docs: kustomize component for base url (#2645)

* docs: kustomize component for base url

* Create kustomization.yaml

* Add license

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---------

Co-authored-by: Nim Jayawardena <[email protected]>

Author: aslafy-z

kustomize/components/custom-base-url/README.md

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+# Customize the Base URL for Online Boutique
+
+This component allows you to change the base URL for the Online Boutique application. By default, the application uses the root path ("/") as its base URL. This customization sets the base URL to "/online-boutique" and updates the health check paths accordingly.
+
+## What it does
+
+1. Sets the `BASE_URL` environment variable to "/online-boutique" for the frontend deployment.
+2. Updates the liveness probe path to "/online-boutique/_healthz".
+3. Updates the readiness probe path to "/online-boutique/_healthz".
+
+## How to use
+
+To apply this customization, you can use Kustomize to include this component in your deployment.
+
+From the `kustomize/` folder at the root level of this repository, execute this command:
+
+```bash
+kustomize edit add component components/custom-base-url
+```
+
+This will update the `kustomize/kustomization.yaml` file, which could look similar to:
+
+```yaml
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+- base
+components:
+- components/custom-base-url
+```
+
+## Render and Deploy
+
+You can locally render these manifests by running:
+
+```bash
+kubectl kustomize .
+```
+
+To deploy the customized application, run:
+
+```bash
+kubectl apply -k .
+```
+
+## Customizing the Base URL
+
+If you want to use a different base URL, you can modify the `value` fields in the kustomization.yaml file. Make sure to update all three occurrences:
+
+1. The `BASE_URL` environment variable
+2. The liveness probe path
+3. The readiness probe path
+
+For example, to change the base URL to "/shop", you would modify the values as follows:
+
+```yaml
+value: /shop
+value: /shop/_healthz
+value: /shop/_healthz
+```
+
+Note: After changing the base URL, make sure to update any internal links or references within your application to use the new base URL.

kustomize/components/custom-base-url/kustomization.yaml

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+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+apiVersion: kustomize.config.k8s.io/v1alpha1
+kind: Component
+patches:
+- target:
+    kind: Deployment
+    name: frontend
+  patch: |-
+    - op: add
+      path: /spec/template/spec/containers/0/env/-
+      value:
+        name: BASE_URL
+        value: /online-boutique
+    - op: replace
+      path: /spec/template/spec/containers/0/livenessProbe/httpGet/path
+      value: /online-boutique/_healthz
+    - op: replace
+      path: /spec/template/spec/containers/0/readinessProbe/httpGet/path
+      value: /online-boutique/_healthz