Module ngx_http_scgi_module

Example Configuration
Directives
     scgi_bind
     scgi_buffer_size
     scgi_buffering
     scgi_buffers
     scgi_busy_buffers_size
     scgi_cache
     scgi_cache_bypass
     scgi_cache_key
     scgi_cache_lock
     scgi_cache_lock_age
     scgi_cache_lock_timeout
     scgi_cache_methods
     scgi_cache_min_uses
     scgi_cache_path
     scgi_cache_purge
     scgi_cache_revalidate
     scgi_cache_use_stale
     scgi_cache_valid
     scgi_connect_timeout
     scgi_force_ranges
     scgi_hide_header
     scgi_ignore_client_abort
     scgi_ignore_headers
     scgi_intercept_errors
     scgi_limit_rate
     scgi_max_temp_file_size
     scgi_next_upstream
     scgi_next_upstream_timeout
     scgi_next_upstream_tries
     scgi_no_cache
     scgi_param
     scgi_pass
     scgi_pass_header
     scgi_pass_request_body
     scgi_pass_request_headers
     scgi_read_timeout
     scgi_request_buffering
     scgi_send_timeout
     scgi_store
     scgi_store_access
     scgi_temp_file_write_size
     scgi_temp_path

The ngx_http_scgi_module module allows passing requests to an SCGI server.

Example Configuration

location / {
    include   scgi_params;
    scgi_pass localhost:9000;
}

Directives

Syntax: scgi_bind address [transparent] | off;
Default:
Context: http, server, location

Makes outgoing connections to an SCGI server originate from the specified local IP address with an optional port (1.11.2). Parameter value can contain variables (1.3.12). The special value off (1.3.12) cancels the effect of the scgi_bind directive inherited from the previous configuration level, which allows the system to auto-assign the local IP address and port.

The transparent parameter (1.11.0) allows outgoing connections to an SCGI server originate from a non-local IP address, for example, from a real IP address of a client:

scgi_bind $remote_addr transparent;

In order for this parameter to work, it is necessary to run nginx worker processes with the superuser privileges and configure kernel routing table to intercept network traffic from the SCGI server.

Syntax: scgi_buffer_size size;
Default:
scgi_buffer_size 4k|8k;
Context: http, server, location

Sets the size of the buffer used for reading the first part of the response received from the SCGI server. This part usually contains a small response header. By default, the buffer size is equal to one memory page. This is either 4K or 8K, depending on a platform. It can be made smaller, however.

Syntax: scgi_buffering on | off;
Default:
scgi_buffering on;
Context: http, server, location

Enables or disables buffering of responses from the SCGI server.

When buffering is enabled, nginx receives a response from the SCGI server as soon as possible, saving it into the buffers set by the scgi_buffer_size and scgi_buffers directives. If the whole response does not fit into memory, a part of it can be saved to a temporary file on the disk. Writing to temporary files is controlled by the scgi_max_temp_file_size and scgi_temp_file_write_size directives.

When buffering is disabled, the response is passed to a client synchronously, immediately as it is received. nginx will not try to read the whole response from the SCGI server. The maximum size of the data that nginx can receive from the server at a time is set by the scgi_buffer_size directive.

Buffering can also be enabled or disabled by passing “yes” or “no” in the “X-Accel-Buffering” response header field. This capability can be disabled using the scgi_ignore_headers directive.

Syntax: scgi_buffers number size;
Default:
scgi_buffers 8 4k|8k;
Context: http, server, location

Sets the number and size of the buffers used for reading a response from the SCGI server, for a single connection. By default, the buffer size is equal to one memory page. This is either 4K or 8K, depending on a platform.

Syntax: scgi_busy_buffers_size size;
Default:
scgi_busy_buffers_size 8k|16k;
Context: http, server, location

When buffering of responses from the SCGI server is enabled, limits the total size of buffers that can be busy sending a response to the client while the response is not yet fully read. In the meantime, the rest of the buffers can be used for reading the response and, if needed, buffering part of the response to a temporary file. By default, size is limited by the size of two buffers set by the scgi_buffer_size and scgi_buffers directives.

Syntax: scgi_cache zone | off;
Default:
scgi_cache off;
Context: http, server, location

Defines a shared memory zone used for caching. The same zone can be used in several places. Parameter value can contain variables (1.7.9). The off parameter disables caching inherited from the previous configuration level.

