Kustomize Tips: How to Replace Only the Host in Your Ingress Configuration

Learn how to keep your Ingress configuration's http.paths intact while replacing just the host value in Kubernetes using Kustomize!
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This video is based on the question https://stackoverflow.com/q/66568194/ asked by the user 'jmcollin92' ( https://stackoverflow.com/u/1616656/ ) and on the answer https://stackoverflow.com/a/67422492/ provided by the user 'mroma' ( https://stackoverflow.com/u/1476845/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Transforming Your Ingress Configuration with Kustomize

When managing Kubernetes applications, you might encounter situations where you need to tweak your Ingress configuration. One common requirement is to change the host while preserving the existing HTTP paths. If you've found yourself in this boat, don’t worry! You’re not alone. I’ll guide you through how to achieve this using Kustomize.

The Challenge: Replace the Host Value in Ingress

Given an existing Ingress configuration:

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You want to change only the host value, from the-host-value to the.real.hostname, while keeping the other configurations, particularly the HTTP paths, untouched.

The Solution: Using JSON Patch with Kustomize

Instead of creating a new Ingress configuration that overwrites your paths, you can use a JSON patch to specifically replace only the host. Here’s how to do it step-by-step.

Step 1: Update Your kustomization.yaml

You will need to set up your kustomization.yaml to include both your base configuration and your patch. Here’s an example of how this can look:

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Step 2: Create Your Patch File

Now, create a file named ingress-patch.json. This file will contain the necessary JSON patch instructions to update the host value:

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Explanation of the Patch File

op: Stands for "operation". Here, you are performing a "replace" operation.

path: This specifies the exact location within the Ingress object where the operation should be applied. In this case, it is targeting the host in the first rule.

value: This is the new value that will be applied—in this scenario, the.real.hostname.

Building Your Kustomization

Once you have your kustomization.yaml and patch in place, you are ready to build your configuration. Run the following command in your terminal:

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The expected output should retain the existing HTTP paths while updating only the host to the.real.hostname:

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Final Thoughts

By using a JSON patch with Kustomize, you can make precise changes to your Ingress configurations without disrupting other important settings. This method helps maintain clean and manageable configurations across your Kubernetes deployments.

If you have any questions, feel free to ask. Happy Kustomizing!