Awesome
Plug.AccessLog
Plug for writing access logs.
Setup
To use the plug in your projects, edit your mix.exs file and add the project as a dependency:
defp deps do
[
# ...
{:plug_accesslog, "~> 0.15.0"},
# ...
]
end
Usage
Add the plug to your plug pipeline/router:
defmodule AppRouter do
use Plug.Router
plug Plug.AccessLog,
format: :clf,
file: "/path/to/your/logs/access.log"
plug :match
plug :dispatch
get "/hello" do
send_resp(conn, 200, "world")
end
match _ do
send_resp(conn, 404, "oops")
end
end
Note: The usage examples apply to a usecase where your are using plug directly without any framework. Using the plug Plug.AccessLog line in a framework based on plug should be no problem. Please refer to your frameworks individual documentation or source to find a suitable place.
WAL Configuration
All log messages that will be written to a file are collected in a WAL process before actual writing. The messages will be fetched in a configurable interval to be written to the logfiles:
config :plug_accesslog,
:wal,
flush_interval: 100
The time is configured as "milliseconds between writing and flushing". The default value is 100 milliseconds.
Custom Formatters
If you want to extend the formatting capabilities or replace existing ones you can define a custom formatter pipeline to use:
defmodule CustomFormatter do
@behaviour Plug.AccessLog.Formatter
def format(format, conn) do
# manipulate to your liking
format
end
end
defmodule Router do
use Plug.Router
plug Plug.AccessLog,
format: :clf,
formatters: [CustomFormatter, Plug.AccessLog.DefaultFormatter],
file: "/path/to/your/logs/access.log"
end
If you do not configure a list of formatters only the DefaultFormatter will be used. If you define an empty list then no formatting will take place.
All formatters are called in the order they are defined in.
File Configuration
There are two ways to define the file you want log entries to be written to:
defmodule Router do
use Plug.Router
plug Plug.AccessLog, file: "/static/configuration.log"
plug Plug.AccessLog, file: {:system, "SYS_ENV_VAR_WITH_FILE_PATH"}
plug Plug.AccessLog, file: {:system, "SYS_ENV_VAR", "/path/to/default.log"}
end
Do Not Log Filter
To filter the requests before logging you can configure a "do not log" filter function:
defmodule LogFilter do
def dontlog?(%{request_path: "/favicon.ico"}), do: true
def dontlog?(_conn), do: false
end
defmodule Router do
use Plug.Router
plug Plug.AccessLog,
dontlog: &LogFilter.dontlog?/1,
format: :clf,
file: "/path/to/your/logs/access.log"
end
If the function you pass to the plug returns true the request will not be logged.
Logging Functions
To have the parsed log message sent to a logging function instead of writing it to a file you can configure a logging function:
defmodule InfoLogger do
def log(msg), do: Logger.log(:info, msg)
end
defmodule Router do
use Plug.Router
plug Plug.AccessLog,
format: :clf,
fun: &InfoLogger.log/1
end
If a logging function is configured the configured file (if any) will be ignored.
Log Format
The default format is CLF.
Available formats
Besides a self defined format you can use one of the predefined aliases:
:agent
> %{User-Agent}i
> curl/7.35.0
:clf
> %h %l %u %t "%r" %>s %b
> 127.0.0.1 - - [10/Jan/2015:14:46:18 +0100] "GET / HTTP/1.1" 200 31337
:clf_vhost
> %v %h %l %u %t "%r" %>s %b
> www.example.com 127.0.0.1 - - [10/Jan/2015:14:46:18 +0100] "GET / HTTP/1.1" 200 31337
:combined
> %h %l %u %t "%r" %>s %b "%{Referer}i" "%{User-Agent}i"
> 127.0.0.1 - - [22/Jan/2015:19:33:58 +0100] "GET / HTTP/1.1" 200 2 "http://www.example.com/previous_page" "curl/7.35.0"
:combined_vhost
> %v %h %l %u %t "%r" %>s %b "%{Referer}i" "%{User-Agent}i"
> www.example.com 127.0.0.1 - - [22/Jan/2015:19:33:58 +0100] "GET / HTTP/1.1" 200 2 "http://www.example.com/previous_page" "curl/7.35.0"
:referer
> %{Referer}i -> %U
> http://www.example.com/previous_page -> /
For more details about each formatting token and potential modifications please refer to the Plug.AccessLog.DefaultFormatter module.
Benchmarking
A small utility script is provided to check how long it might take to process requests and write the log messages to your disk:
mix run utils/bench.exs
This call will send of a total of 10k requests and wait for them to be written to the disk.
Looking at the data written to utils/bench.log might give a hint at what overhead the log writing is introducing. As with all "benchmarks" of any kind: take the measurements with a pinch of salt and run them in dozens of different conditions yourself.