Syntax: scgi_cache_bypass string ...;
Default:
Context: http, server, location

Defines conditions under which the response will not be taken from a cache. If at least one value of the string parameters is not empty and is not equal to “0” then the response will not be taken from the cache:

scgi_cache_bypass $cookie_nocache $arg_nocache$arg_comment;
scgi_cache_bypass $http_pragma    $http_authorization;

Can be used along with the scgi_no_cache directive.

Syntax: scgi_cache_key string;
Default:
Context: http, server, location

Defines a key for caching, for example

scgi_cache_key localhost:9000$request_uri;

Syntax: scgi_cache_lock on | off;
Default:
scgi_cache_lock off;
Context: http, server, location

This directive appeared in version 1.1.12.

When enabled, only one request at a time will be allowed to populate a new cache element identified according to the scgi_cache_key directive by passing a request to an SCGI server. Other requests of the same cache element will either wait for a response to appear in the cache or the cache lock for this element to be released, up to the time set by the scgi_cache_lock_timeout directive.

Syntax: scgi_cache_lock_age time;
Default:
scgi_cache_lock_age 5s;
Context: http, server, location

This directive appeared in version 1.7.8.

If the last request passed to the SCGI server for populating a new cache element has not completed for the specified time, one more request may be passed to the SCGI server.

Syntax: scgi_cache_lock_timeout time;
Default:
scgi_cache_lock_timeout 5s;
Context: http, server, location

This directive appeared in version 1.1.12.

Sets a timeout for scgi_cache_lock. When the time expires, the request will be passed to the SCGI server, however, the response will not be cached.

Before 1.7.8, the response could be cached.

Syntax: scgi_cache_methods GET | HEAD | POST ...;
Default:
scgi_cache_methods GET HEAD;
Context: http, server, location

If the client request method is listed in this directive then the response will be cached. “GET” and “HEAD” methods are always added to the list, though it is recommended to specify them explicitly. See also the scgi_no_cache directive.

Syntax: scgi_cache_min_uses number;
Default:
scgi_cache_min_uses 1;
Context: http, server, location

Sets the number of requests after which the response will be cached.

Syntax: scgi_cache_path path [levels=levels] [use_temp_path=on|off] keys_zone=name:size [inactive=time] [max_size=size] [loader_files=number] [loader_sleep=time] [loader_threshold=time] [purger=on|off] [purger_files=number] [purger_sleep=time] [purger_threshold=time];
Default:
Context: http

Sets the path and other parameters of a cache. Cache data are stored in files. The file name in a cache is a result of applying the MD5 function to the cache key. The levels parameter defines hierarchy levels of a cache. For example, in the following configuration

scgi_cache_path /data/nginx/cache levels=1:2 keys_zone=one:10m;

file names in a cache will look like this:

/data/nginx/cache/c/29/b7f54b2df7773722d382f4809d65029c

A cached response is first written to a temporary file, and then the file is renamed. Starting from version 0.8.9, temporary files and the cache can be put on different file systems. However, be aware that in this case a file is copied across two file systems instead of the cheap renaming operation. It is thus recommended that for any given location both cache and a directory holding temporary files are put on the same file system. A directory for temporary files is set based on the use_temp_path parameter (1.7.10). If this parameter is omitted or set to the value on, the directory set by the scgi_temp_path directive for the given location will be used. If the value is set to off, temporary files will be put directly in the cache directory.

In addition, all active keys and information about data are stored in a shared memory zone, whose name and size are configured by the keys_zone parameter. One megabyte zone can store about 8 thousand keys.

Cached data that are not accessed during the time specified by the inactive parameter get removed from the cache regardless of their freshness. By default, inactive is set to 10 minutes.

The special “cache manager” process monitors the maximum cache size set by the max_size parameter. When this size is exceeded, it removes the least recently used data.

A minute after the start the special “cache loader” process is activated. It loads information about previously cached data stored on file system into a cache zone. The loading is done in iterations. During one iteration no more than loader_files items are loaded (by default, 100). Besides, the duration of one iteration is limited by the loader_threshold parameter (by default, 200 milliseconds). Between iterations, a pause configured by the loader_sleep parameter (by default, 50 milliseconds) is made.

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

purger=on|off
Instructs whether cache entries that match a wildcard key will be removed from the disk by the cache purger (1.7.12). Setting the parameter to on (default is off) will activate the “cache purger” process that permanently iterates through all cache entries and deletes the entries that match the wildcard key.
purger_files=number
Sets the number of items that will be scanned during one iteration (1.7.12). By default, purger_files is set to 10.
purger_threshold=number
Sets the duration of one iteration (1.7.12). By default, purger_threshold is set to 50 milliseconds.
purger_sleep=number
Sets a pause between iterations (1.7.12). By default, purger_sleep is set to 50 milliseconds.

