Scaling Factors for Load Balancers
Bit the Chipmunk, AWS Expert published on
Hey there, cloud climber! 🧗♂️ Bit here, and today we’re looking at something every AWS networking pro must understand for the exam: how load balancers scale — and what can make them not scale when traffic spikes.
Whether it’s a few nuts or a forest full of users, AWS load balancers grow and shrink to match demand. But they don’t do it magically — there are patterns, limits, and design choices the exam expects you to know. Let’s get into it.
⚙️ 1. How Load Balancers Scale
Each AWS load balancer type scales differently under the hood:
| Type | Scaling Mechanism | Key Factor | Exam Tip |
|---|---|---|---|
| Application Load Balancer (ALB) | Auto-scales horizontally by adding nodes in AZs | Number of new connections and requests per second | May take a few minutes to adapt to sudden traffic spikes — pre-warm for known events |
| Network Load Balancer (NLB) | Scales linearly with new connections; uses AWS Hyperplane | Concurrent connections + PPS (packets per second) | Scales faster than ALB, but backend EC2s must handle increased connections |
| Gateway Load Balancer (GWLB) | Scales transparently with traffic volume | Throughput (Gbps) | Used for inspection appliances; scaling depends on appliance autoscaling |
| Classic Load Balancer (CLB) | (Legacy) Manual pre-warming used to be required | Old exams only! | Rarely appears; know it for migration scenarios only |
🧮 2. Factors That Affect Scaling Performance
Scaling isn’t just about the load balancer itself — it’s about everything connected to it. The exam may describe symptoms like “requests are being dropped under load” or “some AZs are not receiving traffic.” Here’s what to look for:
| Scaling Factor | Impact | Example Exam Clue |
|---|---|---|
| Traffic pattern | Sudden, steep spikes can overwhelm before scaling completes | “Traffic increases from 0 to 100k RPS in 10 seconds” |
| AZ configuration | Load balancer only scales in enabled AZs | “Requests to one AZ fail after instance removal” |
| Target health | Unhealthy or missing targets reduce available capacity | “Traffic shifts to remaining instances, causing throttling” |
| Cross-zone load balancing | Spreads load evenly but adds inter-AZ data transfer (free for ALB, but not for NLB) | “Must evenly balance across AZs without scaling targets in each zone” |
| Idle timeout | Long-lived connections can tie up load balancer resources | “Connections remain open for minutes, limiting new client connections” |
| Backend autoscaling lag | Target group can’t keep up with load balancer scaling | “Targets launch slowly, causing 5xx errors during traffic surge” |
💡 Bit’s Tip: When scaling issues appear in exam questions, look for pre-warming, target health, or zonal imbalance clues.
🚀 3. Pre-Warming and Predictable Spikes
AWS load balancers can handle massive traffic — but if you know a big event is coming (say, a flash sale 🛒), you can request pre-warming through AWS Support.
- When needed: Sudden, step-function increases in new connections or requests.
- How: Provide expected RPS, connection rate, and traffic pattern (burst vs steady).
- Applies to: ALB, NLB, and (historically) CLB.
💬 Exam Example:
“A retailer expects traffic to jump 100× during a 1-hour event. What should they do to ensure the ALB scales in advance?” ✅ Answer: Request pre-warming via AWS Support.
🧱 4. Scaling Across Layers: Load Balancer + Backend
Remember: a load balancer can only pass traffic it receives. You still need to ensure the backend scales too.
| Layer | Scaling Method | Dependency |
|---|---|---|
| Load Balancer | Automatic scaling by AWS | Managed for you, but depends on configuration |
| Target Group | Auto Scaling Group or ECS/EKS scaling | Must react quickly to load changes |
| DNS Layer | Route 53 latency or weighted routing | Distributes traffic globally for multi-region scale |
💡 Bit’s Tip: If an exam question mentions “traffic balanced across multiple Regions for scalability,” the answer is Route 53 — not the load balancer itself.
🧠 5. Exam Traps to Watch Out For
| Trap | Reality |
|---|---|
| “ALB scales instantly to any load.” | ❌ It scales fast but not instantly — warm-up takes time. |
| “NLB always uses cross-zone balancing.” | ❌ It’s disabled by default; must be turned on manually. |
| “Scaling failed — add more EC2s.” | ❌ Check target health, not just instance count. |
| “Load balancer failed — must increase size.” | ❌ They’re managed services — scaling is automatic. |
| “Backend scaled up, but still throttling.” | ❌ The load balancer connection ramp-up may lag behind. |
🌰 Bit’s Recap
Here’s what to remember when the exam gets squirrelly 🐿️:
- ALB: Scales at Layer 7 — watch out for sudden HTTP traffic spikes.
- NLB: Scales faster — great for TCP-heavy or volatile workloads.
- GWLB: Scales transparently — depends on the appliance layer.
- Scaling ≠ instant — warm-up or pre-warming might be required.
- Backends must scale too — load balancers don’t fix slow targets.
Next time you see a question about dropped requests, connection delays, or regional scaling, remember: sometimes the bottleneck isn’t the load balancer — it’s the plan behind it.
Now go grab some scaling snacks — you’ve earned them! 🌰😄