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‎README.md‎

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# Kubectl Plugin to Add Support for Environment Variable Evaluation in Kustomize
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This plugin is a `kubectl` plugin that adds support for evaluating environment variables in Kustomize overlays.
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![image](docs/envkustomize.png)
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## Why This Plugin?
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I've used Kustomize extensively over the years, and I've always missed the ability to evaluate environment variables in overlays. The recommended approach, using patches and overlays, is just too much work when managing a large fleet of clusters. It can be a pain even for basic tasks like patching an image name!
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This plugin is largely a response to the frustrations described here:
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* [ConfigMapGenerator should not load values from the build environment](https://github.com/kubernetes-sigs/kustomize/issues/4731)
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* [Reddit discussion on passing dynamic values to Kustomize](https://www.reddit.com/r/kubernetes/comments/116hze5/how_to_pass_dynamic_values_to_kustomize/)
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* [ArgoCD issue on dynamic values](https://github.com/argoproj/argo-cd/issues/1705)
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## How Does It Work?
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The plugin is a lightweight wrapper around the official Kustomize API (krusty) [Kustomizer](https://github.com/kubernetes-sigs/kustomize/blob/master/api/krusty/kustomizer.go). It replaces the original filesystem loader with a custom one that evaluates environment variables before loading the file.
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## How to Use It?
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```bash
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# You need to run it in a valid Kustomize overlay folder like this:
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cd examples
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kubectl envkustomize render
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# Check the rendered.yaml file generated in the same folder
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```
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### Evaluations Supported
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* Basic environment variables replacement: `${{{ VAR }}}`
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* Load of environment variables from `.env` files or from the environment itself (using a prefix to avoid loading all environment variables and to avoid conflicts)
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* Load secrets from GCP Secret Manager (Welcome PRs to add AWS Secrets Manager and Azure Key Vault support)
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* Expand environment with `${{{env-expand://ENV_}}}` to inject automatically all environment variables starting with `ENV_`
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* Support for environment variables substitution even inside helm charts (or other external resources as long as they are referenced in the kustomize overlay)

‎cmd/render.go‎

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package cmd
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import "github.com/spf13/cobra"
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import "kubectl-envkustomize/pkg"
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var renderCmd = &cobra.Command{
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Use: "render",
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Short: "Render kustomize manifests",
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Long: `Render kustomize manifests from the environment configurations. To run this command you meed an .env and kustomization.yaml file on the current directory.`,
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Run: func(cmd *cobra.Command, args []string) {
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envFile, _ := cmd.Flags().GetString("env-file")
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pkg.RenderCmd(envFile)
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},
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}
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func init() {
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renderCmd.Flags().StringP("env-file", "e", ".env", "Path to the environment file")
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}

‎cmd/root.go‎

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package cmd
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import "github.com/spf13/cobra"
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var rootCmd = &cobra.Command{
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Use: "kubectl-envkustomize",
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Short: "Kubectl env kustomize plugin",
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Long: `Kustomize with env support`,
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}
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func Execute() error {
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return rootCmd.Execute()
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}
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func init() {
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rootCmd.AddCommand(renderCmd)
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}

‎docs/envkustomize.png‎

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‎examples/configmap.yaml‎

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# example to make envoy serve a static file
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apiVersion: v1
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kind: ConfigMap
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metadata:
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name: envoy-config
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data:
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envoy.yaml: |
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static_resources:
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listeners:
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- name: listener_0
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address:
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socket_address:
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address: 0.0.0.0
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port_value: 8080
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filter_chains:
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- filters:
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- name: envoy.filters.network.http_connection_manager
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typed_config:
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"@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
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stat_prefix: ingress_http
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route_config:
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name: local_route
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virtual_hosts:
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- name: local_service
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domains: ["*"]
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routes:
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- match:
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prefix: "/"
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direct_response:
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status: 200
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body:
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filename: /etc/envoy/static-file.html
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http_filters:
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- name: envoy.filters.http.router
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static-file.html: |
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<html>
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<body>
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<h1> ${{{ ENV_KUBECTL_WELCOME_TEXT }}} </h1>
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<p>This is a static file served by Envoy.</p>
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</body>
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</html>

