ELB & ASG Summary

🛡️ High Availability (HA)

• Runs across multiple Availability Zones 🌍

• Keeps working through failures — an AZ outage, an instance crash

📈 Scalability

🔼 Vertical scaling

• Make each instance bigger

• Example: t2.micro → t2.large

➕ Horizontal scaling

• Add more instances

• Works well with distributed systems

⚡ Elasticity

• Scales up or down automatically based on demand 📈📉

• You only pay for what you're using 💰

🚀 Agility

• Spin resources up or down in minutes

• Speeds up development and deployment

Elastic Load Balancer (ELB)

What it does: Spreads traffic across your EC2 instances

Key features:

• ⚖️ Distributes load

• 🌐 Gives you a single DNS entry point

• 🛡️ Health-checks instances and only routes to healthy ones

• 🌍 Works across multiple AZs for high availability

Types of load balancers:

Auto Scaling Groups (ASG)

What it does: Manages your EC2 instances automatically

Key features:

• ➕ Scales out (adds instances)

• ➖ Scales in (removes instances)

• 🛡️ Replaces unhealthy instances

• 🎯 Keeps capacity at the desired level

Core settings:

Min      = minimum instances allowed
Desired  = target instance count
Max      = upper limit

ELB + ASG: A Powerful Combo

Architecture:

Users 🌍
   ↓
Load Balancer ⚖️
   ↓
Auto Scaling Group ⚙️
   ↓
EC2 Instances (dynamic) 💻

What happens:

• Traffic rises 📈 → ASG adds instances ➕

• Traffic drops 📉 → ASG removes instances ➖

• ELB spreads traffic across whatever's running ⚖️

• An unhealthy instance ❌ gets swapped out automatically 🛡️

Scaling Strategies

Quick Recall

• 🌍 HA → multi-AZ

• 🔼 Vertical → bigger machine

• ➕ Horizontal → more machines

• ⚡ Elasticity → automatic scaling

• 🚀 Agility → fast provisioning

• ⚖️ ELB → traffic distribution

• ⚙️ ASG → instance management

Takeaway

Together, ELB + ASG give you:

• 🌍 High availability

• 📈 Scalability

• ⚡ Elasticity

• 🚀 Agility

Real-world flow:

User traffic 📈
   ↓
ELB distributes ⚖️
   ↓
ASG scales instances ⚙️
   ↓
App stays fast, reliable, and cost-efficient ✅