups: ["apps.openshift.io"] resources: ["deploymentconfigs"] verbs: ["list","get"] apiGroups: [""] resources: ["replicationcontrollers"] verbs: ["get","list"] apiGroups:

resources: ["rollouts"] verbs: ["list","get"] apiGroups: ["batch"] resources: ["jobs"] verbs: ["create","list","get","delete","deletecollection"] 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-io-stress-sa namespace: default labels: name: pod-io-stress-sa app.kubernetes.io/part-of: litmus roleRef: apiGroup: rbac.authorization.k8s.io kind: Role name: pod-io-stress-sa subjects: kind: ServiceAccount name: pod-io-stress-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. ??? info "check the experiment tunables" <h2>Optional Fields</h2> <table> <tr> <th> Variables </th> <th> Description </th> <th> Notes </th> </tr> <tr> <td> FILESYSTEMUTILIZATIONPERCENTAGE </td> <td> Specify the size as percentage of free space on the file system </td> <td> Default to 10%</td> </tr> <tr> <td> FILESYSTEMUTILIZATIONBYTES </td> <td> Specify the size in GigaBytes(GB). <code>FILESYSTEMUTILIZATIONPERCENTAGE</code> & <code>FILESYSTEMUTILIZATIONBYTES</code> are mutually exclusive. If both are provided, <code>FILESYSTEMUTILIZATIONPERCENTAGE</code> is prioritized. </td> <td> </td> </tr> <tr> <td> NUMBEROFWORKERS </td> <td> It is the number of IO workers involved in IO disk stress </td> <td> Default to 4 </td> </tr> <tr> <td> TOTALCHAOSDURATION </td> <td> The time duration for chaos (seconds) </td> <td> Default to 120s </td> </tr> <tr> <td> VOLUMEMOUNTPATH </td> <td> Fill the given volume mount path</td> <td> </td> </tr> <tr> <td> LIB </td> <td> The chaos lib used to inject the chaos </td> <td> Default to </code>litmus<code>. Available litmus and pumba. </td> </tr> <tr> <td> LIB_IMAGE </td> <td> Image used to run the stress command </td> <td> Default to <code>litmuschaos/go-runner:latest<code> </td> </tr> <tr> <td> TARGET_PODS </td> <td> Comma separated list of application pod name subjected to pod io stress chaos</td> <td> If not provided, it will select target pods randomly based on provided appLabels</td> </tr> <tr> <td> PODSAFFECTEDPERC </td> <td> The Percentage of total pods to target </td> <td> Defaults to 0 (corresponds to 1 replica), provide numeric value only </td> </tr> <tr> <td> CONTAINER_RUNTIME </td> <td> container runtime interface for the cluster</td> <td> Defaults to containerd, supported values: docker, containerd and crio for litmus and only docker for pumba LIB </td> </tr> <tr> <td> SOCKET_PATH </td> <td> Path of the containerd/crio/docker socket file </td> <td> Defaults to </code>/run/containerd/containerd.sock</code> </td> </tr> <tr> <td> RAMP_TIME </td> <td> Period to wait before and after injection of chaos in sec </td> <td> </td> </tr> <tr> <td> SEQUENCE </td> <td> It defines sequence of chaos execution for multiple target pods </td> <td> Default value: parallel. Supported: serial, parallel </td> </tr> </table> Refer the and to tune the common tunables for all experiments and pod specific

It stresses the `FILESYSTEMUTILIZATIONPERCENTAGE` percentage of total free space available in the pod. Use the following example to tune this: ```yaml 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-io-stress-sa experiments: name: pod-io-stress spec: components: env: name: FILESYSTEMUTILIZATIONPERCENTAGE value: '10' #in GB name: TOTALCHAOSDURATION value: '60' ``` It stresses the `FILESYSTEMUTILIZATIONBYTES` GB of the i/o of the targeted pod. It is mutually exclusive with the `FILESYSTEMUTILIZATIONPERCENTAGE` ENV. If `FILESYSTEMUTILIZATIONPERCENTAGE` ENV is set then it will use the percentage for the stress otherwise, it will stress the i/o based on `FILESYSTEMUTILIZATIONBYTES` ENV. Use the following example to tune this: ```yaml 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-io-stress-sa experiments: name: pod-io-stress spec: components: env: name: FILESYSTEMUTILIZATIONBYTES value: '1' #in GB name: TOTALCHAOSDURATION value: '60' ``` It defines the `CONTAINERRUNTIME` and `SOCKETPATH` ENV to set the container runtime and socket file path. `CONTAINER_RUNTIME`: It supports `docker`, `containerd`, and `crio` runtimes. The default value is `docker`. `SOCKET_PATH`: It contains path of docker socket file by default(`/run/containerd/containerd.sock`). For other runtimes provide the appropriate path. Use the following example to tune this: ```yaml 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-io-stress-sa experiments: name: pod-io-stress spec: components: env: name: CONTAINER_RUNTIME value: 'containerd' name: SOCKET_PATH value: '/run/containerd/containerd.sock' name: TOTALCHAOSDURATION value: '60' ``` The volume mount path, which needs to be filled. It can be tuned with `VOLUMEMOUNTPATH` ENV. Use the following example to tune this: ```yaml 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-io-stress-sa experiments: name: pod-io-stress spec: components: env: name: VOLUMEMOUNTPATH value: '/some-dir-in-container' name: TOTALCHAOSDURATION value: '60' ``` The worker's count for the stress can be tuned with `NUMBEROFWORKERS` ENV. Use the following example to tune this: ```yaml 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-io-stress-sa experiments: name: pod-io-stress spec: components: env: name: NUMBEROFWORKERS value: '4' name: TOTALCHAOSDURATION value: '60' ``` It specifies the Pumba chaos library for the chaos injection. It can be tuned via `LIB` ENV. The defaults chaos library is `litmus`. Use the following example to tune this: ```yaml 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-io-stress-sa experiments: name: pod-io-stress spec: components: env: name: LIB value: 'pumba' name: TOTALCHAOSDURATION value: '60' ```