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High availability keeps systems running when parts fail. Here is how redundancy and failover work, what each extra nine of uptime really costs, and how to pick the right target.
Cloud & DevOps
What is Load Balancer?
Quick answer
A system that distributes incoming network traffic across multiple servers so no single server is overwhelmed.
Load Balancer, explained
When a website receives more traffic than one server can handle, a load balancer sits in front of a group of servers and spreads requests among them. If one server fails health checks, the load balancer stops sending it traffic, improving availability.
Load balancers use different strategies, such as round robin, which cycles through servers in order, least connections, which picks the least busy server, or routing based on the user's location or request path. They can operate at the network level or the application level, where they can read HTTP details and terminate TLS encryption. Cloud providers offer managed load balancers, and open-source tools like NGINX and HAProxy are widely used for this role.
Related terms
API Gateway
A server that sits in front of backend services and handles routing, authentication, rate limiting, and monitoring for API requests.
Auto ScalingA cloud feature that automatically adds or removes computing resources based on demand, so applications stay responsive without overpaying.
Blue-Green DeploymentA release method that runs two identical production environments and switches traffic from the old one to the new one once it is ready.
KubernetesAn open-source platform that automates deploying, scaling, and managing containerized applications across clusters of machines.
Reverse ProxyA server that sits in front of web servers and forwards client requests to them, adding security, caching, and load balancing.
ThroughputThe actual amount of data or work a system successfully processes in a given period of time.
UptimeThe percentage of time a system, website, or service is operational and available to users.
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