SCGI#
Allows passing requests to an SCGI server.
When building from the source code, the module is built by
default; it can be disabled with the build option
--without-http_scgi_module.
In packages and images from our repositories, the module is included in the build.
Related guides
Console Light Web Panel: cache zones fill the Caches tab.
Configuration Example#
location / {
include scgi_params;
scgi_pass localhost:9000;
}
Directives#
scgi_bind#
Makes outgoing connections to an 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.
By default, this value is evaluated once when the request is initialized, before
an SCGI server is selected. In Angie PRO, evaluation happens after each SCGI
server selection (including retries), so the bind address can depend on the
selected server; for example, via the $upstream_current_addr variable.
If the evaluated value is empty, no binding is made.
The transparent parameter 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 usually necessary to run Angie 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.
Note
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.
| Angie sends the response to the client in parallel with reading it from the SCGI server; the client does not wait for the whole response. The response is read into the buffers set by the scgi_buffer_size and scgi_buffers directives. A buffer is passed for sending once it is completely filled, and the total size of the buffers busy sending is limited by scgi_busy_buffers_size. A partially filled buffer waits until it fills up or the response ends, so data normally reaches the client in whole buffers. Responses that must reach the client as they are produced therefore need |
| Every portion of data read from the SCGI server is passed to the client immediately, with no minimum size: 10 bytes read from a 4K buffer are sent right away. Angie uses a single buffer, set by the scgi_buffer_size directive, so it reads no more than that size at a time. No temporary file is used, so responses are neither cached nor stored on disk, and neither scgi_limit_rate nor limit_rate has any effect. |
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#
| |
Default |
|
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.
scgi_cache#
Defines a shared memory zone used for caching. The same zone can be used in several places. Parameter value can contain variables.
| disables caching inherited from the previous configuration level. |
Note
When using scgi_cache, you typically need to also set the scgi_cache_valid directive to explicitly specify the caching time for responses. If it's not set, Angie doesn't use default values but determines the response caching time based on HTTP response headers from the server in the following priority order:
The
X-Accel-Expiresheader (highest priority).The
Cache-Controlheader withmax-ageors-maxageparameters.The
Expiresheader.
If none of these headers contain valid values or are not present at all, the response will not be cached because its expiration time cannot be determined.
scgi_cache_background_update#
| |
Default |
|
http, server, location |
Allows starting a background subrequest to update an expired cache item, while a stale cached response is returned to the client.
Warning
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 $http_authorization;
Parameter values can contain variables.
Can be used along with the scgi_no_cache directive.
scgi_cache_key#
Defines a key for caching. The key can contain variables. For example
scgi_cache_key localhost:9000$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 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.
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#
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#
| |
Default |
|
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.
Warning
Cache metadata is stored in shared memory. Manually deleting cache files does not reset the counters and may lead to unpredictable behavior. To completely reset the cache, stop the server, delete the cache directory, and restart.
Note
Third-party cache purge modules (e.g., Cache Purge) only delete files but do not reset the scgi_cache_min_uses counter. The directive is intended to protect the cache from pollution by infrequent requests, and resetting the counter during purge may negatively affect performance.
scgi_cache_path#
| |
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.
| 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.
| determines the directory to be used for temporary files |
| If the parameter is not specified or set to |
| temporary files will be placed directly in the cache directory |
| Sets the name and size of the shared memory zone for storing all active keys and information about data. Cache metadata is stored in shared memory. The zone size is specified in bytes and must be at least two system
memory pages. The A zone of 1 megabyte is sufficient to store about 8000 keys. When an optional file is specified with If the file has incompatible content, for example because an
incompatible build wrote it, Angie renames it with the If the zone size in the configuration no longer matches the size saved
in the file, the configuration fails to load until the file is removed
or the original size is restored. The configuration also fails to load
if the zone cannot be mapped at the memory address saved in the file:
Angie logs Warning Make sure the path to the file is specified correctly and has the necessary access permissions for Angie to use, and is protected from unauthorized access; relative paths are based on the prefix. |
| If cached data is not accessed within the time set by this parameter, it is removed, regardless of its freshness; each access resets this timer. This differs from the size-based eviction performed by the cache manager described below: inactivity-based removal applies even when the cache is below By default, |
A 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.
| maximum threshold value for cache size The value is specified in bytes; the |
| minimum threshold value for free space on the file system with cache The value is specified in the same units as On platforms that do not support querying file system statistics,
the parameter is ignored, and Angie logs the warning
|
| limits the number of items to be deleted during one iteration By default, |
| limits the duration of one iteration By default, |
| configures a pause between iterations By default, |
A minute after Angie 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.
