March 11, 2019

1959 words 10 mins read



A powerful testing tool for Kubernetes clusters.

repo name bloomberg/powerfulseal
repo link
language Python
size (curr.) 7159 kB
stars (curr.) 1230
created 2017-12-05
license Apache License 2.0

PowerfulSeal Travis PyPI

PowerfulSeal adds chaos to your Kubernetes clusters, so that you can detect problems in your systems as early as possible. It kills targeted pods and takes VMs up and down.

It follows the Principles of Chaos Engineering, and is inspired by Chaos Monkey. Watch the Seal at KubeCon 2017 Austin.

On the menu


  • works with OpenStack, AWS, Azure, GCP and local machines
  • speaks Kubernetes natively
  • interactive and autonomous, policy-driven mode
  • web interface to interact with PowerfulSeal
  • metric collection and exposition to Prometheus or Datadog
  • minimal setup, easy yaml-based policies
  • easy to extend


PowerfulSeal works in several modes:

  • Interactive mode is designed to allow you to discover your cluster’s components and manually break things to see what happens. It operates on nodes, pods, deployments and namespaces.

  • Autonomous mode reads a policy file, which can contain any number of pod and node scenarios. Each scenario describes a list of matches, filters and actions to execute on your cluster, and will be executed in a loop.

  • Label mode allows you to specify which pods to kill with a small number of options by adding seal/ labels to pods. This is a more imperative alternative to autonomous mode.

  • Demo mode allows you to point the Seal at a cluster and a metrics-server server and let it try to figure out what to kill, based on the resource utilization.


The setup depends on whether you run PowerfulSeal inside or outside of your cluster.

Running inside of the cluster

If you’re running inside of the cluster (for example from the docker image), the setup is pretty easy.

You can see an example of how to do it in ./kubernetes. The setup involves:

  • creating RBAC rules to allow the seal to list, get and delete pods,
  • creating a powerfulseal configmap and deployment
    • your scenarios will live in the configmap
    • if you’d like to use the UI, you’ll probably also need a service and ingress
    • make sure to use --use-pod-delete-instead-of-ssh-kill flag to not need to configure SSH access for killing pods
  • profit!
    • the Seal will self-discover the way to connect to kubernetes and start executing your policy

Running outside of the cluster

If you’re running outside of your cluster, the setup will involve:

  • pointing PowerfulSeal at your Kubernetes cluster by giving it a Kubernetes config file
  • pointing PowerfulSeal at your cloud by specifying the cloud driver to use and providing credentials
  • making sure the seal can SSH into the nodes in order to execute docker kill command
  • writing a set of policies

It should look something like this.

Minikube setup

It is possible to test a subset of Seal’s functionality using a minikube setup.

To achieve that, please inspect the Makefile. You will need to override the ssh host, specify the correct username and use minikube’s ssh keys.

If you’d like to test out the interactive mode, start with this:

seal \
  -vv \
  interactive \
    --no-cloud \
    --inventory-kubernetes \
    --ssh-allow-missing-host-keys \
    --remote-user docker \
    --ssh-path-to-private-key `minikube ssh-key` \
    --ssh-password `minikube ssh-password` \
    --override-ssh-host `minikube ip`

For label mode, try something like this:

seal \
  -vv \
  label \
    --no-cloud \
    --min-seconds-between-runs 3 \
    --max-seconds-between-runs 10 \
    --inventory-kubernetes \
    --ssh-allow-missing-host-keys \
    --remote-user docker \
    --ssh-path-to-private-key `minikube ssh-key` \
    --ssh-password `minikube ssh-password` \
    --override-ssh-host `minikube ip`

For autonomous mode, this should get you started:

seal \
  -vv \
  autonomous \
    --no-cloud \
    --policy-file ./examples/policy_kill_random_default.yml \
    --inventory-kubernetes \
    --prometheus-collector \
    --prometheus-host \
    --prometheus-port 9999 \
    --ssh-allow-missing-host-keys \
    --remote-user docker \
    --ssh-path-to-private-key `minikube ssh-key` \
    --ssh-password `minikube ssh-password` \
    --override-ssh-host `minikube ip` \
    --host \
    --port 30100

Getting started

PowerfulSeal is available to install through pip:

pip install powerfulseal
powerfulseal --help # or seal --help

To start the web interface, use flags --server --server-host [HOST] --server-port [PORT] when starting PowerfulSeal in autonomous mode and visit the web server at http://HOST:PORT/.

Both Python 3.6 and Python 3.7 are supported.


The automatically built docker images are now available on docker hub

docker pull bloomberg/powerfulseal:2.7.0

Modes of operation

Interactive mode

$ seal interactive --help

Make sure you hit tab for autocompletion - that’s what really makes the seal easy to use.

Here’s a sneak peek of what you can do in the interactive mode:

demo nodes

demo pods

Autonomous mode

Autonomous reads the scenarios to execute from the policy file, and runs them:

  1. The matches are combined together and deduplicated to produce an initial working set
  2. They are run through a series of filters
  3. For all the items remaining after the filters, all actions are executed
$ seal autonomous --help

Writing policies

A minimal policy file, doing nothing, looks like this:

  loopsNumber: 1 # will execute the provided scenarios once and then exit

nodeScenarios: []

podScenarios: [] 

A more interesting schema, that kills a random pod in default namespace every 1-30 seconds:

  # we don't set loopsNumber, so it will loop indefinitely
  minSecondsBetweenRuns: 1
  maxSecondsBetweenRuns: 30

nodeScenarios: []
  - name: "delete random pods in default namespace"

      - namespace:
          name: "default"

      - randomSample:
          size: 1

      - kill:
          probability: 0.77
          force: true

A full featured example listing most of the available options can be found in the tests.

