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Concepts

Backends

A backend is a set of servers that receives forwarded requests. You can add and manage backends via the console.

Frontends

Each Load Balancer is configured with one or several frontends. Each frontend listens to a configured port and has one or multiple backends to which the traffic is forwarded. You can add and manage frontends via the console.

Health checks

Load balancers should only forward traffic to “healthy” backend servers. To monitor the health of a backend server, health checks regularly attempt to connect to backend servers using the protocol and port defined by the forwarding rules to ensure that servers are listening.

High availability

A high availability (HA) setup is an infrastructure without a single point of failure. It prevents a server failure by adding redundancy to every layer of your architecture.

Highly available IP address

This is an IP address, which is, by default, routed to the primary Load Balancer instance. In the event of a primary instance failure this address is automatically re-routed to the replica one. The highly available IP address is automatically created by default, when a Load Balancer is created. It can also be conserved when a Load Balancer is deleted and re-used later.

Load Balancers

Load Balancers are highly available and fully managed instances that allow you to distribute workload across multiple servers. They ensure the scaling of all your applications while securing their continuous availability, even in the event of heavy traffic. They are commonly used to improve the performance and reliability of web sites, applications, databases and other services.

Primary and secondary Load Balancers

Each Load Balancer is implemented with two Instances: a primary Instance and replica (backup) Instance, which provide an active-passive high availability. These Instances are pre-configured which means that if the primary one fails, the replica is ready to handle the traffic. The primary and replica Instances run on different hardware clusters to minimize the risk of simultaneous failure. This also ensures that they do not share physical resources.

Sticky session

A sticky session enables the Load Balancer to bind a user’s session to a specific Instance. This ensures that all subsequent sessions from the user are sent to the same Instance, while there is at least one active session.