Load balancing methods

• round-robin — requests to the application servers are distributed in a round-robin fashion,
• least-connected — next request is assigned to the server with the least number of active connections,
• ip-hash — a hash-function is used to determine what server should be selected for the next request (based on the client’s IP address).

round-robin: Default load balancing configuration

upstream myapp1 {
        server srv1.example.com;
        server srv2.example.com;
        server srv3.example.com;
    }

    server {
        listen 80;

        location / {
            proxy_pass http://myapp1;
        }
    }
}

When setting up load balancing for http, https, FastCGI, uwsgi, SCGI, memcached, or gRPC, use http, https, fastcgi_pass, uwsgi_pass, scgi_pass, memcached_pass, and grpc_pass directives respectively.

Least connected load balancing

    upstream myapp1 {
        least_conn;
        server srv1.example.com;
        server srv2.example.com;
        server srv3.example.com;
    }

ip-hash: Session persistence

upstream myapp1 {
    ip_hash;
    server srv1.example.com;
    server srv2.example.com;
    server srv3.example.com;
}

Weighted load balancing

    upstream myapp1 {
        server srv1.example.com weight=3;
        server srv2.example.com;
        server srv3.example.com;
    }

Health checks

Reverse proxy implementation in nginx includes in-band (or passive) server health checks. If the response from a particular server fails with an error, nginx will mark this server as failed, and will try to avoid selecting this server for subsequent inbound requests for a while.

• max_fails: By default, max_fails is set to 1. When it is set to 0, health checks are disabled for this server.
• fail_timeout: defines how long the server will be marked as failed.By default, the parameter is set to 10 seconds.