Syntax: scgi_cache_purge string ...;
Default:
Context: http, server, location

This directive appeared in version 1.5.7.

Defines conditions under which the request will be considered a cache purge request. If at least one value of the string parameters is not empty and is not equal to “0” then the cache entry with a corresponding cache key is removed. The result of successful operation is indicated by returning the 204 (No Content) response.

If the cache key of a purge request ends with an asterisk (“*”), all cache entries matching the wildcard key will be removed from the cache. However, these entries will remain on the disk until they are deleted for either inactivity, or processed by the cache purger (1.7.12), or a client attempts to access them.

Example configuration:

scgi_cache_path /data/nginx/cache keys_zone=cache_zone:10m;

map $request_method $purge_method {
    PURGE   1;
    default 0;
}

server {
    ...
    location / {
        scgi_pass        backend;
        scgi_cache       cache_zone;
        scgi_cache_key   $uri;
        scgi_cache_purge $purge_method;
    }
}

This functionality is available as part of our commercial subscription.

Syntax: scgi_cache_revalidate on | off;
Default:
scgi_cache_revalidate off;
Context: http, server, location

This directive appeared in version 1.5.7.

Enables revalidation of expired cache items using conditional requests with the “If-Modified-Since” and “If-None-Match” header fields.

Syntax: scgi_cache_use_stale error | timeout | invalid_header | updating | http_500 | http_503 | http_403 | http_404 | off ...;
Default:
scgi_cache_use_stale off;
Context: http, server, location

Determines in which cases a stale cached response can be used when an error occurs during communication with the SCGI server. The directive’s parameters match the parameters of the scgi_next_upstream directive.

The error parameter also permits using a stale cached response if an SCGI server to process a request cannot be selected.

Additionally, the updating parameter permits using a stale cached response if it is currently being updated. This allows minimizing the number of accesses to SCGI servers when updating cached data.

To minimize the number of accesses to SCGI servers when populating a new cache element, the scgi_cache_lock directive can be used.

Syntax: scgi_cache_valid [code ...] time;
Default:
Context: http, server, location

Sets caching time for different response codes. For example, the following directives

scgi_cache_valid 200 302 10m;
scgi_cache_valid 404      1m;

set 10 minutes of caching for responses with codes 200 and 302 and 1 minute for responses with code 404.

If only caching time is specified

scgi_cache_valid 5m;

then only 200, 301, and 302 responses are cached.

In addition, the any parameter can be specified to cache any responses:

scgi_cache_valid 200 302 10m;
scgi_cache_valid 301      1h;
scgi_cache_valid any      1m;

Parameters of caching can also be set directly in the response header. This has higher priority than setting of caching time using the directive.

Processing of one or more of these response header fields can be disabled using the scgi_ignore_headers directive.

Syntax: scgi_connect_timeout time;
Default:
scgi_connect_timeout 60s;
Context: http, server, location

Defines a timeout for establishing a connection with an SCGI server. It should be noted that this timeout cannot usually exceed 75 seconds.

Syntax: scgi_force_ranges on | off;
Default:
scgi_force_ranges off;
Context: http, server, location

This directive appeared in version 1.7.7.

Enables byte-range support for both cached and uncached responses from the SCGI server regardless of the “Accept-Ranges” field in these responses.

Syntax: scgi_hide_header field;
Default:
Context: http, server, location

By default, nginx does not pass the header fields “Status” and “X-Accel-...” from the response of an SCGI server to a client. The scgi_hide_header directive sets additional fields that will not be passed. If, on the contrary, the passing of fields needs to be permitted, the scgi_pass_header directive can be used.

Syntax: scgi_ignore_client_abort on | off;
Default:
scgi_ignore_client_abort off;
Context: http, server, location

Determines whether the connection with an SCGI server should be closed when a client closes the connection without waiting for a response.

Syntax: scgi_ignore_headers field ...;
Default:
Context: http, server, location

Disables processing of certain response header fields from the SCGI server. The following fields can be ignored: “X-Accel-Redirect”, “X-Accel-Expires”, “X-Accel-Limit-Rate” (1.1.6), “X-Accel-Buffering” (1.1.6), “X-Accel-Charset” (1.1.6), “Expires”, “Cache-Control”, “Set-Cookie” (0.8.44), and “Vary” (1.7.7).

