initial commit

Dockerfile

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+FROM python:3.9-alpine
+
+# Set the working directory
+WORKDIR /app
+
+# Copy the Python files into the container
+COPY main.py k8s_client.py ./
+
+# Install additional dependencies from requirements.txt
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Set the command to run the Python script
+CMD ["python", "main.py"]

README.md

@@ -1 +1,70 @@
-# leader-election
+# Leader Election with Kubernetes ConfigMap
+
+This project demonstrates a leader election algorithm using a ConfigMap in Kubernetes. The algorithm ensures that only one pod becomes the leader and performs specific tasks while other pods wait for their turn.
+
+## Prerequisites
+
+- Kubernetes cluster
+- `kubectl` command-line tool
+- Python 3.6 or later
+
+## Setup
+
+*1.* Clone the repository:
+   ```bash
+   git clone <repository_url>
+   ```
+*2.* Navigate to the project directory:
+```bash
+cd leader-election-k8s-configmap
+```
+
+*3.* Install the required Python packages:
+
+```bash
+pip install -r requirements.txt
+```
+
+## Usage
+Make sure you have a running Kubernetes cluster and the kubectl command-line tool properly configured to access the cluster.
+
+Deploy the leader election application:
+
+```bash
+kubectl apply -f deployment.yaml
+```
+Monitor the logs of the pod to observe the leader election process:
+
+```bash
+kubectl logs -f <pod_name>
+```
+Replace <pod_name> with the name of the pod running the leader election application.
+
+Modify the ConfigMap named leader-election to trigger a change in leadership:
+
+```bash
+kubectl edit configmap leader-election
+```
+This will open the ConfigMap in your default text editor. Modify the leader field to change the leader. Save and close the file.
+
+Note: Ensure that the ConfigMap leader-election exists in the same namespace as the application.
+
+Observe the logs of the leader election application to see the leader change and pod restarts.
+
+## Cleanup
+To clean up the deployed resources, run the following command:
+
+```bash
+kubectl delete -f deployment.yaml
+```
+This will delete the Deployment, and Kubernetes will automatically remove the associated pods.
+
+## Troubleshooting
+If the leader election process or pod restarts are not working as expected, you can check the following:
+
+Verify that the MY_POD_NAME and MY_POD_NAMESPACE environment variables are properly set in the pod.
+Check the logs of the pod for any error messages or issues.
+Ensure that the ConfigMap leader-election exists in the same namespace as the application.
+If you encounter any issues or have questions, please feel free to reach out for assistance.
+
+Happy leader election in Kubernetes!

configmap.yml

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+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: leader-election
+data:
+  leader: ""
+

deployment.yml

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+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: my-deployment
+  labels:
+    app: my-app
+spec:
+  replicas: 4
+  selector:
+    matchLabels:
+      app: my-app
+  template:
+    metadata:
+      labels:
+        app: my-app
+      namespace: $(MY_POD_NAMESPACE)
+    spec:
+      serviceAccountName: pod-deleter
+      containers:
+        - name: my-container
+          image: leader-election:0.0.1
+          command: ["python", "main.py"]
+          env:
+            - name: MY_POD_NAME
+              valueFrom:
+                fieldRef:
+                  fieldPath: metadata.name
+            - name: MY_POD_NAMESPACE
+              valueFrom:
+                fieldRef:
+                  fieldPath: metadata.namespace
+          resources:
+            limits:
+              cpu: 200m
+              memory: 500Mi
+            requests:
+              cpu: 100m
+              memory: 200Mi

