The Journey from Monolith to Microservices

When software projects start small, it’s common to build everything inside one large application, a monolith.
At first, this works well: everything lives in a single place, it’s easy to manage, and changes are straightforward.

But as the application grows, cracks start to show:

• Scaling is hard: If one feature becomes popular, you can’t scale just that part. You have to scale the entire system.
• Changes are risky: A bug in one part of the system can affect unrelated features.
• Teams move slower: With everyone working on the same codebase, changes can conflict, testing takes longer, and deployments become stressful.

This is where microservices come in. Instead of one giant application, you split your system into smaller, independent services each responsible for one capability.

What Are Microservices?

Microservices are small, independent applications that work together to form a larger system. Each service handles a single responsibility and can be developed, deployed, and scaled independently.

Example

Imagine an e-commerce app:

• In a monolith, you’d have one big application handling user accounts, product catalog, shopping cart, and payments all bundled together.
• In a microservices architecture, you’d split this into separate services:
  • User Service – manages accounts and profiles
  • Catalog Service – manages products
  • Cart Service – handles shopping carts
  • Payment Service – processes payments

Each service has its own codebase, database, and deployment pipeline. If you want to scale only the Payment Service during holiday sales, you can do that without touching the others.

The key distinction is that monoliths bundle everything together, while microservices separate concerns into independently running parts.

Containers: The Building Blocks

Before we can manage microservices effectively, we need a consistent way to package and run them. That’s where containers come in.

A container is like a perfectly packaged box for your application. It includes:

• Your application code
• The runtime (Java, Node.js, etc.)
• Any libraries or dependencies

The beauty of containers is consistency. Whether it runs on your laptop, a staging server, or in the cloud, it behaves the same.
This solves the dreaded “but it worked on my machine!” problem.

The most popular tool for creating containers is Docker. Docker deserves its own deep dive, which we’ll cover separately.

So now, instead of one giant app, you may have 50 microservices, each inside its own container. But managing 50 containers manually across servers? That’s not realistic.

Kubernetes: The Orchestrator

Enter Kubernetes, the system that manages containers at scale.
Imagine you have a huge warehouse (a cluster of servers) and hundreds of container boxes. Kubernetes acts as the automated warehouse manager. It does the following:

• Scheduling: You tell it, “Run 3 copies of my Payment Service.” Kubernetes finds available space in the warehouse and places the boxes there.
• Self-healing: If one box is damaged (a pod crashes), Kubernetes automatically replaces it.
• Scaling: If demand increases, Kubernetes can quickly expand from 3 boxes to 30, and later shrink back down.
• Networking: It ensures that all boxes can communicate with each other without you needing to worry about the wiring.

In short, Kubernetes makes it possible to manage containers efficiently across many servers, so you can focus on applications instead of infrastructure.

Wrapping Up

The journey from monolith to microservices is about moving from “one big application” to a set of smaller, focused services.

• Docker makes it easy to build and run containers.
• Kubernetes makes it possible to operate them reliably at scale.