Day 9: Auto Scaling and Load Balancer – Keep Your App Fast & Available
Category: Compute & High Availability
Goal: Understand how AWS handles high traffic and failures automatically using Auto Scaling and Load Balancing.
🧠 What You’ll Learn Today:
- What is Auto Scaling?
- What is a Load Balancer?
- Why do modern apps need these?
- How AWS helps apps stay online 24/7 — even with 1 user or 10,000
🔁 1. What is Auto Scaling?
Auto Scaling in AWS means:
➡️ Automatically adding or removing EC2 instances based on how much traffic your app is getting.
🔹 Key Points:
- If traffic increases, Auto Scaling launches more EC2 instances
- If traffic drops, it removes extra EC2s to save money
- You set rules (e.g., “Add more EC2s if CPU > 70%”)
- Works with Launch Templates and Target Groups
💡 Example:
Your shopping site gets lots of visitors during a sale. Auto Scaling adds 5 more EC2s. After the sale, it removes them — all done automatically!
🧭 2. What is a Load Balancer?
Load Balancer = A traffic controller that distributes incoming traffic to multiple EC2 instances.
🔹 Key Points:
- Spreads traffic evenly
- Keeps your app fast and available
- Works with Auto Scaling — new instances get added to the Load Balancer automatically
- Supports health checks (removes unhealthy EC2s)
💡 Example:
If 100 users visit your app, the Load Balancer sends 50 to Server A and 50 to Server B — no overload!
⚙️ 3 Types of Load Balancers in AWS:
| Load Balancer Type | Use Case |
|---|---|
| ALB (Application) | For websites & apps (Layer 7) |
| NLB (Network) | For high-performance needs (Layer 4) |
| CLB (Classic) | Older version, less used now |
💡 Beginners should focus on ALB — it’s used for most websites and web apps.
🧩 Auto Scaling + Load Balancer Together
They work hand in hand:
✅ Load Balancer sends traffic to all EC2s
✅ Auto Scaling adds/removes EC2s based on load
✅ This keeps your app fast, healthy, and cost-efficient
🔐 Why Does This Matter?
- 🟢 High Availability: Your app stays online even if one server crashes
- ⚙️ Performance: Handles more users smoothly
- 💰 Cost Savings: Only pay for what you need
- 🔄 Hands-Free Scaling: Set it once, AWS manages the rest
✅ What You Should Do Today:
- ✅ Watch:
👉 YouTube: “AWS Auto Scaling and Load Balancer for Beginners” - ✅ Explore in AWS Console (Free Tier):
- Go to EC2 → Launch Template
- Explore the “Auto Scaling Groups” section
- Check EC2 → Load Balancers tab
- ✅ Visualize:
- Auto Scaling = Hiring more workers only when needed
- Load Balancer = Manager assigning work evenly to workers
📌 Quick Recap:
| Term | Meaning |
|---|---|
| Auto Scaling | Adds/removes EC2s automatically |
| Load Balancer | Distributes traffic to EC2s |
| ALB | Best for websites and HTTP apps |
🧩 End of Day Notes:
With Auto Scaling and Load Balancer, your app becomes smart — it grows when needed and rests when it can. No more manual server management!
🔁 Navigate the Series:
⬅️Day 8: AWS Global Infrastructure – How AWS Works Around the World
➡️Day 10: AWS Lambda Basics – Run Code Without Managing Servers
