SCGI#
Allows passing requests to SCGI server.
Configuration Example#
location / {
include scgi_params;
scgi_pass localhost:9000;
}
Directives#
scgi_bind#
Makes outgoing connections to a SCGI server originate from the specified local IP address with an optional port. Parameter value can contain variables. The special value off 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 allows outgoing connections to a 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 usually necessary to run Angie PRO worker processes with the superuser privileges. On Linux it is not required as if the transparent parameter is specified, worker processes inherit the CAP_NET_RAW capability from the master process.
Important
It is necessary to configure kernel routing table to intercept network traffic from the SCGI server.
scgi_buffer_size#
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.
scgi_buffering#
Enables or disables buffering of responses from the SCGI server.
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Angie PRO 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. |
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he response is passed to a client synchronously, immediately as it is received. Angie PRO will not try to read the whole response from the SCGI server. The maximum size of the data that Angie PRO 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.
scgi_buffers#
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.
scgi_busy_buffers_size#
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.
scgi_cache#
Defines a shared memory zone used for caching. The same zone can be used in several places. Parameter value can contain variables.
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disables caching inherited from the previous configuration level. |
scgi_cache_background_update#
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Default |
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http, server, location |
Allows starting a background subrequest to update an expired cache item, while a stale cached response is returned to the client.
Attention
Note that it is necessary to allow the usage of a stale cached response when it is being updated.
scgi_cache_bypass#
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 $http_authorization;
Can be used along with the scgi_no_cache directive.
scgi_cache_key#
Defines a key for caching, for example
scgi_cache_key localhost:9000$request_uri;
scgi_cache_lock#
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 a 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.
scgi_cache_lock_age#
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.
scgi_cache_lock_timeout#
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Default |
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http, server, location |
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.
scgi_cache_max_range_offset#
Sets an offset in bytes for byte-range requests. If the range is beyond the offset, the range request will be passed to the SCGI server and the response will not be cached.
scgi_cache_methods#
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Default |
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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.
scgi_cache_min_uses#
Sets the number of requests after which the response will be cached.
scgi_cache_path#
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Default |
— |
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: from 1 to 3, each level accepts values 1 or 2. For example, in the following configuration:
scgi_cache_path /data/angie/cache levels=1:2 keys_zone=one:10m;
file names in a cache will look like this:
/data/angie/cache/c/29/b7f54b2df7773722d382f4809d65029c
A cached response is first written to a temporary file, and then the file is renamed. 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.
The directory for temporary files is set based on the use_temp_path parameter.
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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. |
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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 and the minimum amount of free space on the file system with cache and when the size is exceeded or there is not enough free space, it removes the least recently used data. The data is removed in iterations.
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maximum cache size |
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minimum amount of free space on the file system with cache |
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limits the number of items to be deleted during one iteration |
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limits the duration of one iteration |
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configures a pause between iterations |
A minute after the Angie PRO starts 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 also done in iterations.
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limits the number of items to load during one iteration |
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limits the duration of one iteration |
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configures a pause between iterations |
scgi_cache_revalidate#
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Default |
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http, server, location |
Enables revalidation of expired cache items using conditional requests with the “If-Modified-Since” and “If-None-Match” header fields.
scgi_cache_use_stale#
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Default |
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http, server, location |
Determines in which cases a stale cached response can be used during communication with the SCGI server. The directive’s parameters match the parameters of the scgi_next_upstream directive.
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permits using a stale cached response if a SCGI server to process a request cannot be selected. |
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additional 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. |
Using a stale cached response can also be enabled directly in the response header for a specified number of seconds after the response became stale:
The stale-while-revalidate extension of the “Cache-Control” header field permits using a stale cached response if it is currently being updated.
The stale-if-error extension of the “Cache-Control” header field permits using a stale cached response in case of an error.
Note
This has lower priority than using the directive parameters.
To minimize the number of accesses to SCGI servers when populating a new cache element, the scgi_cache_lock directive can be used.
scgi_cache_valid#
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;
Note
Parameters of caching can also be set directly in the response header. This has higher priority than setting of caching time using the directive
The “X-Accel-Expires” header field sets caching time of a response in seconds. The zero value disables caching for a response. If the value starts with the @ prefix, it sets an absolute time in seconds since Epoch, up to which the response may be cached.
If the header does not include the “X-Accel-Expires” field, parameters of caching may be set in the header fields “Expires” or “Cache-Control”.
If the header includes the “Set-Cookie” field, such a response will not be cached.
If the header includes the “Vary” field with the special value “*”, such a response will not be cached. If the header includes the “Vary” field with another value, such a response will be cached taking into account the corresponding request header fields.