If not disabled, processing of these header fields has the following effect:

Syntax: scgi_intercept_errors on | off;
Default:
scgi_intercept_errors off;
Context: http, server, location

Determines whether an SCGI server responses with codes greater than or equal to 300 should be passed to a client or be redirected to nginx for processing with the error_page directive.

Syntax: scgi_limit_rate rate;
Default:
scgi_limit_rate 0;
Context: http, server, location

This directive appeared in version 1.7.7.

Limits the speed of reading the response from the SCGI server. The rate is specified in bytes per second. The zero value disables rate limiting. The limit is set per a request, and so if nginx simultaneously opens two connections to the SCGI server, the overall rate will be twice as much as the specified limit. The limitation works only if buffering of responses from the SCGI server is enabled.

Syntax: scgi_max_temp_file_size size;
Default:
scgi_max_temp_file_size 1024m;
Context: http, server, location

When buffering of responses from the SCGI server is enabled, and the whole response does not fit into the buffers set by the scgi_buffer_size and scgi_buffers directives, a part of the response can be saved to a temporary file. This directive sets the maximum size of the temporary file. The size of data written to the temporary file at a time is set by the scgi_temp_file_write_size directive.

The zero value disables buffering of responses to temporary files.

This restriction does not apply to responses that will be cached or stored on disk.

Syntax: scgi_next_upstream error | timeout | invalid_header | http_500 | http_503 | http_403 | http_404 | non_idempotent | off ...;
Default:
scgi_next_upstream error timeout;
Context: http, server, location

Specifies in which cases a request should be passed to the next server:

error
an error occurred while establishing a connection with the server, passing a request to it, or reading the response header;
timeout
a timeout has occurred while establishing a connection with the server, passing a request to it, or reading the response header;
invalid_header
a server returned an empty or invalid response;
http_500
a server returned a response with the code 500;
http_503
a server returned a response with the code 503;
http_403
a server returned a response with the code 403;
http_404
a server returned a response with the code 404;
non_idempotent
normally, requests with a non-idempotent method (POST, LOCK, PATCH) are not passed to the next server if a request has been sent to an upstream server (1.9.13); enabling this option explicitly allows retrying such requests;
off
disables passing a request to the next server.

One should bear in mind that passing a request to the next server is only possible if nothing has been sent to a client yet. That is, if an error or timeout occurs in the middle of the transferring of a response, fixing this is impossible.

The directive also defines what is considered an unsuccessful attempt of communication with a server. The cases of error, timeout and invalid_header are always considered unsuccessful attempts, even if they are not specified in the directive. The cases of http_500 and http_503 are considered unsuccessful attempts only if they are specified in the directive. The cases of http_403 and http_404 are never considered unsuccessful attempts.

Passing a request to the next server can be limited by the number of tries and by time.

Syntax: scgi_next_upstream_timeout time;
Default:
scgi_next_upstream_timeout 0;
Context: http, server, location

This directive appeared in version 1.7.5.

Limits the time during which a request can be passed to the next server. The 0 value turns off this limitation.

Syntax: scgi_next_upstream_tries number;
Default:
scgi_next_upstream_tries 0;
Context: http, server, location

This directive appeared in version 1.7.5.

Limits the number of possible tries for passing a request to the next server. The 0 value turns off this limitation.

Syntax: scgi_no_cache string ...;
Default:
Context: http, server, location

Defines conditions under which the response will not be saved to a cache. If at least one value of the string parameters is not empty and is not equal to “0” then the response will not be saved:

scgi_no_cache $cookie_nocache $arg_nocache$arg_comment;
scgi_no_cache $http_pragma    $http_authorization;

Can be used along with the scgi_cache_bypass directive.

Syntax: scgi_param parameter value [if_not_empty];
Default:
Context: http, server, location

Sets a parameter that should be passed to the SCGI server. The value can contain text, variables, and their combination. These directives are inherited from the previous level if and only if there are no scgi_param directives defined on the current level.

