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PodConfigMapController

A custom Kubernetes controller written in Go that watches for Pod events and automatically creates or deletes ConfigMaps containing their metadata. The controller supports:

  • Pod Events: Handles create, update, and delete events for Pods.
  • ConfigMap Management: Creates and deletes ConfigMaps corresponding to Pods.
  • Custom Resource Definition (CRD): Integrates a CRD for dynamic behavior customization.
  • Leader Election: Ensures only one active controller instance operates at a time.
  • Prometheus Metrics: Exposes metrics for monitoring via Prometheus.

Table of Contents

Introduction

PodConfigMapController automates the management of ConfigMaps based on Pod metadata. It listens to Pod events across all namespaces and ensures that a corresponding ConfigMap is created or deleted when a Pod is created or deleted. The controller can be customized using a CRD and supports leader election for high availability.

Prerequisites

  • Go: Version 1.19 or higher.
  • Kubernetes Cluster: Version 1.28 or compatible.
  • Kubectl: Configured to communicate with your cluster.
  • Docker: For containerizing the controller (optional).
  • Kubernetes Code Generator: If you plan to modify or extend the CRD functionality.

Installation

Clone the Repository

git clone https://github.com/yourusername/PodConfigMapController.git
cd PodConfigMapController

Build The Controller

Ensure you have Go installed and your GOPATH is set up.

go build -o podconfigmapcontroller main.go

Run the Controller

You can run the controller locally for development purposes or for testing.

Running Locally with Kubeconfig

./podconfigmapcontroller --kubeconfig=/path/to/your/kubeconfig

P.S: Replace /path/to/your/kubeconfig with the path to your Kubernetes configuration file. If you're running this within a cluster or the default kubeconfig is sufficient, you can omit the --kubeconfig flag.

Running Inside the Cluster

./podconfigmapcontroller

When running inside the cluster, the controller can use the in-cluster configuration. Ensure that the ServiceAccount running the controller has the necessary permissions.

Containerize and Deploy to Kubernetes

Build Docker Image

Build Dockerfile first in your project dir

FROM golang:1.19 as builder

WORKDIR /app

# Copy the Go modules manifest
COPY go.mod go.sum ./

# Download dependencies
RUN go mod download

# Copy the source code
COPY . .

# Build the controller binary
RUN go build -o podconfigmapcontroller main.go

# Create a minimal image
FROM alpine:latest

# Set working directory
WORKDIR /root/

# Copy the binary from the builder stage
COPY --from=builder /app/podconfigmapcontroller .

# Command to run when starting the container
CMD ["./podconfigmapcontroller"]

Build the Docker image:

docker build -t yourdockerhubusername/podconfigmapcontroller:latest .

Push Docker Image

docker push yourdockerhubusername/podconfigmapcontroller:latest

Deploy to Kubernetes

deployment.yaml (e.g.)

apiVersion: apps/v1
kind: Deployment
metadata:
  name: podconfigmapcontroller
spec:
  replicas: 1
  selector:
    matchLabels:
      app: podconfigmapcontroller
  template:
    metadata:
      labels:
        app: podconfigmapcontroller
    spec:
      serviceAccountName: podconfigmapcontroller-sa
      containers:
        - name: podconfigmapcontroller
          image: yourdockerhubusername/podconfigmapcontroller:latest
          args:
            - --kubeconfig=
          ports:
            - containerPort: 8080
              name: metrics
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: podconfigmapcontroller-sa
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: podconfigmapcontroller-role
rules:
  - apiGroups: [""]
    resources: ["pods", "configmaps"]
    verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]
  - apiGroups: ["coordination.k8s.io"]
    resources: ["leases"]
    verbs: ["get", "create", "update"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: podconfigmapcontroller-rolebinding
subjects:
  - kind: ServiceAccount
    name: podconfigmapcontroller-sa
    namespace: default
roleRef:
  kind: ClusterRole
  name: podconfigmapcontroller-role
  apiGroup: rbac.authorization.k8s.io

Apply the deployment:

kubectl apply -f deployment.yaml

Verify that pods are running:

kubectl get pods

Usage

Once the controller is running, it will automatically watch for Pod events and manage ConfigMaps accordingly. You can test this by creating and deleting Pods:

kubectl run test-pod --image=nginx

Check the logs of the controller to see if it has created a ConfigMap:

kubectl logs deployment/podconfigmapcontroller