‎examples/deploy.yaml‎

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apiVersion: apps/v1
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kind: Deployment
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metadata:
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name: envoy-deployment
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spec:
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replicas: 1
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selector:
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matchLabels:
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app: envoy
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template:
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metadata:
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labels:
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app: envoy
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spec:
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containers:
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- name: envoy
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image: ${{{ ENV_KUBECTL_ENVOY_IMAGE }}} # Example injecting environment variables dynamically
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ports:
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- containerPort: 8080
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volumeMounts:
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- name: envoy-config
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mountPath: /etc/envoy/envoy.yaml
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subPath: envoy.yaml
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- name: static-file
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mountPath: /etc/envoy/static-file.html
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subPath: static-file.html
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# Example setting resources dynamically from environment variables
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resources:
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requests:
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memory: "${{{ ENV_KUBECTL_MEMORY_REQUEST }}}"
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cpu: "${{{ ENV_KUBECTL_CPU_REQUEST }}}"
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limits:
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memory: "${{{ ENV_KUBECTL_CPU_LIMIT }}}"
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cpu: "${{{ ENV_KUBECTL_CPU_LIMIT }}}"
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env:
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# Example injecting environment variables dynamically
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- name: ENVOY_LOG_LEVEL
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value: ${{{ ENV_KUBECTL_ENVOY_LOG_LEVEL }}}
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# Example injecting ALL environment variables with a prefix dynamically
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# check the rendered.yaml to see the result!
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- name: ${{{env-expand://ENV_KUBECTL_ENVOY}}}
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value: ${{{env-expand://ENV_KUBECTL_ENVOY}}}
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volumes:
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- name: envoy-config
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configMap:
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name: envoy-config
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items:
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- key: envoy.yaml
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path: envoy.yaml
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- name: static-file
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configMap:
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name: envoy-config
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items:
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- key: static-file.html
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path: static-file.html
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---
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apiVersion: v1
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kind: Service
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metadata:
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name: envoy-service
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spec:
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selector:
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app: envoy
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ports:
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- protocol: TCP
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port: 80
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targetPort: 8080

‎examples/kustomization.yaml‎

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apiVersion: kustomize.config.k8s.io/v1beta1
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kind: Kustomization
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namespace: test-namespace
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resources:
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- deploy.yaml
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- configmap.yaml
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- pull-image-secret.yaml

‎examples/pull-image-secret.yaml‎

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# Example rendering secrets using environment variables
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apiVersion: v1
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data:
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.dockerconfigjson: ${{{ ENV_KUBECTL_SECRET_DOCKERCONFIGJSON }}}
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kind: Secret
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metadata:
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name: secret-dockerconfigjson
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type: kubernetes.io/dockerconfigjson

‎examples/rendered.yaml‎

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apiVersion: apps/v1
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kind: Deployment
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metadata:
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name: envoy-deployment
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namespace: test-namespace
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spec:
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replicas: 1
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selector:
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matchLabels:
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app: envoy
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template:
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metadata:
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labels:
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app: envoy
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spec:
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containers:
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- env:
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- name: ENVOY_LOG_LEVEL
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value: debug
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- name: ENV_KUBECTL_ENVOY_IMAGE
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value: envoyproxy/envoy:v1.24.0
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- name: ENV_KUBECTL_ENVOY_LOG_LEVEL
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value: debug
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- name: ENV_KUBECTL_ENVOY_TEST1
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value: value1
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- name: ENV_KUBECTL_ENVOY_TEST2
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value: value2
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- name: ENV_KUBECTL_ENVOY_TEST3
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value: value3
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image: envoyproxy/envoy:v1.24.0
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name: envoy
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ports:
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- containerPort: 8080
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resources:
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limits:
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cpu: 250m
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memory: 250m
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requests:
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cpu: 100m
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memory: 128Mi
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volumeMounts:
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- mountPath: /etc/envoy/envoy.yaml
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name: envoy-config
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subPath: envoy.yaml
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- mountPath: /etc/envoy/static-file.html
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name: static-file
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subPath: static-file.html
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volumes:
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- configMap:
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items:
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- key: envoy.yaml
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path: envoy.yaml
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name: envoy-config
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name: envoy-config
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- configMap:
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items:
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- key: static-file.html
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path: static-file.html
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name: envoy-config
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name: static-file
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---
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apiVersion: v1
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kind: Service
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metadata:
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name: envoy-service
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namespace: test-namespace
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spec:
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ports:
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- port: 80
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protocol: TCP
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targetPort: 8080
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selector:
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app: envoy
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---
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apiVersion: v1
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data:
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envoy.yaml: |
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static_resources:
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listeners:
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- name: listener_0
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address:
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socket_address:
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address: 0.0.0.0
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port_value: 8080
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filter_chains:
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- filters:
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- name: envoy.filters.network.http_connection_manager
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typed_config:
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"@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
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stat_prefix: ingress_http
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route_config:
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name: local_route
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virtual_hosts:
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- name: local_service
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domains: ["*"]
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routes:
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- match:
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prefix: "/"
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direct_response:
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status: 200
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body:
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filename: /etc/envoy/static-file.html
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http_filters:
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- name: envoy.filters.http.router
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static-file.html: |
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<html>
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<body>
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<h1> Welcome to env kubectl </h1>
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<p>This is a static file served by Envoy.</p>
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</body>
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</html>
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kind: ConfigMap
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metadata:
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name: envoy-config
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namespace: test-namespace
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---
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apiVersion: v1
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data:
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.dockerconfigjson: bXkgc2VjcmV0
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kind: Secret
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metadata:
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name: secret-dockerconfigjson
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namespace: test-namespace
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type: kubernetes.io/dockerconfigjson
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---

