Product description Fault tolerant load balancer
A fault-tolerant load balancer is a reverse proxy that distributes internet traffic between various Selectel services located in different regions and availability zones:
The load balancer can be used to build fault-tolerant services redundant across multiple regions and hybrid infrastructures based on dedicated servers, cloud servers, and VMware-based public cloud. The load balancer also provides DDoS protection for all incoming traffic at the L3 and L4 levels.
There are no limits on the number of target servers or the volume of traffic transmitted.
Operating principle
To connect a load balancer, you combine your infrastructure into a private network via a Selectel global router, and connect the load balancer to the same network. We provide you with a public IP address for the load balancer to accept traffic; the address is protected against DDoS attacks and advertised to the internet via BGP Anycast. Traffic arriving at the load balancer is distributed across the infrastructure behind it according to the specified rules: balancing algorithm, protocol, IP addresses, and ports of target servers.
The load balancer is redundant across two independent regions—Moscow and St. Petersburg; a high-availability pair of load balancers operates in both regions. If a router or load balancer in one region becomes unavailable, traffic is automatically rerouted to the other region.
Selectel is responsible for configuring the load balancer, ensuring fault tolerance, and monitoring.
Load balancing levels
According to the OSI model, balancing is possible at the following levels:
- L4 over TCP (transport layer) — the load balancer redirects requests to servers according to specified algorithms;
- L7 over HTTP (application layer) — the load balancer analyzes the request content and selects which server to send the request to.
Load balancing algorithms
Different load balancing algorithms are available at both levels (L4, L7):
- Round Robin — a round-robin scheduling algorithm where requests are passed to each server in turn;
- Weighted Round Robin is a weighted round-robin algorithm in which each server is assigned a weight coefficient corresponding to its performance and capacity. Servers with a higher coefficient receive more requests;
- Source IP hash — an algorithm where the preferred server to receive the request is chosen based on an HTTP header or IP address;
- Least Connections — an algorithm where the request is sent to the least loaded server.
Comparison of load balancing levels
Limits
Limits on the number of concurrent connections are set for the high-availability load balancer. The limit depends on the selected billing plan:
- Start — 1 600 connections;
- Basic — 4 000 connections;
- Standard — 8 000 connections;
- Ultra — 80 000 connections.