http_upstream module#

Module is used to define groups of servers that can be referenced by the proxy_pass, fastcgi_pass, uwsgi_pass, scgi_pass, memcached_pass and grpc_pass directives.

Example Configuration#

upstream backend {
    zone backend 1m;
    server backend1.example.com       weight=5;
    server backend2.example.com:8080;
    server backend3.example.com       service=_example._tcp resolve;
    server unix:/tmp/backend3;

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

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

Directives#

upstream#

Syntax:

upstream name { … }

Default:

—

Context:

http

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 weight=5;
    server 127.0.0.1:8080       max_fails=3 fail_timeout=30s;
    server unix:/tmp/backend3;

    server backup1.example.com  backup;
}

By default, requests are distributed between the servers using a weighted round-robin balancing method. In the above example, each 7 requests will be distributed as follows: 5 requests go to backend1.example.com and one request to each of the second and third servers.

If an error occurs during communication with a server, the request will be passed to the next server, and so on until all of the functioning servers will be tried. If a successful response could not be obtained from any of the servers, the client will receive the result of the communication with the last server.

server#

Syntax:

server address [parameters];

Default:

—

Context:

upstream

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.
Default value is 0, meaning there is no limit. If the server group does not reside in the shared memory, the limitation works per each worker process.

Note

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.

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.
What is considered an unsuccessful attempt is defined by the proxy_next_upstream, fastcgi_next_upstream, uwsgi_next_upstream, scgi_next_upstream, memcached_next_upstream, and grpc_next_upstream directives.

max_fails=1

the default number of unsuccessful attempts

max_fails=0

disables the accounting of attempts

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.

Attention

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

New in version 1.1.0.

resolve

allows to monitor changes to the list of IP addresses corresponding to a domain name, and automatically update it without the need of reloading configuration. For this parameter to work, the resolver and resolver_timeout directives should be specified in the upstream block, or inherited from the http.

service= имя

enables resolving of DNS SRV records and sets the service name. 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.

zone#

Syntax:

zone name [size];

Default:

—

Context:

upstream

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.

hash#

Syntax:

hash key [consistent];

Default:

—

Context:

upstream

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. 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.

ip_hash#

Syntax:

ip_hash;

Default:

—

Context:

upstream

Specifies that a group should use a load balancing method where requests are distributed between servers based on client IP addresses. The first three octets of the client IPv4 address, or the entire IPv6 address, are used as a hashing key. The method ensures that requests from the same client will always be passed to the same server except when this server is unavailable. In the latter case client requests will be passed to another server. Most probably, it will always be the same server as well.

If one of the servers needs to be temporarily removed, it should be marked with the down parameter in order to preserve the current hashing of client IP addresses.

upstream backend {
    ip_hash;

    server backend1.example.com;
    server backend2.example.com;
    server backend3.example.com down;
    server backend4.example.com;
}

keepalive#

Syntax:

keepalive connections;

Default:

—

Context:

upstream

Activates the cache for connections to upstream servers.

The connections parameter sets the maximum number of idle keepalive connections to upstream servers that are preserved in the cache of each worker process. When this number is exceeded, the least recently used connections are closed.

Note

It should be particularly noted that the keepalive directive does not limit the total number of connections to upstream servers that an Angie worker process can open. The connections parameter should be set to a number small enough to let upstream servers process new incoming connections as well.

Attention

When using load balancing methods other than the default round-robin method, it is necessary to activate them before the keepalive directive.

Example configuration of memcached upstream with keepalive connections:

upstream memcached_backend {
    server 127.0.0.1:11211;
    server 10.0.0.2:11211;

    keepalive 32;
}

server {
    #...

    location /memcached/ {
        set $memcached_key $uri;
        memcached_pass memcached_backend;
    }

}

For HTTP, the proxy_http_version directive should be set to “1.1” and the “Connection” header field should be cleared:

upstream http_backend {
    server 127.0.0.1:8080;

    keepalive 16;
}

server {
    #...

    location /http/ {
        proxy_pass http://http_backend;
        proxy_http_version 1.1;
        proxy_set_header Connection "";
    #    ...
    }
}

Note

Alternatively, HTTP/1.0 persistent connections can be used by passing the “Connection: Keep-Alive” header field to an upstream server, though this method is not recommended.

