load balancers
- What they do
- Distribute incoming traffic across multiple targets (EC2 instances, containers, IPs, Lambda functions) in multiple Availability Zones.
- Perform health checks and stop sending traffic to unhealthy targets.
- Give the application a single stable DNS name and enable High Availability.
- Elastic Load Balancing types
- Application Load Balancer (ALB) — Layer 7 (HTTP/HTTPS). Routes on path, host header, query string, and headers. The choice for web apps, microservices, and containers.
- Network Load Balancer (NLB) — Layer 4 (TCP/UDP/TLS). Millions of requests per second, ultra-low latency, static IP per AZ. For extreme performance and non-HTTP protocols.
- Gateway Load Balancer (GWLB) — deploys and scales third-party virtual network appliances (firewalls, IDS/IPS).
- Classic Load Balancer — legacy previous generation; do not choose it for new work.
- Pairs with
- AWS Auto Scaling — the load balancer spreads the traffic, Auto Scaling adds and removes the capacity behind it. Together they give Elasticity.
- Not to be confused with
- Amazon Route 53 — DNS-level routing across Regions; ELB balances within a Region.