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

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(poison dependency is set to optional and you should explicitly add it to your dependency list)

Installation

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

Elixir 1.5 and above

defp deps do
  [
    {:ex_syslogger, github: "slashmili/ex_syslogger", tag: "1.4.0"}
  ]
end

Elixir ~> 1.4

defp deps do
  [
    {:ex_syslogger, "~> 1.3"}
  ]
end

Add :ex_syslogger to your list of included_applications:

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

Configuration

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

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

config :logger,
  backends: [
            {ExSyslogger, :ex_syslogger_error},
            {ExSyslogger, :ex_syslogger_debug},
            {ExSyslogger, :ex_syslogger_json}
            ]

With the configuration above, Logger application will add three ExSyslogger backend with the name {ExSyslogger, :ex_syslogger_error}, {ExSyslogger, :ex_syslogger_debug} and {ExSyslogger, :ex_syslogger_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, :ex_syslogger_error,
  level: :error,
  format: "$date $time [$level] $levelpad$node $metadata $message",
  metadata: [:module, :line, :function],
  ident: "MyApplication",
  facility: :local0,
  option: [:pid, :cons]

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

config :logger, :ex_syslogger_json,
  level: :debug,
  format: "$message",
  formatter: ExSyslogger.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 " $date $time [$level] $levelpad$node $metadata $message "
• 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

ExSyslogger by default uses Logger.Formatter. However, it comes with a JSON formatter that formats a given log entry to a JSON string. NOTE: ExSyslogger.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 ExSyslogger.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 ExSyslogger
: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 ExSyslogger

exsyslog_debug backend

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

exsyslog_json backend

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