PVC Scenario

Scenario to fill up a given PersistenVolumeClaim by creating a temp file on the PVC from a pod associated with it. The purpose of this scenario is to fill up a volume to understand faults caused by the application using this volume.

How to Run PVC Scenarios

Choose your preferred method to run PVC scenarios:

Example scenario file: pvc_scenario.yaml

Sample scenario config

pvc_scenario:
  pvc_name: <pvc_name>          # Name of the target PVC.
  pod_name: <pod_name>          # Name of the pod where the PVC is mounted. It will be ignored if the pvc_name is defined.
  namespace: <namespace_name>   # Namespace where the PVC is.
  fill_percentage: 50           # Target percentage to fill up the cluster. Value must be higher than current percentage. Valid values are between 0 and 99.
  duration: 60                  # Duration in seconds for the fault.

Steps

Get the pod name where the PVC is mounted.
Get the volume name mounted in the container pod.
Get the container name where the PVC is mounted.
Get the mount path where the PVC is mounted in the pod.
Get the PVC capacity and current used capacity.
Calculate file size to fill the PVC to the target fill_percentage.
Connect to the pod.
Create a temp file kraken.tmp with random data on the mount path:
- dd bs=1024 count=$file_size </dev/urandom > /mount_path/kraken.tmp
Wait for the duration time.
Remove the temp file created:
- rm kraken.tmp

How to Use Plugin Name

Add the plugin name to the list of chaos_scenarios section in the config/config.yaml file

kraken:
    kubeconfig_path: ~/.kube/config                     # Path to kubeconfig
    ..
    chaos_scenarios:
        - pvc_scenarios:
            - scenarios/<scenario_name>.yaml

Note

You can specify multiple scenario files of the same type by adding additional paths to the list:

kraken:
    chaos_scenarios:
        - pvc_scenarios:
            - scenarios/pvc-fill-1.yaml
            - scenarios/pvc-fill-2.yaml
            - scenarios/pvc-fill-3.yaml

You can also combine multiple different scenario types in the same config.yaml file. Scenario types can be specified in any order, and you can include the same scenario type multiple times:

kraken:
    chaos_scenarios:
        - pvc_scenarios:
            - scenarios/pvc-fill.yaml
        - pod_disruption_scenarios:
            - scenarios/pod-kill.yaml
        - container_scenarios:
            - scenarios/container-kill.yaml
        - pvc_scenarios:  # Same type can appear multiple times
            - scenarios/pvc-fill-2.yaml

Run

python run_kraken.py --config config/config.yaml

This scenario fills up a given PersistenVolumeClaim by creating a temp file on the PVC from a pod associated with it. The purpose of this scenario is to fill up a volume to understand faults cause by the application using this volume. For more information refer the following documentation.

Run

If enabling Cerberus to monitor the cluster and pass/fail the scenario post chaos, refer docs. Make sure to start it before injecting the chaos and set CERBERUS_ENABLED environment variable for the chaos injection container to autoconnect.

$ podman run \
  --name=<container_name> \
  --net=host \
  --pull=always \
  --env-host=true \
  -v <path-to-kube-config>:/home/krkn/.kube/config:Z \
  -d containers.krkn-chaos.dev/krkn-chaos/krkn-hub:pvc-scenarios
$ podman logs -f <container_name or container_id> # Streams Kraken logs
$ podman inspect <container-name or container-id> \
  --format "{{.State.ExitCode}}" # Outputs exit code which can considered as pass/fail for the scenario

Note

–env-host: This option is not available with the remote Podman client, including Mac and Windows (excluding WSL2) machines. Without the –env-host option you’ll have to set each environment variable on the podman command line like -e <VARIABLE>=<value>