Standard CGI environment variables should be provided as SCGI headers, see the scgi_params file provided in the distribution:

location / {
    include scgi_params;
    ...
}

If the directive is specified with if_not_empty (1.1.11) then such a parameter will not be passed to the server until its value is not empty:

scgi_param HTTPS $https if_not_empty;

Syntax: scgi_pass address;
Default:
Context: location, if in location

Sets the address of an SCGI server. The address can be specified as a domain name or IP address, and a port:

scgi_pass localhost:9000;

or as a UNIX-domain socket path:

scgi_pass unix:/tmp/scgi.socket;

If a domain name resolves to several addresses, all of them will be used in a round-robin fashion. In addition, an address can be specified as a server group.

Syntax: scgi_pass_header field;
Default:
Context: http, server, location

Permits passing otherwise disabled header fields from an SCGI server to a client.

Syntax: scgi_pass_request_body on | off;
Default:
scgi_pass_request_body on;
Context: http, server, location

Indicates whether the original request body is passed to the SCGI server. See also the scgi_pass_request_headers directive.

Syntax: scgi_pass_request_headers on | off;
Default:
scgi_pass_request_headers on;
Context: http, server, location

Indicates whether the header fields of the original request are passed to the SCGI server. See also the scgi_pass_request_body directive.

Syntax: scgi_read_timeout time;
Default:
scgi_read_timeout 60s;
Context: http, server, location

Defines a timeout for reading a response from the SCGI server. The timeout is set only between two successive read operations, not for the transmission of the whole response. If the SCGI server does not transmit anything within this time, the connection is closed.

Syntax: scgi_request_buffering on | off;
Default:
scgi_request_buffering on;
Context: http, server, location

This directive appeared in version 1.7.11.

Enables or disables buffering of a client request body.

When buffering is enabled, the entire request body is read from the client before sending the request to an SCGI server.

When buffering is disabled, the request body is sent to the SCGI server immediately as it is received. In this case, the request cannot be passed to the next server if nginx already started sending the request body.

When HTTP/1.1 chunked transfer encoding is used to send the original request body, the request body will be buffered regardless of the directive value.

Syntax: scgi_send_timeout time;
Default:
scgi_send_timeout 60s;
Context: http, server, location

Sets a timeout for transmitting a request to the SCGI server. The timeout is set only between two successive write operations, not for the transmission of the whole request. If the SCGI server does not receive anything within this time, the connection is closed.

Syntax: scgi_store on | off | string;
Default:
scgi_store off;
Context: http, server, location

Enables saving of files to a disk. The on parameter saves files with paths corresponding to the directives alias or root. The off parameter disables saving of files. In addition, the file name can be set explicitly using the string with variables:

scgi_store /data/www$original_uri;

The modification time of files is set according to the received “Last-Modified” response header field. The response is first written to a temporary file, and then the file is renamed. Starting from version 0.8.9, temporary files and the persistent store can be put on different file systems. However, be aware that in this case a file is copied across two file systems instead of the cheap renaming operation. It is thus recommended that for any given location both saved files and a directory holding temporary files, set by the scgi_temp_path directive, are put on the same file system.

This directive can be used to create local copies of static unchangeable files, e.g.:

location /images/ {
    root              /data/www;
    error_page        404 = /fetch$uri;
}

location /fetch/ {
    internal;

    scgi_pass         backend:9000;
    ...

    scgi_store        on;
    scgi_store_access user:rw group:rw all:r;
    scgi_temp_path    /data/temp;

    alias             /data/www/;
}

Syntax: scgi_store_access users:permissions ...;
Default:
scgi_store_access user:rw;
Context: http, server, location

Sets access permissions for newly created files and directories, e.g.:

scgi_store_access user:rw group:rw all:r;

If any group or all access permissions are specified then user permissions may be omitted:

scgi_store_access group:rw all:r;

Syntax: scgi_temp_file_write_size size;
Default:
scgi_temp_file_write_size 8k|16k;
Context: http, server, location

Limits the size of data written to a temporary file at a time, when buffering of responses from the SCGI server to temporary files is enabled. By default, size is limited by two buffers set by the scgi_buffer_size and scgi_buffers directives. The maximum size of a temporary file is set by the scgi_max_temp_file_size directive.

Syntax: scgi_temp_path path [level1 [level2 [level3]]];
Default:
scgi_temp_path scgi_temp;
Context: http, server, location

Defines a directory for storing temporary files with data received from SCGI servers. Up to three-level subdirectory hierarchy can be used underneath the specified directory. For example, in the following configuration

scgi_temp_path /spool/nginx/scgi_temp 1 2;

a temporary file might look like this:

/spool/nginx/scgi_temp/7/45/00000123457

See also the use_temp_path parameter of the scgi_cache_path directive.