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IO Hog Scenario

The purpose of this scenario is to create disk pressure on a particular node of the Kubernetes/OpenShift cluster for a time span. The scenario allows to attach a node path to the pod as a hostPath volume.

1 - IO Hog Scenarios using Krkn

To enable this plugin add the pointer to the scenario input file scenarios/kube/io-hog.yaml as described in the Usage section.

io-hog options

In addition to the common hog scenario options, you can specify the below options in your scenario configuration to target specific pod IO

OptionTypeDescription
io-block-sizestringthe block size written by the stressor
io-write-bytesstringthe total amount of data that will be written by the stressor. The size can be specified as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g
io-target-pod-folderstringthe folder where the volume will be mounted in the pod
io-target-pod-volumedictionarythe pod volume definition that will be stressed by the scenario.

[!CAUTION] Modifying the structure of io-target-pod-volume might alter how the hog operates, potentially rendering it ineffective.

Usage

To enable hog scenarios edit the kraken config file, go to the section kraken -> chaos_scenarios of the yaml structure and add a new element to the list named hog_scenarios then add the desired scenario pointing to the hog.yaml file.

kraken:
    ...
    chaos_scenarios:
        - hog_scenarios:
            - scenarios/kube/io-hog.yml

2 - IO Hog Scenario using Krkn-Hub

This scenario hogs the IO on the specified node on a Kubernetes/OpenShift cluster for a specified duration. 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 --env-host=true -v <path-to-kube-config>:/root/.kube/config:Z -d quay.io/krkn-chaos/krkn-hub:node-io-hog
$ 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

$ docker run $(./get_docker_params.sh) --name=<container_name> --net=host -v <path-to-kube-config>:/root/.kube/config:Z -d quay.io/krkn-chaos/krkn-hub:node-io-hog
OR 
$ docker run -e <VARIABLE>=<value> --net=host -v <path-to-kube-config>:/root/.kube/config:Z -d quay.io/krkn-chaos/krkn-hub:node-io-hog

$ 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

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>

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

ParameterDescriptionDefault
TOTAL_CHAOS_DURATIONSet chaos duration (in sec) as desired180
IO_BLOCK_SIZEstring size of each write in bytes. Size can be from 1 byte to 4m1m
IO_WORKERSNumber of stressorts5
IO_WRITE_BYTESstring writes N bytes for each hdd process. The size can be expressed as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g10m
NAMESPACENamespace where the scenario container will be deployeddefault
NODE_SELECTORdefines the node selector for choosing target nodes. If not specified, one schedulable node in the cluster will be chosen at random. If multiple nodes match the selector, all of them will be subjected to stress. If number-of-nodes is specified, that many nodes will be randomly selected from those identified by the selector.""
NODE_MOUNT_PATHthe local path in the node that will be mounted in the pod and that will be filled by the scenario""
NUMBER_OF_NODESrestricts the number of selected nodes by the selector""
IMAGEthe container image of the stress workloadquay.io/krkn-chaos/krkn-hog

For example:

$ podman run --name=<container_name> --net=host --env-host=true -v <path-to-custom-metrics-profile>:/root/kraken/config/metrics-aggregated.yaml -v <path-to-custom-alerts-profile>:/root/kraken/config/alerts -v <path-to-kube-config>:/root/.kube/config:Z -d quay.io/krkn-chaos/krkn-hub:node-io-hog