Uinta

Uinta is a plugin for the default Elixir logger that lowers log volume while maximizing log usefulness. It is not a logger backend, but rather includes Uinta.Formatter which will format logs on top of the default Elixir logger backend.

In addition to the formatter, Uinta also includes Uinta.Plug. The plug is a drop-in replacement for Plug.Logger that will log out the request and response on a single line. It can also put the request info into the top-level JSON for easier parsing by your log aggregator.

Why Uinta?

At Podium we log millions of lines per minute and store around a terabyte of log data per day. A large percentage of those lines are the typical GET / and Sent 200 in 2ms that Phoenix.Logger sends by default. By combining those into a single line, we're able to cut out that percentage of lines so that the indexes in our Elasticsearch cluster will be smaller and searches will be faster.

In addition, about 2/3 of those requests are GraphQL requests. Their first log line simply says POST /graphql every time, which gives us no insight into what the request is actually doing. Uinta.Plug will extract GraphQL query names when they exist to make these log lines more useful without having to enable debug logs: QUERY messagesForLocation (/graphql) or MUTATION createMessage (/graphql).

For smaller organizations, the ability to filter out lines pertaining to certain requests paths can also be useful to cut down on log noise. Kubernetes health checks and other requests don't usually need to show up in the logs, so Uinta.Plug allows you to ignore certain paths as long as they return a 200-level status code.

When set up to do so, Uinta will additionally wrap the log line in a JSON object so that it can more easily be parsed by Fluentbit and other log parsers. This increases log line size, but improves searchability and makes logs more useful.

Installation

The package can be installed by adding uinta to your list of dependencies in mix.exs:

def deps do
  [
    {:uinta, "~> 0.6"}
  ]
end

Formatter Installation

To use the formatter, you'll need to add it to your logger configuration. In your (production) config file, look for a line that looks something like this:

config :logger, :console, format: "[$level] $message\\n"

You'll want to replace it with this:

config :logger, :console, format: {Uinta.Formatter, :format}

Plug Installation

Installation of the plug will depend on how your app currently logs requests. Open YourApp.Endpoint and look for the following line:

plug Plug.Logger

If it exists in your endpoint, replace it with this (using the options you want):

plug Uinta.Plug, json: false, log: :info

You can also perform log sampling by setting the success_log_sampling_ratio. Following is a 20% log sampling

plug Uinta.Plug, success_log_sampling_ratio: 0.2

If your endpoint didn't call Plug.Logger, add the above line above the line that looks like this:

plug Plug.RequestId

Now you will also want to add the following anywhere in your main config file to make sure that you aren't logging each request twice:

config :phoenix, logger: false

Attribution

Much of this work, especially Uinta.Plug, is based on Elixir's Plug.Logger