| limits the number of items to load during one iteration By default, |
| limits the duration of one iteration By default, |
| configures a pause between iterations By default, |
scgi_cache_revalidate#
Enables revalidation of expired cache items using conditional requests with the If-Modified-Since and If-None-Match header fields.
scgi_cache_use_stale#
| |
Default |
|
http, server, location |
Determines in which cases a stale cached response can be used. The directive's parameters match the parameters of the scgi_next_upstream directive.
| permits using a stale cached response if an SCGI server to process a request cannot be selected. |
| 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. |
| permits using a stale cached response if a request with a non-idempotent method has already been sent to an SCGI server and communication with that server then fails for any reason; of the non-idempotent methods only |
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-Controlheader field permits using a stale cached response if it is currently being updated.The stale-if-error extension of the
Cache-Controlheader field permits using a stale cached response in case of an error.
Note
This method has lower priority than setting parameters using the directive.
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, it can be specified to cache any responses using the any parameter:
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 caching time using the directive.
The
X-Accel-Expiresheader 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-Expiresfield, parameters of caching may be set in the header fieldsExpiresorCache-Control.If the header includes the
Set-Cookiefield, such a response will not be cached.If the header includes the
Varyfield with the special value "*", such a response will not be cached. If the header includes theVaryfield 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 an SCGI server. It should be noted that this timeout cannot usually exceed 75 seconds.
scgi_connection_drop#
| |
Default |
|
http, server, location |
Enables termination of all active connections to the proxied server after it has been
removed from the group or marked as permanently unavailable by a reresolve process or the API command
DELETE.
Idle connections in the cache are not affected.
A connection is terminated when the next read or write event is processed for either the client or the proxied server.
Setting time enables a connection termination timeout;
with on set, connections are dropped immediately.
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 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, conversely, the passing of fields needs to be permitted, the scgi_pass_header directive can be used.
scgi_ignore_client_abort#
| |
Default |
|
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.
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, andVaryset the parameters of response caching;X-Accel-Redirectperforms an internal redirect to the specified URI or named location;X-Accel-Limit-Ratesets the rate limit for transmission of a response to a client;X-Accel-Bufferingenables or disables buffering of a response;X-Accel-Charsetsets the desired charset of a response.
scgi_intercept_errors#
Determines whether SCGI server responses with codes greater than or equal to 300 should be passed to a client or be intercepted and redirected to Angie 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.
| disables rate limiting |
Note
The limit is set per a request, and so if Angie 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#
| |
Default |
|
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.
| disables buffering of responses to temporary files |
scgi_next_upstream#
| |
Default |
|
http, server, location |
Specifies in which cases a request should be passed to the next server:
| an error occurred while establishing a connection with the server, passing a request to it, or reading the response header; |
| a timeout has occurred while establishing a connection with the server, passing a request to it, or reading the response header; |
| a server returned an empty or invalid response; |
| a server returned a response with the code 500; |
| a server returned a response with the code 503; |
| a server returned a response with the code 403; |
| a server returned a response with the code 404; |
| a server returned a response with the code 429; |
| normally, requests with a non-idempotent method
( |
| 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.
| are always considered unsuccessful attempts, even if they are not specified in the directive |
| are considered unsuccessful attempts only if they are specified in the directive |
| are 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#
| |
Default |
|
http, server, location |
Limits the time during which a request can be passed to the next server.
| turns off this limitation |
scgi_next_upstream_tries#
| |
Default |
|
http, server, location |
Limits the number of possible tries for passing a request to the next server.
| 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;
Parameter values can contain variables.
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 variables. 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;
# ...
}
In the standard scgi_params file, REQUEST_METHOD is set to
$upstream_request_method.
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 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.
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.
Note
If scgi_pass is specified in a location with a trailing slash in the prefix
(for example, location /name/),
and the auto_redirect directive is set to default,
requests without a trailing slash will be redirected (/name -> /name/).
scgi_pass_header#
Permits passing otherwise disabled header fields from an SCGI server to a client.
scgi_pass_request_body#
| |
Default |
|
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#
| |
Default |
|
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#
| |
Default |
|
http, server, location |
Enables or disables buffering of a client request body.
| the request body is fully read from the client before sending the request to an SCGI server. |
| 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 has 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#
Configures the "TCP keepalive" behavior for outgoing connections to an SCGI server.
| By default, the operating system's settings are in effect for the socket. |
| The SO_KEEPALIVE socket option is turned on for the socket. |
scgi_store#
Enables saving of files to a disk.
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#
| |
Default |
|
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#
| |
Default |
|
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#
| |
Default |
|
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.
Content