In our last post, we discussed the Read Replica Pattern — a powerful technique to scale read operations. Now let’s look at how to implement it effectively, especially using middleware.

There are two common ways to set this up:

1️⃣ Embed the routing logic directly in the application code

2️⃣ Use database middleware for transparent routing

In this post, we focus on Option 2 — Database Middleware — which acts as a smart proxy between your application and databases.

📦 Real-World Flow:

1️⃣ Alice places an order on Amazon → the request hits the Order Service

2️⃣ Order Service sends queries to the middleware, not directly to the database

3️⃣ Middleware routes writes to the primary DB → data is replicated to replicas

4️⃣ Alice views her order details → read request goes through middleware to a replica

5️⃣ Alice checks her recent order history → another read served by middleware

This middleware uses the MySQL network protocol for seamless communication, making it compatible with standard MySQL clients.

✅ Benefits:

  • Simplified application code: Your app doesn’t need to handle read/write logic
  • Better compatibility: Middleware can work with any MySQL-compatible client
  • Easy database migration: Apps connect to middleware, not directly to DBs

⚠️ Challenges:

  • Added complexity: Middleware itself is a critical system that needs to be highly available
  • Extra latency: Every query now passes through an additional network hop

🔍 Why This Matters:

Using middleware can significantly reduce developer effort and decouple your application from database topology. But like all good things in system design, it comes with trade-offs in performance and complexity.

💬 How are you handling read vs write routing in your systems?

Have you tried using a database middleware like ProxySQL or Vitess?

Let’s share experiences in the comments 👇