For FastCGI servers, it is required to set fastcgi_keep_conn for keepalive connections to work:

upstream fastcgi_backend {
    server 127.0.0.1:9000;

    keepalive 8;
}

server {
    #...

    location /fastcgi/ {
        fastcgi_pass fastcgi_backend;
        fastcgi_keep_conn on;
    #    ...
    }
}

Note

SCGI and uwsgi protocols do not have a notion of keepalive connections.

keepalive_requests#

Syntax:

keepalive_requests number;

Default:

keepalive_requests 1000;

Context:

upstream

Sets the maximum number of requests that can be served through one keepalive connection. After the maximum number of requests is made, the connection is closed.

Closing connections periodically is necessary to free per-connection memory allocations. Therefore, using too high maximum number of requests could result in excessive memory usage and not recommended.

keepalive_time#

Syntax:

keepalive_time time;

Default:

keepalive_time 1h;

Context:

upstream

Limits the maximum time during which requests can be processed through one keepalive connection. After this time is reached, the connection is closed following the subsequent request processing.

keepalive_timeout#

Syntax:

keepalive_timeout time;

Default:

keepalive_timeout 60s;

Context:

upstream

Sets a timeout during which an idle keepalive connection to an upstream server will stay open.

least_conn#

Syntax:

least_conn;

Default:

—

Context:

upstream

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. If there are several such servers, they are tried in turn using a weighted round-robin balancing method.

random#

Syntax:

random [two];

Default:

—

Context:

upstream

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

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

resolver#

New in version 1.1.0.

Syntax:

resolver address … [valid= time] [ipv4=on|off] [ipv6=on|off] [status_zone= zone];

Default:

—

Context:

upstream

Configures name servers used to resolve names of upstream servers into addresses, for example:

resolver 127.0.0.1 [::1]:5353;

The address can be specified as a domain name or IP address, with an optional port. If port is not specified, the port 53 is used. Name servers are queried in a round-robin fashion.

By default, Angie caches answers using the TTL value of a response.

valid

optional parameter allows overriding cached entry validity

 
resolver 127.0.0.1 [::1]:5353 valid=30s;

By default, Angie will look up both IPv4 and IPv6 addresses while resolving.

ipv4=off

disables looking up of IPv4 addresses

ipv6=off

disables looking up of IPv6 addresses

status_zone

optional parameter, enables statistics collection for specified zone

Note

To prevent DNS spoofing, it is recommended configuring DNS servers in a properly secured trusted local network.

resolver_timeout#

New in version 1.1.0.

Syntax:

resolver_timeout time;

Default:

resolver_timeout 30s;

Context:

upstream

Sets a timeout for name resolution, for example:

resolver_timeout 5s;

Embedded Variables#

The http_upstream 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. If several servers were contacted during request processing, their addresses are separated by commas, e.g. :

192.168.1.1:80, 192.168.1.2:80, unix:/tmp/sock

If an internal redirect from one server group to another happens, initiated by “X-Accel-Redirect” or error_page, then the server addresses from different groups are separated by colons, e.g.:

192.168.1.1:80, 192.168.1.2:80, unix:/tmp/sock : 192.168.10.1:80, 192.168.10.2:80

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. Values from several connections are separated by commas and colons like addresses in the $upstream_addr variable.

$upstream_bytes_sent#

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

$upstream_cache_status#

keeps the status of accessing a response cache. The status can be either “MISS”, “BYPASS”, “EXPIRED”, “STALE”, “UPDATING”, “REVALIDATED” or “HIT”.

$upstream_connect_time#

keeps time spent on establishing a connection with the upstream server; the time is kept in seconds with millisecond resolution. In case of SSL, includes time spent on handshake. Times of several connections are separated by commas and colons like addresses in the $upstream_addr variable.

$upstream_header_time#

keeps time spent on receiving the response header from the upstream server; the time is kept in seconds with millisecond resolution. Times of several responses are separated by commas and colons like addresses in the $upstream_addr variable.

$upstream_http_ name#

keep server response header fields. For example, the “Server” response header field is available through the $upstream_http_server variable. The rules of converting header field names to variable names are the same as for the variables that start with the “$http_” prefix. Only the header fields from the response of the last server are saved.

$upstream_response_length#

keeps the length of the response obtained from the upstream server; the length is kept in bytes. Lengths of several responses are separated by commas and colons like addresses in the $upstream_addr variable.

$upstream_response_time#

keeps time spent on receiving the response from the upstream server; the time is kept in seconds with millisecond resolution. Times of several responses are separated by commas and colons like addresses in the $upstream_addr variable.

$upstream_status#

keeps status code of the response obtained from the upstream server. Status codes of several responses are separated by commas and colons like addresses in the $upstream_addr variable. If a server cannot be selected, the variable keeps the 502 (Bad Gateway) status code.

$upstream_trailer_ имя#

keeps fields from the end of the response obtained from the upstream server.