Load Balancer

A load balancer is a device or software that distributes incoming client requests across multiple backend servers, with the goal of increasing the system’s capacity and reliability.

• It helps handle high volumes of traffic by distributing requests based on factors such as URL paths, server availability, cache state, and cookies.
• Many load balancers also include security features such as filtering out malicious traffic or unnecessary external data.
• They can also monitor application-level traffic for performance and availability.

If a server becomes unresponsive or fails, the load balancer automatically removes it from the pool of active servers.

This is done using a mechanism called a health check.

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Health Check

A health check is a routine process that checks whether a server or service is functioning correctly.

• It involves sending periodic requests (e.g., to /health, /ping) at defined intervals.
• Parameters such as interval and retry attempts can be configured to determine when a server should be marked as unhealthy.
• For example, if a TCP connection fails to complete the 3-way handshake, the load balancer will treat the server as unhealthy and stop routing traffic to it.

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Redundancy and High Availability

Load balancers often enable server redundancy by operating across two or more servers.

They can assign a virtual IP address that maps to multiple physical servers.

Even if one server fails, the service remains operational and stable, ensuring high availability for users.