‎go.mod‎

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module kubectl-envkustomize
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go 1.22.4
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require (
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cloud.google.com/go/auth v0.7.2 // indirect
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cloud.google.com/go/auth/oauth2adapt v0.2.3 // indirect
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cloud.google.com/go/compute/metadata v0.5.0 // indirect
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cloud.google.com/go/iam v1.1.11 // indirect
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cloud.google.com/go/secretmanager v1.13.4 // indirect
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github.com/blang/semver/v4 v4.0.0 // indirect
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github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
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github.com/felixge/httpsnoop v1.0.4 // indirect
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github.com/go-errors/errors v1.4.2 // indirect
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github.com/go-logr/logr v1.4.2 // indirect
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github.com/go-logr/stdr v1.2.2 // indirect
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github.com/go-openapi/jsonpointer v0.19.6 // indirect
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github.com/go-openapi/jsonreference v0.20.2 // indirect
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github.com/go-openapi/swag v0.22.4 // indirect
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github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
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github.com/golang/protobuf v1.5.4 // indirect
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github.com/google/gnostic-models v0.6.8 // indirect
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github.com/google/s2a-go v0.1.8 // indirect
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github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510 // indirect
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github.com/googleapis/enterprise-certificate-proxy v0.3.2 // indirect
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github.com/googleapis/gax-go/v2 v2.13.0 // indirect
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github.com/inconshreveable/mousetrap v1.1.0 // indirect
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github.com/josharian/intern v1.0.0 // indirect
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github.com/mailru/easyjson v0.7.7 // indirect
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github.com/monochromegane/go-gitignore v0.0.0-20200626010858-205db1a8cc00 // indirect
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github.com/pkg/errors v0.9.1 // indirect
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github.com/spf13/cobra v1.8.1 // indirect
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github.com/spf13/pflag v1.0.5 // indirect
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github.com/xlab/treeprint v1.2.0 // indirect
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go.opencensus.io v0.24.0 // indirect
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go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.53.0 // indirect
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go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.53.0 // indirect
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go.opentelemetry.io/otel v1.28.0 // indirect
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go.opentelemetry.io/otel/metric v1.28.0 // indirect
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go.opentelemetry.io/otel/trace v1.28.0 // indirect
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go.starlark.net v0.0.0-20200306205701-8dd3e2ee1dd5 // indirect
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golang.org/x/crypto v0.25.0 // indirect
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golang.org/x/net v0.27.0 // indirect
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golang.org/x/oauth2 v0.21.0 // indirect
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golang.org/x/sync v0.7.0 // indirect
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golang.org/x/sys v0.22.0 // indirect
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golang.org/x/text v0.16.0 // indirect
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golang.org/x/time v0.5.0 // indirect
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google.golang.org/api v0.189.0 // indirect
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google.golang.org/genproto v0.0.0-20240722135656-d784300faade // indirect
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google.golang.org/genproto/googleapis/api v0.0.0-20240722135656-d784300faade // indirect
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google.golang.org/genproto/googleapis/rpc v0.0.0-20240722135656-d784300faade // indirect
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google.golang.org/grpc v1.65.0 // indirect
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google.golang.org/protobuf v1.34.2 // indirect
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gopkg.in/evanphx/json-patch.v4 v4.12.0 // indirect
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gopkg.in/yaml.v3 v3.0.1 // indirect
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k8s.io/kube-openapi v0.0.0-20231010175941-2dd684a91f00 // indirect
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sigs.k8s.io/kustomize/api v0.17.3 // indirect
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sigs.k8s.io/kustomize/kyaml v0.17.2 // indirect
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sigs.k8s.io/yaml v1.4.0 // indirect
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)

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