mod_log_ringbuffer

Introduction

Sometimes debug logs are too verbose for continuous logging to disk. However occasionally you may be interested in the debug logs when a certain event occurs.

This module allows you to store all logs in a fixed-size buffer in Prosody’s memory, and dump them to a file whenever you want.

Configuration

First of all, you need to load the module by adding it to your global modules_enabled:

modules_enabled = {
    ...
    "log_ringbuffer";
    ...
}

By default the module will do nothing - you need to configure a log sink, using Prosody’s usual logging configuration.

log = {
    -- Log errors to a file
    error = "/var/log/prosody/prosody.err";

    -- Log debug and higher to a 2MB buffer
    { level = "debug", to = "ringbuffer", size = 1024*1024*2, filename = "debug-logs-{pid}-{count}.log", signal = "SIGUSR2" };
}

The possible fields of the logging config entry are:

to
Set this to "ringbuffer".
level
The minimum log level to capture, e.g. "debug".
size
The size, in bytes, of the buffer. When the buffer fills, old data will be overwritten by new data.
lines
If specified, preserves the latest N complete lines in the buffer. The size option is ignored when this option is set.
filename
The name of the file to dump logs to when triggered.
filename_template
This parameter may optionally be specified instead of filename. It may contain a number of variables, described below. Defaults to“{paths.data}/ringbuffer-logs-{pid}-{count}.log”`.

Only one of the following triggers may be specified:

signal
A signal that will cause the buffer to be dumped, e.g. "SIGUSR2". Do not use any signal that is used by any other Prosody module, to avoid conflicts.
event
Alternatively, the name of a Prosody global event that will trigger the logs to be dumped, e.g. "config-reloaded".

Filename variables

If filename_template is specified instead of filename, it may contain any of the following variables in curly braces, e.g. {pid}.

pid
The PID of the current process
count
A counter that begins at 0 and increments for each dump made by the current process.
time
The unix timestamp at which the dump is made. It can be formatted to human-readable local time using {time|yyyymmdd} and {time|hhmmss}.
paths
Allows access to Prosody’s known filesystem paths, use e.g. {paths.data} for the path to Prosody’s data directory.

The filename does not have to be unique for every dump - if a file with the same name already exists, it will be appended to.

Integration with mod_debug_traceback

This module can be used in combination with mod_debug_traceback so that debug logs are dumped at the same time as the traceback. Use the following configuration:

log = {
    ---
    -- other optional logging config here --
    ---

    {
        to = "ringbuffer";
        level = "debug";
        filename_template = "{paths.data}/traceback-{pid}-{count}.log";
        event = "debug_traceback/triggered";
    };
}

If the filename template matches the traceback path, both logs and traceback will be combined into the same file. Of course separate files can be specified if preferred.

Compatibility

0.11 and later.