Kubernetes (often written as K8s) is the most popular tool in the DevOps world today. But if you read the official documentation, it sounds scary and complicated. Let's fix that.
Imagine Kubernetes is the Captain of a massive Cargo Ship. Its job is to manage thousands of shipping containers (your applications) automatically. Here are the top 10 concepts you need to know.
1. The Cluster (The Ship)
A Cluster is just a group of computers working together as one big machine. In our analogy, this is the entire ship. You don't talk to individual computers; you talk to the Cluster, and it figures out the rest.
2. Nodes (Master vs Worker)
A Cluster is made up of computers called Nodes. There are two types:
- Master Node (Control Plane): The Captain. It makes decisions (e.g., "Start 3 apps"). It doesn't run the apps itself.
- Worker Node: The Sailors. These are the servers that actually do the hard work and run your applications.
3. Pod (The Atom)
This is the smallest unit in Kubernetes. You might think K8s manages "Containers" (like Docker), but it actually manages Pods.
4. Deployment (The Manager)
You rarely create a Pod directly. Instead, you create a Deployment. Why?
If you create a Pod and it crashes, it stays dead. If you create a Deployment and say "I want 3 copies," the Deployment acts like a manager. If one Pod crashes, the Deployment immediately notices and starts a new one to keep the count at 3.
5. Service (The Phone Number)
Pods are mortal. They die and get replaced, meaning their IP addresses change constantly. How do users find them?
A Service gives you a stable, permanent IP address. It acts like a Receptionist. You call the Service, and the Service forwards your call to whichever Pod is currently alive and running.
6. Ingress (The Entry Gate)
A Service works inside the cluster. But how does the outside world (the internet) reach your website?
Ingress is the smart door. It sits at the edge and routes traffic based on rules. For example: "If user goes to /store, send them to the Store Service. If they go to /blog, send them to the Blog Service."
7. Namespace (Virtual Walls)
If you have 100 teams using one Cluster, it gets messy. Namespaces allow you to divide the cluster into virtual rooms.
Team A works in the "Dev" namespace, and Team B works in the "Prod" namespace. They cannot accidentally delete each other's work.
8. ConfigMap & Secrets (Settings)
You shouldn't hardcode passwords in your code. K8s separates code from configuration.
- ConfigMap: Stores plain text settings (e.g., "Background Color = Blue").
- Secrets: Stores sensitive data securely (e.g., "Database Password = 12345").
9. Volume (The Hard Drive)
Containers are temporary. If you restart a container, all files inside it are lost. This is bad for databases.
A Persistent Volume (PV) is like an external USB drive plugged into the cluster. Even if the Pod dies, the data on the Volume is safe.
10. Helm (The App Store)
Installing a complex app on K8s involves writing 10+ YAML files. It is tedious.
Helm is the "Package Manager" for Kubernetes (like the App Store or Play Store). Instead of writing files manually, you just type helm install my-database, and it does everything for you.
Conclusion
Kubernetes seems complex because it has many moving parts, but each part solves a specific problem. Once you understand these 10 concepts, you are ready to start your first project!