The schemas are validated against the powerful JSON schema.

Metrics collection

Autonomous mode also comes with the ability for metrics useful for monitoring to be collected. PowerfulSeal currently has a stdout, Prometheus and Datadog collector. However, metric collectors are easily extensible so it is easy to add your own. More details can be found here.

Web User Interface

:warning: If you’re not going to use the UI, use the flag --headless to disable it

PowerfulSeal comes with a web interface to help you navigate Autonomous Mode. Features include:

  • starting/stopping autonomous mode
  • viewing and filtering logs
  • changing the configuration (either overwriting the remote policy file or copying the changes to clipboard)
  • stopping/killing individual nodes and pods

web interface

Label mode

Label mode is a more imperative alternative to autonomous mode, allowing you to specify which specific per-pod whether a pod should be killed, the days/times it can be killed and the probability of it being killed.

To mark a pod for attack, do kubectl label pods my-app-1 seal/enabled=true, and the Seal will start attacking it, but only during working hours (defaults).

Detailed instructions on how to use label mode can be found in

$ seal label --help

Demo mode

The main way to use PowerfulSeal is to write a policy file for Autonomous mode which reflects realistic failures in your system. However, PowerfulSeal comes with a demo mode to demonstrate how it can cause chaos on your Kubernetes cluster. Demo mode gets all the pods in the cluster, selects those which are using the most resources, then kills them based on a probability.

Demo mode requires metrics-server. To run demo mode, use the demo subcommand along with --metrics-server-path (path to metrics-server without a trailing slash, e.g., http://localhost:8080/api/v1/namespaces/kube-system/services/https:metrics-server:/proxy). You can also optionally specify --aggressiveness (from 1 (weakest) to 5 (strongest)) inclusive, as well as --[min/max]-seconds-between-runs.

$ seal demo --help

Inventory File

PowerfulSeal can use an ansible-style inventory file (in ini format)




Cloud Provider Requirements


In all cases, the SSH Keys must be set up for SSH Client access of the nodes.

Note: With GCP, running gcloud compute config-ssh makes SSHing to node instances easier by adding an alias for each instance to the user SSH configuration (~/.ssh/config) file and then being able to use the generated file with --ssh-path-to-private-key argument.


The credentials to connect to Azure may be specified in one of two ways:

  1. Supply the full path to an Azure credentials file in the environment variable AZURE_AUTH_LOCATION.
    This is the easiest method. The credentials file can be generated via az aks get-credentials -n <cluster name> -g <resource group> -a -f <destination credentials file>
  2. Supply the individual credentials in the environment variables: AZURE_SUBSCRIPTION_ID, AZURE_CLIENT_ID, AZURE_CLIENT_SECRET, AZURE_TENANT_ID


The credentials to connect to AWS are specified the same as for the AWS CLI


The easiest way to use PowerfulSeal, is to download and source the OpenRC file you can get from Horizon. It should ask you for your password, and it should set all the OS_* variables for you. Alternatively, you can set them yourself.

Both approaches are detailed in the official documentation.


Google Cloud SDK and kubectl are required

The GCP cloud driver supports managed (GKE) and custom Kubernetes clusters running on top of Google Cloud Compute.

For setting up PowerfulSeal, the first step is configuring gcloud SDK (as PowerfulSeal will work with your configured project and region) and pointing kubectl to your cluster. Both can be configured easily following this tutorial (For GKE!). In case you don’t want to use the default project/region of gcloud SDK, you can point PowerfulSeal to the correct one (in json) with --gcp-config-file argument.

For being able to run node related commands, credentials have to be specified in one of these ways:

  1. Service account (Recommended): a Google account that is associated with your GCP project, as opposed to a specific user. PowerfulSeal uses the environment variable and is pretty straightforward to set up using this tutorial.
  2. User account: Not recommended as you can reach easily reach a “quota exceeded” or “API not enabled” error. PowerfulSeal uses auto-discovery and to get it working just follow this.

Having configuration ready and ssh connection to the node instances working, you can start playing with PowerfulSeal with this example: powerfulseal interactive --kubeconfig ~/.kube/config --gcp --inventory-kubernetes --ssh-allow-missing-host-keys --ssh-path-to-private-key ~/.ssh/google_compute_engine --remote-user myuser

Note: In case of running inside Pyenv and getting python2 command not found error when running gcloud (and you want to run PowerfulSeal with Python 3+), this might be useful, as gcloud requires Python2.


PowerfulSeal uses tox to test with multiple versions on Python. The recommended setup is to install and locally activate the Python versions under tox.ini with pyenv.

Once the required Python versions are set up and can be discovered by tox (e.g., by having them discoverable in your PATH), you can run the tests by running tox.

For testing the web server and more details on testing, see

Read about the PowerfulSeal


Where can I learn more about Chaos Engineering ?

We found these two links to be a good start:

How is it different from Chaos Monkey ?

PowerfulSeal was inspired by Chaos Monkey, but it differs in a couple of important ways.

The Seal does:

  • speak Kubernetes
  • offer flexible, easy to write YAML scenarios
  • provide interactive mode with awesome tab-completion

The Seal doesn’t:

  • need external dependencies (db, Spinnaker), apart from SSH, cloud and Kubernetes API access
  • need you to setup cron

Can I contribute to The Seal ?

We would love you to. In particular, it would be great to get help with:

Check out our file for more information about how to contribute.

Why a Seal ?

It might have been inspired by this comic.


PowerfulSeal logo Copyright 2018 The Linux Foundation, and distributed under the Creative Commons Attribution (CC-BY-4.0) license.

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