k8s_client.py

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+from kubernetes import client, config, watch
+import os
+
+class K8sClient:
+    def __init__(self):
+        # Load the kube config
+        config.load_incluster_config()
+        self.v1 = client.CoreV1Api()
+
+    def get_leader(self):
+        try:
+            # Get the 'leader-election' ConfigMap from the MY_POD_NAMESPACE namespace
+            pod_namespace = os.getenv('MY_POD_NAMESPACE')
+
+            config_map = self.v1.read_namespaced_config_map("leader-election", pod_namespace)
+            # Return the 'leader' data from the ConfigMap
+            return config_map.data["leader"]
+        except client.exceptions.ApiException as e:
+            # If the ConfigMap doesn't exist or 'leader' key doesn't exist, return None
+            if e.status == 404:
+                return None
+            else:
+                raise
+
+    def set_leader(self):
+        # Get the current pod name from the environment variable
+        pod_name = os.getenv('MY_POD_NAME')
+
+        # Update the 'leader' value in the 'leader-election' ConfigMap
+        pod_namespace = os.getenv('MY_POD_NAMESPACE')
+        try:
+            # Get the existing ConfigMap
+            config_map = self.v1.read_namespaced_config_map("leader-election", pod_namespace)
+            # Update the 'leader' key with the current pod name
+            config_map.data["leader"] = pod_name
+            # Update the ConfigMap
+            self.v1.replace_namespaced_config_map("leader-election", pod_namespace, config_map)
+            print(f"Updated leader to '{pod_name}' in the ConfigMap.")
+        except client.exceptions.ApiException as e:
+            print(f"Failed to update leader in ConfigMap: {e}")
+
+    def watch_configmap(self):
+        # Create a watch object
+        w = watch.Watch()
+
+        # Start watching the 'leader-election' ConfigMap in the 'default' namespace
+        pod_namespace = os.getenv('MY_POD_NAMESPACE')
+        for event in w.stream(self.v1.list_namespaced_config_map, pod_namespace):
+            # If the 'leader-election' ConfigMap is modified
+            if event['object'].metadata.name == "leader-election" and event['type'] == 'MODIFIED':
+                print("ConfigMap 'leader-election' has been modified")
+                # Print the new data
+                print(f"New data: {event['object'].data}")
+                # Stop watching after a change is detected
+                w.stop()
+
+    def restart_pod(self):
+        # Get the pod name from the environment variable set in the Deployment
+        pod_name = os.getenv("MY_POD_NAME")
+
+        # Delete the current pod
+        try:
+            pod_namespace = os.getenv('MY_POD_NAMESPACE')
+            self.v1.delete_namespaced_pod(pod_name, pod_namespace)
+            print(f"Pod {pod_name} deleted successfully. A new one will be recreated automatically.")
+        except client.exceptions.ApiException as e:
+            print(f"Failed to delete pod {pod_name}: {e}")

main.py

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+import os
+import time
+from k8s_client import K8sClient
+
+
+
+def main():
+    k8s = K8sClient()
+    pod_name = os.getenv('MY_POD_NAME')
+    while True:
+        leader = k8s.get_leader()
+        if leader is None or leader == pod_name:
+            # If there is no leader, or if this pod is the leader,
+            # Watch for changes in the ConfigMap
+            k8s.watch_configmap()
+            k8s.restart_pod()
+            time.sleep(5)
+        else:
+            # If this pod is not the leader, try to become the leader
+            k8s.set_leader()
+            time.sleep(5)
+
+if __name__ == '__main__':
+    main()

requirements.txt

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+kubernetes

role-write.yml

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+kind: Role
+apiVersion: rbac.authorization.k8s.io/v1
+metadata:
+  namespace: default
+  name: configmap-writer
+rules:
+- apiGroups: [""]
+  resources: ["configmaps"]
+  verbs: ["get", "update", "delete"]

role.yml

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+kind: Role
+apiVersion: rbac.authorization.k8s.io/v1
+metadata:
+  namespace: default
+  name: configmap-reader
+rules:
+- apiGroups: [""]
+  resources: ["configmaps"]
+  verbs: ["get", "watch", "list"]

rolebinding-write.yml

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+kind: RoleBinding
+apiVersion: rbac.authorization.k8s.io/v1
+metadata:
+  name: configmap-writer-binding
+  namespace: default
+subjects:
+- kind: ServiceAccount
+  name: default
+  namespace: default
+roleRef:
+  kind: Role
+  name: configmap-writer
+  apiGroup: rbac.authorization.k8s.io

rolebinding.yml

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+kind: RoleBinding
+apiVersion: rbac.authorization.k8s.io/v1
+metadata:
+  name: configmap-reader-binding
+  namespace: default
+subjects:
+- kind: ServiceAccount
+  name: default
+  namespace: default
+roleRef:
+  kind: Role
+  name: configmap-reader
+  apiGroup: rbac.authorization.k8s.io

service-account.yml

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+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: pod-deleter
+  namespace: default