Module ngx_stream_log_module

Example Configuration

The ngx_stream_log_module module (1.11.4) writes session logs in the specified format.

Example Configuration

log_format basic '$remote_addr [$time_local] '
                 '$protocol $status $bytes_sent $bytes_received '

access_log /spool/logs/nginx-access.log basic buffer=32k;


Syntax: access_log path format [buffer=size] [gzip[=level]] [flush=time] [if=condition];
access_log off;
access_log off;
Context: stream, server

Sets the path, format, and configuration for a buffered log write. Several logs can be specified on the same level. Logging to syslog can be configured by specifying the “syslog:” prefix in the first parameter. The special value off cancels all access_log directives on the current level.

If either the buffer or gzip parameter is used, writes to log will be buffered.

The buffer size must not exceed the size of an atomic write to a disk file. For FreeBSD this size is unlimited.

When buffering is enabled, the data will be written to the file:

  • if the next log line does not fit into the buffer;
  • if the buffered data is older than specified by the flush parameter;
  • when a worker process is re-opening log files or is shutting down.

If the gzip parameter is used, then the buffered data will be compressed before writing to the file. The compression level can be set between 1 (fastest, less compression) and 9 (slowest, best compression). By default, the buffer size is equal to 64K bytes, and the compression level is set to 1. Since the data is compressed in atomic blocks, the log file can be decompressed or read by “zcat” at any time.


access_log /path/to/log.gz basic gzip flush=5m;

For gzip compression to work, nginx must be built with the zlib library.

The file path can contain variables, but such logs have some constraints:

  • the user whose credentials are used by worker processes should have permissions to create files in a directory with such logs;
  • buffered writes do not work;
  • the file is opened and closed for each log write. However, since the descriptors of frequently used files can be stored in a cache, writing to the old file can continue during the time specified by the open_log_file_cache directive’s valid parameter

The if parameter enables conditional logging. A session will not be logged if the condition evaluates to “0” or an empty string.

Syntax: log_format name [escape=default|json|none] string ...;
Context: stream

Specifies the log format, for example:

log_format proxy '$remote_addr [$time_local] '
                 '$protocol $status $bytes_sent $bytes_received '
                 '$session_time "$upstream_addr" '
                 '"$upstream_bytes_sent" "$upstream_bytes_received" "$upstream_connect_time"';

The escape parameter (1.11.8) allows setting json or default characters escaping in variables, by default, default escaping is used. The none parameter (1.13.10) disables escaping.

For default escaping, characters “"”, “\”, and other characters with values less than 32 or above 126 are escaped as “\xXX”. If the variable value is not found, a hyphen (“-”) will be logged.

For json escaping, all characters not allowed in JSON strings will be escaped: characters “"” and “\” are escaped as “\"” and “\\”, characters with values less than 32 are escaped as “\n”, “\r”, “\t”, “\b”, “\f”, or “\u00XX”.

Syntax: open_log_file_cache max=N [inactive=time] [min_uses=N] [valid=time];
open_log_file_cache off;
open_log_file_cache off;
Context: stream, server

Defines a cache that stores the file descriptors of frequently used logs whose names contain variables. The directive has the following parameters:

sets the maximum number of descriptors in a cache; if the cache becomes full the least recently used (LRU) descriptors are closed
sets the time after which the cached descriptor is closed if there were no access during this time; by default, 10 seconds
sets the minimum number of file uses during the time defined by the inactive parameter to let the descriptor stay open in a cache; by default, 1
sets the time after which it should be checked that the file still exists with the same name; by default, 60 seconds
disables caching

Usage example:

open_log_file_cache max=1000 inactive=20s valid=1m min_uses=2;