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Load balancing

Round robin

Servers are connected in a circle. A new request goes to the next server in line.

• Skips a server which is down.
• Does not cares about that servers load. It can be very loaded.

Least connected

least_conn- Specifies that a group should use a load balancing method where a request is passed to the server with the least number of active connections, taking into account weights of servers.

Fastest response

least_time - Server with the least average response time and least number of active connection

IP hash

Based on IP.

Generic hash

The server to which a request is sent is determined from a user-defined key which may be a text, variable, or their combination.

Options

weight=number sets the weight of the server, by default, 1.

• max_conns=number def 0
• max_fails def 1
• fail_timeout def 10s
• backup - marks the server as a backup server. It will be passed requests when the primary servers are unavailable.
• down - marks the server as permanently unavailable.

Sticky session

• A client can be hooked to one server based on client’s session. Works for all balancing types.

Slow start

The server slow start feature prevents a recently recovered server from being overwhelmed by connections, which may timeout and cause the server to be marked as failed again.

upstream backend {
    server backend1.example.com       weight=5;
    server backend2.example.com:8080;
    server unix:/tmp/backend3;

    server backup1.example.com:8080   backup;
    server backup2.example.com:8080   backup;
}

server {
    location / {
        proxy_pass http://backend;
    }
}

Resources

• NGINX.org ngx_http_upstream_module

• [Scaling Web Applications with NGINX Load Balancing and Caching

  Datadog](https://youtu.be/jVCYaLEBCpU?list=PLSyMwbwM_tntgUiWx_wzSQsAZmLYdASQB)

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