add harness cd integration tutorial (#32)

Signed-off-by: Neelanjan Manna <neelanjan.manna@harness.io>

tutorials/run-chaos-experiments/integration-with-harness-cd.md

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+---
+sidebar_position: 3
+title: Integration with Harness CD
+description: HCE integration for continuous chaos validation within CD pipelines.
+---
+
+Welcome to this tutorial on HCE integration for Harness CD which allows chaos experiments to be executed as part of a Harness CD pipeline. Before we start, please make sure you have completed the previous tutorials.
+
+## What is Harness CD?
+[Harness CD](https://harness.io/products/continuous-delivery) is a continuous delivery platform for cloud and on-premise projects. It enables DevOps engineers to automate code testing, deployment, and rollbacks. 
+
+The CD pipelines created as part of Harness CD can natively integrate HCE experiments for continuous resiliency validation as well as automated failure mitigation, which we will learn about here.
+
+As part of the tutorial we have a pre-curated CD pipeline for deploying our demo application, Online Boutique Shop, to a Kubernetes cluster from [this](https://github.com/neelanjan00/boutique-app-monitoring) repository. Also, we have defined a pipeline webhook trigger for the repository such that any code change in the `main` branch triggers the CD pipeline to create a new deployment. 
+
+![Deployment Pipeline](./static/integration-with-harness-cd/deployment-pipeline.png)
+
+It can be observed that currently the pipeline is able to deploy the application and we have exactly one replica of each microservice, including the **cart** deployment which we are going to target.
+
+![Online Boutique App Cart](./static/integration-with-harness-cd/online-boutique-app-cart.png)
+
+## Adding a Chaos Step
+
+Now let us add a chaos step to this pipeline so that the chaos experiment we had created in the previous tutorial, `cart-pod-delete`, will run whenever a new pipeline deployment is triggered. This will allow us to validate the deployment against the chaos hypothesis.
+
+To add the chaos step, select the **Add Step** icon next to the **Rollout Deployment** icon for the CD deployment stage.
+
+![Add Chaos Step](./static/integration-with-harness-cd/add-chaos-step.png)
+
+Next, select **Chaos Step** to add it. Now we can configure this step. Name the step as **Boutique Cart Delete**. You can also provide a description, optionally. Next, under **Select Chaos Experiment** dropdown, search and select the **cart-pod-delete** experiment.
+
+![Select Experiment](./static/integration-with-harness-cd/select-experiment.png)
+
+Select **Add to Pipeline**. For expected resiliency score, provide **100**, which means that only mark the step as passed if the resiliency score obtained upon the experiment execution is 100%. 
+
+![Chaos Step Config](./static/integration-with-harness-cd/chaos-step-config.png)
+
+Next, go to the **Advanced** tab. Under **Failure Strategy** select **Add**. For **On failure of type** select **All Errors** and for **Perform Action** select **Rollback Stage**. 
+
+This will ensure that if the chaos experiment's resiliency score is less than 100%, the deployment will be rolled back to the previous version. Hence, the application deployment is continuously validated to be resilient before it gets deployed, otherwise the deployment is safely rolled back to the previous version until the weakness in the application can be mitigated.
+
+![Advanced Chaos Step Config](./static/integration-with-harness-cd/advanced-chaos-step-config.png)
+
+Now, select **Apply Changes**. That's all it takes to add a chaos step to your deployment pipeline. Select **Save** to save the changes to the pipeline.
+
+![Pipeline Updated](./static/integration-with-harness-cd/pipeline-updated.png)
+
+## Executing the CD Pipeline
+
+Now if we manually **Run** this pipeline, we will observe that the pipeline will attempt to deploy the application as part of the CD deployment stage. However, the stage will fail with an error due to the failure of the **Boutique Cart Delete** chaos step, causing the CD to initiate a rollback and revert to the previous healthy deployment.
+
+![CD Pipeline Failed](./static/integration-with-harness-cd/cd-pipeline-failed.png)
+
+At this point we can validate that the application is still accessible, which indicates that the rollback was indeed successful.
+
+A closer inspection indicates that the failure of the chaos step is caused by a resiliency score of only 50%, which is less than the passing criteria of 100%. This can be validated by checking the **cart-pod-delete** experiment under the **Chaos Experiments** page, where the last experiment run has yielded a resiliency score of 50% only.
+
+![Chaos Experiment Failed](./static/integration-with-harness-cd/chaos-experiment-failed.png)
+
+Hence, we were able to verify a potential weakness in our application using the HCE experiment and observed how the Harness CD pipeline integration can benefit from the continuous chaos validation.
+
+Now, let us see how you can resolve this weakness in your application so that it can be successfully deployed. If we update the manifest from which we are deploying the application in the repo (`manifest/app.yaml`) so that the number of pods for the cart deployment is bumped to **2**, we should be able to successfully deploy the application.
+
+As soon as the changes are pushed to the `main` branch of the repo, we can observe that a new pipeline has been triggered, due to the repository webhook that we have defined.
+
+![New Pipeline Triggered](./static/integration-with-harness-cd/new-pipeline-triggered.png)
+
+Upon the completion of the pipeline, we can observe that the deployment is successful with the chaos step obtaining 100% resiliency score. Hence, the experiment has passed and our resilient application is now deployed. We can also validate that the corresponding chaos experiment run has been successful with a 100% resiliency score.
+
+![CD Pipeline Passed](./static/integration-with-harness-cd/cd-pipeline-passed.png)
+
+Congratulations! You have now executed a chaos experiment as part of a Harness CD pipeline where you validated the resiliency of the application in a continuous manner.