Module ngx_stream_upstream_module

Example Configuration Directives      upstream      server      zone      hash      least_conn      random Embedded Variables

The ngx_stream_upstream_module module (1.9.0) is used to define groups of servers that can be referenced by the proxy_pass directive.

Example Configuration

upstream backend {
    hash $remote_addr consistent;

    server backend1.example.com:12345  weight=5;
    server backend2.example.com:12345;
    server unix:/tmp/backend3;

    server backup1.example.com:12345   backup;
    server backup2.example.com:12345   backup;
}

server {
    listen 12346;
    proxy_pass backend;
}

Directives

Defines a group of servers. Servers can listen on different ports. In addition, servers listening on TCP and UNIX-domain sockets can be mixed.

Example:

upstream backend {
    server backend1.example.com:12345 weight=5;
    server 127.0.0.1:12345            max_fails=3 fail_timeout=30s;
    server unix:/tmp/backend2;
    server backend3.example.com:12345 resolve;

    server backup1.example.com:12345  backup;
}

By default, connections are distributed between the servers using a weighted round-robin balancing method. In the above example, each 7 connections will be distributed as follows: 5 connections go to backend1.example.com:12345 and one connection to each of the second and third servers. If an error occurs during communication with a server, the connection will be passed to the next server, and so on until all of the functioning servers will be tried. If communication with all servers fails, the connection will be closed.

Defines the address and other parameters of a server. The address can be specified as a domain name or IP address with an obligatory port, or as a UNIX-domain socket path specified after the “unix:” prefix. 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 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.

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. Here, an unsuccessful attempt is an error or timeout while establishing a connection with the server.

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. Connections to the backup server will be passed when the primary servers are unavailable.

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

down

marks the server as permanently unavailable.

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

Defines the name and size of the shared memory zone that keeps the group’s configuration and run-time state that are shared between worker processes. Several groups may share the same zone. In this case, it is enough to specify the size only once.

Specifies a load balancing method for a server group where the client-server mapping is based on the hashed key value. The key can contain text, variables, and their combinations (1.11.2). Usage example:

hash $remote_addr;

Note that adding or removing a server from the group may result in remapping most of the keys to different servers. The method is compatible with the Cache::Memcached Perl library.

If the consistent parameter is specified, the ketama consistent hashing method will be used instead. The method ensures that only a few keys will be remapped to different servers when a server is added to or removed from the group. This helps to achieve a higher cache hit ratio for caching servers. The method is compatible with the Cache::Memcached::Fast Perl library with the ketama_points parameter set to 160.

Specifies that a group should use a load balancing method where a connection is passed to the server with the least number of active connections, taking into account weights of servers. If there are several such servers, they are tried in turn using a weighted round-robin balancing method.

Specifies that a group should use a load balancing method where a connection is passed to a randomly selected server, taking into account weights of servers.

The optional two parameter instructs nginx to randomly select two servers and then choose a server using the specified method. The default method is least_conn which passes a connection to a server with the least number of active connections.

Embedded Variables

The ngx_stream_upstream_module module supports the following embedded variables:

$upstream_addr

keeps the IP address and port, or the path to the UNIX-domain socket of the upstream server (1.11.4). If several servers were contacted during proxying, their addresses are separated by commas, e.g. “192.168.1.1:12345, 192.168.1.2:12345, unix:/tmp/sock”. If a server cannot be selected, the variable keeps the name of the server group.

$upstream_bytes_received

number of bytes received from an upstream server (1.11.4). Values from several connections are separated by commas like addresses in the $upstream_addr variable.

$upstream_bytes_sent

number of bytes sent to an upstream server (1.11.4). Values from several connections are separated by commas like addresses in the $upstream_addr variable.

$upstream_connect_time

time to connect to the upstream server (1.11.4); the time is kept in seconds with millisecond resolution. Times of several connections are separated by commas like addresses in the $upstream_addr variable.

$upstream_first_byte_time

time to receive the first byte of data (1.11.4); the time is kept in seconds with millisecond resolution. Times of several connections are separated by commas like addresses in the $upstream_addr variable.

$upstream_session_time

session duration in seconds with millisecond resolution (1.11.4). Times of several connections are separated by commas like addresses in the $upstream_addr variable.