stream_upstream module

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

Example Configuration

upstream backend {
    hash $remote_addr consistent;
    zone backend 1m;

    server backend1.example.com:1935  weight=5;
    server unix:/tmp/backend3;
    server backend3.example.com       service=_example._tcp resolve;

    server backup1.example.com:1935   backup;
    server backup2.example.com:1935   backup;
}

resolver 127.0.0.53 status_zone=resolver;

server {
    listen 1936;
    proxy_pass backend;
}

Directives

upstream

Syntax:

upstream name { … }

Default:

—

Context:

stream

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:1935 weight=5;
    server 127.0.0.1:1935            max_fails=3 fail_timeout=30s;
    server unix:/tmp/backend2;
    server backend3.example.com:1935 resolve;

    server backup1.example.com:1935  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 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 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.

max_fails=number — sets the number of unsuccessful attempts to communicate with the server that should happen in the duration set by fail_timeout to consider the server unavailable; it is then retried after the same duration.

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

Note

If there’s only one server in an upstream, max_fails has no effect and will be ignored.

max_fails=1	the default number of unsuccessful attempts
max_fails=0	disables the accounting of attempts

fail_timeout=time — sets the period of time during which a number of unsuccessful attempts to communicate with the server (max_fails) should happen to consider the server unavailable. The server then becomes unavailable for the same amount of time before it is retried.

By default, this 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.

Caution

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

Added in version 1.3.0.

resolve

Enables monitoring changes to the list of IP addresses that corresponds to a domain name, updating it without a configuration reload. The group should be stored in a shared memory zone; also, you need to define a resolver.

service=name

Enables resolving DNS SRV records and sets the service name. For this parameter to work, specify the resolve server parameter, providing a hostname without a port number. If there are no dots in the service name, the name is formed according to the RFC standard: the service name is prefixed with _, then _tcp is added after a dot. Thus, the service name http will result in _http._tcp. Angie PRO resolves the SRV records by combining the normalized service name and the hostname and obtaining the list of servers for the combination via DNS, along with their priorities and weights. Top-priority SRV records (ones that share the minimum priority value) resolve into primary servers, and other records become backup servers. If backup is set with server, top-priority SRV records resolve into backup servers, and other records are ignored. Weight influences the selection of servers by the assigned capacity: higher weights receive more requests. If set by both the server directive and the SRV record, the weight set by server is used.

This example will look up the _http._tcp.backend.example.com record:

server backend.example.com service=http resolve;

Added in version 1.4.0.

slow_start=time

sets the time to recover the weight for a server that goes back online, if load balancing uses the round-robin or least_conn method. If the value is set and the server is again considered available and healthy as defined by max_fails and upstream_probe (PRO), the server will steadily recover its designated weight within the allocated timeframe. If the value isn’t set, the server in a similar situation will recover its designated weight immediately.

Note

If there’s only one server in an upstream, slow_start has no effect and will be ignored.

state (PRO)

Added in version 1.4.0: PRO

Syntax:

state file;

Default:

—

Context:

upstream

Specifies the file where the upstream’s server list is persisted. When installing from our packages, a designated /var/lib/angie/state/ (/var/db/angie/state/ on FreeBSD) directory with appropriate permissions is created to store these files, so you will only need to add the file’s basename in the configuration:

upstream backend {

    zone backend 1m;
    state /var/lib/angie/state/<FILE NAME>;
}

The format of this server list is similar to server. The contents of the file change whenever there is any modification to servers in the /config/stream/upstreams/ section via the configuration API. The file is read at Angie PRO start or configuration reload.

Caution

For the state directive to be used in an upstream block, the block should have no server directives; instead, it must have a shared memory zone (zone).

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 (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.

least_conn

Syntax:

least_conn;

Default:

—

Context:

upstream

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.

least_time (PRO)

Syntax:

least_time connect | first_byte | last_byte;

Default:

—

Context:

upstream

Sets the load balancing method for a group where the probability of sending a request to an active server is inversely proportional to the average time it takes to respond; the smaller the response time, the more requests the server will receive.

In the connect mode, the average time to establish the connection is considered; in the first_byte mode, the average time to receive the first byte of the response is considered; in the last_byte mode, the average time to receive the complete response is considered.

