Service Limitations

Constraints & Best Practices

Elastic Load Balancer Limits

Load Balancer Limits

Per-region service limits

  • • ALB: 50 per region (soft limit)
  • • NLB: 50 per region (soft limit)
  • • Target groups: 3,000 per region

Target Limits

Targets per load balancer

  • • ALB: 1,000 targets per target group
  • • NLB: 3,000 targets per target group
  • • Multiple target groups per ALB

Listener Rules

Routing rule constraints

  • • 100 rules per ALB listener
  • • 5 conditions per rule
  • • 5 actions per rule

Auto Scaling Limits

ASG Limits

500 ASGs per region (soft limit)

Launch Templates

10,000 per region, 10,000 versions each

Scaling Policies

50 scaling policies per ASG

Instance Limits

Based on EC2 instance limits per region

Performance Constraints

ELB Warm-up

Cannot handle sudden traffic spikes

Scaling Speed

ASG scaling takes 2-5 minutes

Cooldown Periods

Default 300 seconds between scaling

Health Check Delay

Grace period before health checks start

Important Limitations

Cross-Zone Load Balancing

ALB enabled by default, NLB disabled

  • • ALB: No additional charges
  • • NLB: Additional data transfer charges
  • • Can cause uneven distribution

Session Stickiness

ALB supports, NLB does not

  • • Can cause uneven load distribution
  • • Not recommended for stateless apps
  • • Use external session storage instead

SSL/TLS Termination

Certificate and cipher limitations

  • • 25 certificates per ALB
  • • SNI for multiple certificates
  • • Cipher suite restrictions

Common Pitfalls

Sudden Traffic Spikes

ELB needs pre-warming for large spikes

Aggressive Scaling

Too short cooldown causes thrashing

Single AZ Deployment

Reduces availability and performance

Mitigation Strategies

Request Limit Increases

Contact AWS Support for soft limits

Pre-warm Load Balancers

Contact AWS for expected traffic spikes

Use Multiple Load Balancers

Distribute load across multiple ELBs

Monitor and Alert

Set up CloudWatch alarms for limits

Service Limitations Exam Tips

  • • Most AWS service limits are soft limits that can be increased via support requests
  • • ELB requires pre-warming for sudden traffic spikes - plan ahead for events
  • • Cross-zone load balancing is free for ALB but incurs charges for NLB
  • • Auto Scaling has cooldown periods to prevent rapid scaling - tune appropriately
  • • Always deploy across multiple AZs for high availability and better performance
Previous: Exam Questions Back to HA & Scalability Topics