Kubernetes Series Part 2 Deep Dive Into Pods Deployments and Services

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Kubernetes Series Part 2: Deep Dive into Pods, Deployments, and Services

Welcome back to my Kubernetes series! In the previous post, we dipped our toes into the world of container orchestration and got a taste of Kubernetes with Minikube. Now, it’s time to roll up our sleeves and explore the core building blocks that make Kubernetes tick.

Pods: The Foundation of Kubernetes

Imagine Pods as the smallest deployable units in Kubernetes. They represent a single instance of your application running in a container (or a group of tightly coupled containers). Think of a Pod as a “wrapper” around your container, providing it with the necessary resources and network connectivity within the cluster.

There are two types of Pods:

  • Single-container Pods: The most common type, ideal for running a single, self-contained application component.
  • Multi-container Pods: Useful for scenarios where multiple containers need to share resources, communicate closely, or have dependencies on each other (e.g., an application container and a logging sidecar container).

Understanding the lifecycle of a Pod is crucial for managing your applications. We’ll explore how Pods are created, scheduled onto nodes, run your application code, and eventually terminated in a future post.

Deployments: Managing Pods at Scale

While you can manually create individual Pods, managing them at scale for production applications requires a more robust approach. This is where Deployments come in.

Deployments act as blueprints, defining the desired state of your application. They handle the creation, updating, and scaling of Pods, ensuring that the specified number of replicas (identical copies of your application) are always running.

Deployments also simplify the process of updating your applications with zero downtime. They implement rolling updates, gradually replacing old Pods with new ones, and provide easy rollback mechanisms in case of issues.

Services: Exposing Your Applications

Deployments ensure your applications are running within the cluster, but how do you access them from the outside world or even from other applications within the cluster? This is where Services come into play.

Services provide a stable endpoint to access a group of Pods, abstracting away the underlying complexities of Pod creation, destruction, and dynamic IP addresses.

Kubernetes offers different types of Services:

  • ClusterIP: The default type, providing access to your application from within the cluster.
  • NodePort: Exposes your service on a static port on each node of the cluster, allowing external access.
  • LoadBalancer: Integrates with cloud provider load balancers to distribute traffic to your application from the outside world.

Hands-on Labs

Lab 1: Deploy a simple Nginx web server using Deployments

  kubectl create deployment nginx-deployment --image=nginx:latest --replicas=1

  • Explanation:

    • kubectl create deployment: This command creates a new Pod.
    • nginx-deployment: This is the name you’re giving to your Pod.
    • –image=nginx:latest: This specifies the Docker image to use for the container in your Pod. We’re using the latest version of the official Nginx image.
    • –replicas=1: This tells Kubernetes how many identical Pods of your application you want to run. In this case, you’re starting with one replica.

  • In simpler terms: You’re instructing Kubernetes to create a Deployment named “nginx-deployment.” This Deployment will use the latest Nginx Docker image to create a single Pod, which will run an instance of the Nginx web server.

Lab 2: Expose your Nginx deployment using a Service, making it accessible within the cluster and externally

  kubectl expose deployment nginx-deployment --type=ClusterIP --port=80 --target-port=80

  • Explanation:

    • kubectl expose: This command exposes a Pod as a service.
    • deployment nginx-deployment: This is the name of the Pod you want to expose.
    • –type=ClusterIP: This specifies the type of service you want to create. In this case, it’s a ClusterIP service.
    • –port=80: This is the port that the Service will listen on. Clients within the cluster will connect to this port to access your Nginx web server.
    • –target-port=80: This is the port that the Nginx container inside the Pod is listening on. The Service will forward traffic from port 80 on the Service to port 80 on the Nginx container.

  • In simpler terms: This command creates a way for other applications within your Kubernetes cluster to access your Nginx web server running inside the “nginx-deployment” Deployment. It does this by creating a Service that acts as an internal load balancer, directing traffic to the correct Pod(s) running your Nginx application.

Lab 3: Scale your deployment to handle increased traffic

  kubectl scale deployment nginx-deployment --replicas=2

  • Explaination:

    • kubectl scale deployment: This command instructs Kubernetes to adjust the number of replicas (running instances) of a Deployment.
    • nginx-deployment: This is the name of the Deployment you want to scale. You created this Deployment in a previous step. –replicas=2: This sets the desired number of replicas to 2. Kubernetes will automatically create additional Pods to reach this number.

  • In simpler terms: This command tells Kubernetes to scale your “nginx-deployment” Deployment to have 2 identical Pods running. If you previously had only one replica, Kubernetes will create 1 more Pods to meet the desired replica count. This is useful for handling increased traffic or ensuring high availability for your application.

Lab 4: Perform rolling updates to deploy new versions of your application without downtime

kubectl set image deployment/nginx-deployment nginx=nginx:stable-perl
kubectl rollout restart deployment nginx-deployment

  • Explanation:

    • kubectl rollout restart deployment: This command tells Kubernetes to perform a rolling update on an existing Deployment. A rolling update is a strategy for restarting your application without causing downtime.
    • nginx-deployment: This is the name of the Deployment you want to update. You created this Deployment in a previous step.
    • –image=nginx:latest: This specifies the new Docker image that you want to use for the updated Pods. In this case, you’re updating to the latest version of the official Nginx image.

  • In simpler terms: This command tells Kubernetes to update your “nginx-deployment” Deployment to use the latest version of the Nginx Docker image.