Archived

10/10/2024 Email Stephen Agneta

ExSyslog

ExSyslog is custom backend for Elixir Logger that logs to syslog by wrapping erlang-syslog.

Requirements

Elixir ~> 1.0

Features

Logs to syslog
Allows adding multiple backends with different configurations (e.g. each backend logs to a different facility with different log level)
Custom log formatter
Built-in JSON formatter

Installation

Add :exsyslog as a dependency in your mix.exs file

defp deps do
  [
    {:exsyslog, "~> 1.0.1"}
  ]
end

Add :exsyslog to your list of included_applications:

def application do
  [included_applications: [:exsyslog]]
end

Configuration

ExSyslog is a Logger custom backend, as such, it relies on Logger application.

On your config.exs file tell Logger that it should add ExSyslog backend

config :logger,
  backends: [
            {ExSyslog, :exsyslog_error},
            {ExSyslog, :exsyslog_debug},
            {ExSyslog, :exsyslog_json}
            ]

With the configuration above, Logger application will add three ExSyslog backend with the name {ExSyslog, :exsyslog_error}, {ExSyslog, :exsyslog_debug} and {ExSyslog, :exsyslog_json}.

You might notice that instead of just passing the Module name, we're passing a tuple with {Module name, backend configuration name}. This allow us to have multiple backends with different configuration. Let's configure the backends:

config :logger, :exsyslog_error,
  level: :error,
  format: "$date $time [$level] $levelpad$node $metadata $message",
  metadata: [:module, :line, :function],
  ident: "MyApplication",
  facility: :local0,
  option: [:pid, :cons]

config :logger, :exsyslog_debug,
  level: :debug,
  format: "$date $time [$level] $message",
  ident: "MyApplication",
  facility: :local1,
  option: [:pid, :perror]

config :logger, :exsyslog_json,
  level: :debug,
  format: "$message",
  formatter: ExSyslog.JsonFormatter,
  metadata: [:module, :line, :function],
  ident: "MyApplication",
  facility: :local1,
  option: :pid

Backend configuration properties

level (optional): the logging level. It defaults to :info
format (optional): Same as :console backend (Logger.Formatter). It defaults to "\n$date $time [$level] $levelpad$node $metadata $message\n"
formatter (optional): Formatter that will be used to format the log. It default to Logger.Formatter
metadata (optional): Same as :console backend Logger.Formatter. It defaults to []
ident (optional): A string that's prepended to every message, and is typically set to the app name. It defaults to "Elixir"
facility (optional): syslog facility to be used. It defaults to :local0. More documentation on erlang-syslog
option (optional): syslog option to be used. It defaults to :ndelay. More documentation on erlang-syslog

Custom Formatters

ExSyslog by default uses Logger.Formatter. However, it comes with a JSON formatter that formats a given log entry to a JSON string. NOTE: ExSyslog.JsonFormatter can be use as an example if one wants to build his own formatter.

To build a custom formatter the formatter needs to implement the following functions:

compile(str) Compiles a format string

compile(binary | nil) :: [Logger.Formatter.pattern | binary]
compile({atom, atom}) :: {atom, atom}

format(format, level, msg, timestamp, metadata, config_metadata) Takes a compiled format and transforms it on a string that will be pass to syslog

format({atom, atom} | [Logger.Formatter.pattern | binary], Logger.level, Logger.message, Logger.Formatter.time, Keyword.t, [atom]) :: IO.chardata

To add the custom formatter you will need to set the formatter property on the configuration as exemplified above with ExSyslog.JsonFormatter

Try it

In another shell:

$ tail -f /var/log/syslog

(Mac users)

$ tail -f /var/log/system.log

NOTE Mac has a funny syslog. Your info logs might not show up. You'll need to configure your Mac syslog.

Clone the project, go to examples/examples1 and run the project ($ iex -S mix).

Erlang/OTP 18 [erts-7.0.2] [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false]

Interactive Elixir (1.0.5) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> Example1.run
2015-09-11 15:26:18.850 [error] nonode@nohost module=Elixir.Example1 function=run/0 line=5  Hello ExSyslog
:ok

You should see on the tail -f something similar to:

exsyslog_error backend

Sep 11 16:26:18 bt.local MyApplication[12833]: 2015-09-11 15:26:18.850 [error] nonode@nohost module=Elixir.Example1 function=run/0 line=5  Hello ExSyslog

exsyslog_debug backend

Sep 11 16:26:18 bt.local MyApplication[12833]: 2015-09-11 15:26:18.850 [error] Hello ExSyslog

exsyslog_json backend

Sep 11 16:26:18 bt.local MyApplication[12833]: {"node":"nonode@nohost","module":"Elixir.Example1","message":"Hello ExSyslog","line":5,"level":"error","function":"run/0"}

Authors

Bruno Tavares (btavares@22cans.com)

License

The source code is released under the MIT License.

Check LICENSE for more information.

cidentertainment/exsyslog