server

Defines the address and other parameters of a server. The address can be specified as a domain name or IP address, with an optional port, or as a UNIX-domain socket path specified after the “unix:” prefix. If a port is not specified, the port 80 is used. A domain name that resolves to several IP addresses defines multiple servers at once.

The following parameters can be defined:

weight=number

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

max_conns=number

limits the maximum number of simultaneous active connections to the proxied server (1.11.5). Default value is zero, meaning there is no limit. If the server group does not reside in the shared memory, the limitation works per each worker process.

If idle keepalive connections, multiple workers, and the shared memory are enabled, the total number of active and idle connections to the proxied server may exceed the max_conns value.

Since version 1.5.9 and prior to version 1.11.5, this parameter was available as part of our commercial subscription.

max_fails=number

sets the number of unsuccessful attempts to communicate with the server that should happen in the duration set by the fail_timeout parameter to consider the server unavailable for a duration also set by the fail_timeout parameter. By default, the number of unsuccessful attempts is set to 1. The zero value disables the accounting of attempts. What is considered an unsuccessful attempt is defined by the proxy_next_upstream, fastcgi_next_upstream, uwsgi_next_upstream, scgi_next_upstream, and memcached_next_upstream directives.

fail_timeout=time

sets

• the time during which the specified number of unsuccessful attempts to communicate with the server should happen to consider the server unavailable;
• and the period of time the server will be considered unavailable.

By default, the parameter is set to 10 seconds.

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.

Additionally, the following parameters are available as part of our commercial subscription:

resolve

monitors changes of the IP addresses that correspond to a domain name of the server, and automatically modifies the upstream configuration without the need of restarting nginx (1.5.12). The server group must reside in the shared memory.

In order for this parameter to work, the resolver directive must be specified in the http block. Example:

http {
    resolver 10.0.0.1;

    upstream u {
        zone ...;
        ...
        server example.com resolve;
    }
}

route=string

sets the server route name.

service=name

enables resolving of DNS SRV records and sets the service name (1.9.13). In order for this parameter to work, it is necessary to specify the resolve parameter for the server and specify a hostname without a port number.

If the service name does not contain a dot (“.”), then the RFC-compliant name is constructed and the TCP protocol is added to the service prefix. For example, to look up the _http._tcp.backend.example.com SRV record, it is necessary to specify the directive:

server backend.example.com service=http resolve;

If the service name contains one or more dots, then the name is constructed by joining the service prefix and the server name. For example, to look up the _http._tcp.backend.example.com and server1.backend.example.com SRV records, it is necessary to specify the directives:

server backend.example.com service=_http._tcp resolve;
server example.com service=server1.backend resolve;

Highest-priority SRV records (records with the same lowest-number priority value) are resolved as primary servers, the rest of SRV records are resolved as backup servers. If the backup parameter is specified for the server, high-priority SRV records are resolved as backup servers, the rest of SRV records are ignored.

slow_start=time

sets the time during which the server will recover its weight from zero to a nominal value, when unhealthy server becomes healthy, or when the server becomes available after a period of time it was considered unavailable. Default value is zero, i.e. slow start is disabled.

The parameter cannot be used along with the hash and ip_hash load balancing methods.

If there is only a single server in a group, max_fails, fail_timeout and slow_start parameters are ignored, and such a server will never be considered unavailable.