$ docker run $(./get_docker_params.sh) \
  --name=<container_name> \
  --net=host \
  --pull=always \
  -v <path-to-kube-config>:/home/krkn/.kube/config:Z \
  -d containers.krkn-chaos.dev/krkn-chaos/krkn-hub:pvc-scenarios
$ docker run \
  -e <VARIABLE>=<value> \
  --name=<container_name> \
  --net=host \
  --pull=always \
  -v <path-to-kube-config>:/home/krkn/.kube/config:Z \
  -d containers.krkn-chaos.dev/krkn-chaos/krkn-hub:pvc-scenarios

$ docker logs -f <container_name or container_id> # Streams Kraken logs
$ docker inspect <container-name or container-id> \
  --format "{{.State.ExitCode}}" # Outputs exit code which can considered as pass/fail for the scenario

Tip

Because the container runs with a non-root user, ensure the kube config is globally readable before mounting it in the container. You can achieve this with the following commands:

kubectl config view --flatten > ~/kubeconfig && chmod 444 ~/kubeconfig && docker run $(./get_docker_params.sh) --name=<container_name> --net=host --pull=always -v ~/kubeconfig:/home/krkn/.kube/config:Z -d containers.krkn-chaos.dev/krkn-chaos/krkn-hub:<scenario>

Supported parameters

The following environment variables can be set on the host running the container to tweak the scenario/faults being injected:

Example if –env-host is used:

export <parameter_name>=<value>

OR on the command line like example:

-e <VARIABLE>=<value>

If both PVC_NAME and POD_NAME are defined, POD_NAME value will be overridden from the Mounted By: value on PVC definition.

See list of variables that apply to all scenarios here that can be used/set in addition to these scenario specific variables

Parameter	Description	Type	Default
PVC_NAME	Targeted PersistentVolumeClaim in the cluster (if null, POD_NAME is required)	string
POD_NAME	Targeted pod in the cluster (if null, PVC_NAME is required)	string
NAMESPACE	Targeted namespace in the cluster (required)	string
FILL_PERCENTAGE	Targeted percentage to be filled up in the PVC	number	50
DURATION	Duration in seconds with the PVC filled up	number	60
BLOCK_SIZE	Block size in bytes for the dd command used to fill the PVC	number	102400

Note

In case of using custom metrics profile or alerts profile when CAPTURE_METRICS or ENABLE_ALERTS is enabled, mount the metrics profile from the host on which the container is run using podman/docker under /home/krkn/kraken/config/metrics-aggregated.yaml and /home/krkn/kraken/config/alerts.

For example:

$ podman run \
  --name=<container_name> \
  --net=host \
  --pull=always \
  --env-host=true \
  -v <path-to-custom-metrics-profile>:/home/krkn/kraken/config/metrics-aggregated.yaml \
  -v <path-to-custom-alerts-profile>:/home/krkn/kraken/config/alerts \
  -v <path-to-kube-config>:/home/krkn/.kube/config:Z \
  -d containers.krkn-chaos.dev/krkn-chaos/krkn-hub:pvc-scenarios

krknctl run pvc-scenarios [--<parameter> <value>]

Can also set any global variable listed here

Scenario specific parameters:

Parameter	Description	Type	Required	Default
`--pvc-name`	Targeted PersistentVolumeClaim in the cluster (if null, POD_NAME is required)	string	No
`--pod-name`	Targeted pod in the cluster (if null, PVC_NAME is required)	string	No
`--namespace`	Targeted namespace in the cluster (required)	string	Yes
`--fill-percentage`	Targeted percentage to be filled up in the PVC	number	No	50
`--duration`	Duration in seconds with the PVC filled up	number	No	60

Parameter Dependencies

--pvc-name vs --pod-name: At least one is required. If both are set, --pvc-name takes precedence and --pod-name is ignored.

Behavior Notes

Automatic cleanup: After --duration expires, krkn automatically deletes the temporary fill file from the PVC.
PVC requirements: The target PVC must be in Bound state and mounted to an active pod. The scenario locates the mount path by inspecting the pod’s volume mounts.

To see all available scenario options

krknctl run pvc-scenarios --help