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logger-socket: Raw-socket-based Logger Library for NGINX (based on nginx-module-lua)


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CentOS/RHEL 7 or Amazon Linux 2

yum -y install
yum -y install lua-resty-logger-socket

CentOS/RHEL 8+, Fedora Linux, Amazon Linux 2023

yum -y install
yum -y install lua5.1-resty-logger-socket

To use this Lua library with NGINX, ensure that nginx-module-lua is installed.

This document describes lua-resty-logger-socket v0.1 released on Feb 18 2015.

lua-resty-logger-socket - nonblocking remote access logging for Nginx


This library is still experimental and under early development.


This lua library is a remote logging module for ngx_lua:

This is aimed to replace Nginx's standard ngx_http_log_module to push access logs to a remote server via an nonblocking socket. A common remote log server supporting sockets is syslog-ng.

This Lua library takes advantage of ngx_lua's cosocket API, which ensures 100% nonblocking behavior.


    server {
        location / {
            log_by_lua '
                local logger = require "resty.logger.socket"
                if not logger.initted() then
                    local ok, err = logger.init{
                        host = 'xxx',
                        port = 1234,
                        flush_limit = 1234,
                        drop_limit = 5678,
                    if not ok then
                        ngx.log(ngx.ERR, "failed to initialize the logger: ",

                -- construct the custom access log message in
                -- the Lua variable "msg"

                local bytes, err = logger.log(msg)
                if err then
                    ngx.log(ngx.ERR, "failed to log message: ", err)


This logger module is designed to be shared inside an Nginx worker process by all the requests. So currently only one remote log server is supported. We may support multiple log server sharding in the future.


syntax: ok, err = logger.init(user_config)

Initialize logger with user configurations. This logger must be initted before use. If you do not initialize the logger, you will get an error.

Available user configurations are listed as follows:

  • flush_limit

    If the buffered messages' size plus the current message size reaches (>=) this limit (in bytes), the buffered log messages will be written to log server. Default to 4096 (4KB).

  • drop_limit

    If the buffered messages' size plus the current message size is larger than this limit (in bytes), the current log message will be dropped because of limited buffer size. Default drop_limit is 1048576 (1MB).

  • timeout

    Sets the timeout (in ms) protection for subsequent operations, including the connect method. Default value is 1000 (1 sec).

  • host

    log server host.

  • port

    log server port number.

  • path

    If the log server uses a stream-typed unix domain socket, path is the socket file path. Note that host/port and path cannot both be empty. At least one must be supplied.

  • max_retry_times

    Max number of retry times after a connect to a log server failed or send log messages to a log server failed.

  • retry_interval

    The time delay (in ms) before retry to connect to a log server or retry to send log messages to a log server, default to 100 (0.1s).

  • pool_size

    Keepalive pool size used by sock:keepalive. Default to 10.

  • max_buffer_reuse

    Max number of reuse times of internal logging buffer before creating a new one (to prevent memory leak).

  • periodic_flush

    Periodic flush interval (in seconds). Set to nil to turn off this feature.

  • ssl

    Boolean, enable or disable connecting via SSL. Default to false.

  • ssl_verify

    Boolean, enable or disable verifying host and certificate match. Default to true.

  • sni_host

    Set the hostname to send in SNI and to use when verifying certificate match.


syntax: initted = logger.initted()

Get a boolean value indicating whether this module has been initted (by calling the init method).


syntax: bytes, err = logger.log(msg)

Log a message. By default, the log message will be buffered in the logger module until flush_limit is reached in which case the logger will flush all the buffered messages to remote log server via a socket. bytes is the number of bytes that successfully buffered in the logger. If bytes is nil, err is a string describing what kind of error happens this time. If bytes is not nil, then err is a previous error message. err can be nil when bytes is not nil.


syntax: bytes, err = logger.flush()

Flushes any buffered messages out to remote immediately. Usually you do not need to call this manually because flushing happens automatically when the buffer is full.


  • Multiple log server sharding and/or failover support.
  • "match_similar" utf8 support test.


Jiale Zhi, CloudFlare Inc.

Yichun Zhang (agentzh), CloudFlare Inc.


You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-logger-socket.