Disk Fill Experiment Details
Experiment Metadata
Type | Description | Tested K8s Platform |
---|---|---|
Chaos | Fill up Ephemeral Storage of a Pod | GKE, EKS, AKS |
Prerequisites
- Ensure that Kubernetes Version > 1.13
- 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
disk-fill
experiment resource is available in the cluster by executingkubectl get chaosexperiments
in the desired namespace If not, install from here - Cluster must run docker container runtime
- Appropriate Ephemeral Storage Requests and Limits should be set for the application before running the experiment. An example specification is shown below:
apiVersion: v1
kind: Pod
metadata:
name: frontend
spec:
containers:
- name: db
image: mysql
env:
- name: MYSQL_ROOT_PASSWORD
value: "password"
resources:
requests:
ephemeral-storage: "2Gi"
limits:
ephemeral-storage: "4Gi"
- name: wp
image: wordpress
resources:
requests:
ephemeral-storage: "2Gi"
limits:
ephemeral-storage: "4Gi"
Entry-Criteria
- Application pods are healthy before chaos injection.
Exit-Criteria
- Application pods are healthy post chaos injection.
Details
- Causes Disk Stress by filling up the ephemeral storage of the pod (in the /var/lib/docker/container/{{container_id}}) on any given node.
- Causes the application pod to get evicted if the capacity filled exceeds the pod's ephemeral storage limit.
- Tests the Ephemeral Storage Limits, to ensure those parameters are sufficient.
- Tests the application's resiliency to disk stress/replica evictions.
Integrations
- Disk Fill can be effected using the chaos library:
litmus
, which makes use ofdd
to create a file of specified capacity on the node. - The desired chaoslib can be selected by setting the above options as value for the env variable
LIB
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 create the chaosServiceAccount, 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: disk-fill-sa
namespace: default
labels:
name: disk-fill-sa
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRole
metadata:
name: disk-fill-sa
labels:
name: disk-fill-sa
rules:
- apiGroups: ["","apps","litmuschaos.io","batch"]
resources: ["pods","jobs","pods/exec","events","pods/log","chaosengines","chaosexperiments","chaosresults"]
verbs: ["create","list","get","patch","update","delete"]
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
name: disk-fill-sa
labels:
name: disk-fill-sa
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: ClusterRole
name: disk-fill-sa
subjects:
- kind: ServiceAccount
name: disk-fill-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 |
---|---|---|---|
FILL_PERCENTAGE | Percentage to fill the Ephemeral storage limit | Mandatory | Can be set to more than 100 also, to force evict the pod |
TARGET_CONTAINER | Name of container which is subjected to disk-fill | Mandatory | |
CONTAINER_PATH | Storage Location of containers | Optional | Defaults to '/var/lib/docker/containers' |
TOTAL_CHAOS_DURATION | The time duration for chaos insertion (sec) | Optional | Defaults to 60s |
LIB | The chaos lib used to inject the chaos | Optional | Defaults to `litmus` |
LIB_IMAGE | The image used to fill the disk | Optional | Defaults to `litmuschaos/litmus-go:latest` |
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: disk-fill-sa
monitoring: false
# It can be delete/retain
jobCleanUpPolicy: 'delete'
experiments:
- name: disk-fill
spec:
components:
env:
# specify the fill percentage according to the disk pressure required
- name: FILL_PERCENTAGE
value: '80'
- name: TARGET_CONTAINER
value: 'nginx'
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
View the status of the pods as they are subjected to disk stress.
watch -n 1 kubectl get pods -n <application-namespace>
Monitor the capacity filled up on the host filesystem
watch -n 1 du -kh /var/lib/docker/containers/<container-id>
Abort/Restart the Chaos Experiment
To stop the pod-delete experiment immediately, either delete the ChaosEngine resource or execute the following command:
kubectl patch chaosengine <chaosengine-name> -n <namespace> --type merge --patch '{"spec":{"engineState":"stop"}}'
To restart the experiment, either re-apply the ChaosEngine YAML or execute the following command:
kubectl patch chaosengine <chaosengine-name> -n <namespace> --type merge --patch '{"spec":{"engineState":"active"}}'
Notes:
The abort will stop further fill of the local disk, but doesn't reclaim the used capacity. This is a manual operation as of today. The auto-rollback, i.e., in this case reclaim of currently filled disk-space will be implemented in a future release
However, upon graceful completion of the experiment (i.e.,un-aborted), the space is automatically reclaimed as the chaos impact is reverted.
Check Chaos Experiment Result
Check whether the application is resilient to the container kill, once the experiment (job) is completed. The ChaosResult resource name is derived like this:
<ChaosEngine-Name>-<ChaosExperiment-Name>
.kubectl describe chaosresult nginx-chaos-disk-fill -n <application-namespace>
Disk Fill Experiment Demo
- A sample recording of this experiment execution is provided here.