Load balancers are critical infrastructure components that prevent server overload, eliminate single points of failure, and enable horizontal scaling.
Why it matters
- Ensures application availability even when individual servers fail.
- Enables horizontal scaling by adding servers behind the load balancer.
- Improves response times by routing requests to the least-busy server.
- Required for high-availability architectures and disaster recovery.
- Essential for meeting SLA commitments for uptime and performance.
Load balancing algorithms
- Round Robin: Distributes requests sequentially across servers.
- Least Connections: Routes to the server with fewest active connections.
- Weighted: Assigns proportional traffic based on server capacity.
- IP Hash: Routes requests from the same client IP to the same server (session persistence).
- Least Response Time: Chooses the server with fastest response and fewest connections.
Types of load balancers
- Layer 4 (Transport): Routes based on IP address and TCP/UDP port; fast but less flexible.
- Layer 7 (Application): Routes based on HTTP content (URL, headers, cookies); more intelligent but higher overhead.
- Global (GSLB): Distributes traffic across geographically distributed data centers.
- Internal: Balances traffic between services within a private network.
Health checks
- Active checks: Load balancer periodically probes servers for availability.
- Passive checks: Monitors actual traffic for errors and response times.
- Graceful degradation: Remove unhealthy servers from rotation without dropping connections.
High availability patterns
- Active-Passive: Standby load balancer takes over if primary fails.
- Active-Active: Multiple load balancers share traffic with automatic failover.
- DNS failover: GSLB redirects traffic to healthy data centers.
Cloud implementations
- AWS: Application Load Balancer (ALB), Network Load Balancer (NLB), Classic Load Balancer.
- Azure: Azure Load Balancer, Application Gateway.
- GCP: Cloud Load Balancing (HTTP(S), TCP/UDP, Internal).
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View all termsAPI Gateway
A service that acts as a single entry point for API requests, handling routing, authentication, rate limiting, and other cross-cutting concerns.
Read more →AWS (Amazon Web Services)
Amazon's comprehensive cloud computing platform offering over 200 services for compute, storage, databases, networking, security, and application development.
Read more →Azure (Microsoft Azure)
Microsoft's cloud computing platform providing integrated services for compute, analytics, storage, networking, AI, and enterprise applications.
Read more →CDN (Content Delivery Network)
A geographically distributed network of servers that cache and deliver web content from locations closest to end users, improving performance and reliability.
Read more →Docker
A platform for developing, shipping, and running applications in lightweight, portable containers that package code with all its dependencies.
Read more →Kubernetes
An open-source container orchestration platform that automates deployment, scaling, and management of containerized applications across clusters of hosts.
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