Processing of one or more of these response header fields can be disabled using the scgi_ignore_headers directive.
scgi_connect_timeout#
Defines a timeout for establishing a connection with a SCGI server. It should be noted that this timeout cannot usually exceed 75 seconds.
scgi_force_ranges#
Enables byte-range support for both cached and uncached responses from the SCGI server regardless of the “Accept-Ranges” field in these responses.
scgi_hide_header#
By default, Angie PRO does not pass the header fields “Status” and “X-Accel-…” from the response of a 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.
scgi_ignore_client_abort#
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Default |
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http, server, location |
Determines whether the connection with a SCGI server should be closed when a client closes the connection without waiting for a response.
scgi_ignore_headers#
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”, “X-Accel-Buffering”, “X-Accel-Charset”, “Expires”, “Cache-Control”, “Set-Cookie”, and “Vary”.
If not disabled, processing of these header fields has the following effect:
“X-Accel-Expires”, “Expires”, “Cache-Control”, “Set-Cookie” and “Vary” set the parameters of response caching;
“X-Accel-Redirect” performs an internal redirect to the specified URI;
“X-Accel-Limit-Rate” sets the rate limit for transmission of a response to a client;
“X-Accel-Buffering” enables or disables buffering of a response;
“X-Accel-Charset” sets the desired charset of a response.
scgi_intercept_errors#
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Default |
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http, server, location |
Determines whether SCGI-responses with codes greater than or equal to 300 should be passed to a client or be intercepted and redirected to Angie PRO for processing with the error_page directive.
scgi_limit_rate#
Limits the speed of reading the response from the SCGI server. The rate is specified in bytes per second and can contain variables.
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disables rate limiting |
Note
The limit is set per a request, and so if Angie PRO 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.
scgi_max_temp_file_size#
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Default |
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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.
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disables buffering of responses to temporary files |
Note
This restriction does not apply to responses that will be cached or stored on disk.
scgi_next_upstream#
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Default |
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http, server, location |
Specifies in which cases a request should be passed to the next server in the upstream pool:
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an error occurred while establishing a connection with the server, passing a request to it, or reading the response header; |
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a timeout has occurred while establishing a connection with the server, passing a request to it, or reading the response header; |
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a server returned an empty or invalid response; |
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a server returned a response with the code 500; |
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a server returned a response with the code 503; |
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a server returned a response with the code 403; |
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a server returned a response with the code 404; |
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a server returned a response with the code 429; |
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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; enabling this option explicitly allows retrying such requests; |
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disables passing a request to the next server. |
Note
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.
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always considered unsuccessful attempts, even if they are not specified in the directive |
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considered unsuccessful attempts only if they are specified in the directive |
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never considered unsuccessful attempts |
Passing a request to the next server can be limited by the number of tries and by time.
scgi_next_upstream_timeout#
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Default |
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http, server, location |
Limits the time during which a request can be passed to the next server.
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turns off this limitation |
scgi_next_upstream_tries#
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Default |
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http, server, location |
Limits the number of possible tries for passing a request to the next server.
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turns off this limitation |
scgi_no_cache#
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.
scgi_param#
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 configuration 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 then such a parameter will be passed to the server only if its value is not empty:
scgi_param HTTPS $https if_not_empty;
scgi_pass#
Sets the address of an SCGI server. The address can be specified as a domain name or IP address, and an optional port:
scgi_pass localhost:9000;
or as a UNIX domain socket path specified after the word unix and enclosed in colons:
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.
Parameter value can contain variables. In this case, if an address is specified as a domain name, the name is searched among the described server groups, and, if not found, is determined using a resolver.
scgi_pass_header#
Permits passing otherwise disabled header fields from a SCGI server to a client.
scgi_pass_request_body#
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Default |
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http, server, location |
Indicates whether the original request body is passed to the SCGI server. See also the scgi_pass_request_headers directive.
scgi_pass_request_headers#
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Default |
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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.
scgi_read_timeout#
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.
scgi_request_buffering#
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Default |
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http, server, location |
Enables or disables buffering of a client request body.
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the entire request body is read from the client before sending the request to a SCGI server. |
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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 Angie PRO 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.
scgi_send_timeout#
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.
scgi_socket_keepalive#
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Default |
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http, server, location |
Configures the “TCP keepalive” behavior for outgoing connections to a SCGI server.
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By default, the operating system’s settings are in effect for the socket. |
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The SO_KEEPALIVE socket option is turned on for the socket. |
scgi_store#
Enables saving of files to a disk.
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saves files with paths corresponding to the directives alias or root |
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disables saving of files |
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. 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/;
}
scgi_store_access#
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Default |
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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;
scgi_temp_file_write_size#
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Default |
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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.
scgi_temp_path#
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Default |
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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/angie/scgi_temp 1 2;
a temporary file might look like this:
/spool/angie/scgi_temp/7/45/00000123457
See also the use_temp_path parameter of the scgi_cache_path directive.