The calculation of averages is controlled by the response_time_factor (PRO) directive. Current values are presented as connect_time, first_byte_time, and last_byte_time in the health object of the server among the stream upstream metrics in the API.

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 PRO 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.

response_time_factor (PRO)

Syntax:

response_time_factor number;

Default:

response_time_factor 90;

Context:

upstream

Sets the smoothing factor for the least_time (PRO) load balancing method, using the previous value when calculating the average response time according to the formula of the exponential weighted moving average.

The larger the specified number, the less new values influence the average; if 90 is specified, 90% of the previous value will be taken, and only 10% of the new value. Acceptable values range from 0 to 99 inclusive.

Current calculations are presented as connect_time (time to establish the connection), first_byte_time (time to receive the first byte of the response), and last_byte_time (time to receive the complete response) in the health object of the server among the stream upstream metrics in the API.

Note

Only successful responses are considered in the calculation; what constitutes an unsuccessful response is determined by the proxy_next_upstream directives.

sticky

Added in version 1.6.0: Angie

Added in version 1.6.0: Angie PRO

Syntax:

sticky route $variable…;
sticky learn zone=zone create=$create_var1… lookup=$lookup_var1… [connect] [timeout=time];

Default:

—

Context:

upstream

Configures the binding of client sessions to proxied servers in the mode specified by the first parameter.

Attention

The sticky directive must be used after all directives that set the load balancing method; otherwise, it won’t work.

route modelearn mode (PRO)

This mode uses predefined route identifiers that can be embedded in any connection properties Angie PRO can access. It is less flexible because it relies on predefined values but can suit better if such identifiers are already in place.

Here, when a connection is established with the proxied server, it can assign a route to the client and return its identifier in a manner that they both are aware of. The value of the sid parameter of the server directive must be used as the route identifier. Note that the parameter is additionally hashed if the sticky_secret directive is set.

Subsequent connections from clients that wish to use this route must contain the identifier issued by the server in a way that ensures it ends up in Angie PRO variables.

The directive lists specific variables used for routing. To select the server where the incoming connection is routed, the first non-empty variable is used; it is then compared with the sid parameter of the server directive. If selecting a server fails or the chosen server can’t accept the connection, another server is selected according to the configured balancing method.

Here, Angie PRO looks for the identifier in a custom $route variable, which is mapped from $ssl_preread_server_name (note that ssl_preread must be enabled):

stream {

    map $ssl_preread_server_name $route {

        a.example.com            a;
        b.example.com            b;
        default                  "";
    }

    upstream backend {

        server 127.0.0.1:8081 sid=a;
        server 127.0.0.1:8082 sid=b;

        sticky route $route;
    }

    server {

        listen 127.0.0.1:8080;

        ssl_preread on;

        proxy_pass backend;
    }
}

sticky_strict

Added in version 1.6.0: Angie

Added in version 1.6.0: Angie PRO

Syntax:

sticky_strict on | off;

Default:

sticky_strict off;

Context:

upstream

When enabled, causes Angie PRO to return a connection error to the client if the desired server is unavailable, rather than using any other available server as it would when no servers in the upstream are available.

sticky_secret

Added in version 1.6.0: Angie

Added in version 1.6.0: Angie PRO

Syntax:

sticky_secret string;

Default:

—

Context:

upstream

Adds the string as the salt value to the MD5 hashing function for the sticky directive in the route mode. The string may contain variables, for example, $remote_addr:

upstream backend {
    server 127.0.0.1:8081 sid=a;
    server 127.0.0.1:8082 sid=b;

    sticky route $route;
    sticky_secret my_secret.$remote_addr;
}

Salt is appended to the value being hashed; to verify the hashing mechanism independently:

$ echo -n "<VALUE><SALT>" | md5sum

Built-in Variables

The stream_upstream module supports the following built-in 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. :

192.168.1.1:1935, 192.168.1.2:1935, 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. 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. 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; 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; 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 name

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

$upstream_sticky_status

Status of sticky connections.

""	Connection routed to upstream without sticky enabled.
NEW	Connection without sticky information.
HIT	Connection with sticky information routed to the desired backend.
MISS	Connection with sticky information routed to the backend selected by the load balancing algorithm.

Values from multiple connections are separated by commas and colons, similar to addresses in the $upstream_addr variable.