Structured logging in Rails

Structured logging in Rails

This post was originally published in Gojeks engineering blog, here, this post is a cross post of the same

If you are on rails, you would have noticed that the rails logs which you get by default are quite verbose and spread across multiple lines, even if the context is of processing just one simple controller action.

What I will discuss in this post is how can one sanitize the logs, without losing out on information along with how you can add additional information for your log lines to make full use of the querying features of your logging platform.

What is not in scope of this blog is setting up the mechanism to push the logs from your rails app to your respective logging platform.

Let’s take the example of a simple health check controller which you would add to just make the health check pass for your rails app deployed on kubernetes

# app/controllers/health_check_controller.rb
class HealthCheckController < ActionController::Base
  def ping
    render json: { success: true, errors: nil, data: 'pong' }, status: :ok

and for the config (shown for the development evironment for this example)

# config/environments/development.rb
Rails.application.configure do
    config.log_tags = [:request_id]
    config.log_level = :debug

A simple route for the GET verb, to call the #ping action in the HealthCheckController

# config/routes.rb
Rails.application.routes.draw do
    get '/ping', to: 'health_check#ping'

This is what the logs would look like for the route ping

[my-app-fbf8d7bfc-wk5cd] I, [2020-07-01T07:19:05.007174 #1]  INFO -- : [ec0ad0ba-dfb2-419b-bd81-5feb7dacb308] Processing by HealthCheckController#ping as HTML
[my-app-fbf8d7bfc-wk5cd] I, [2020-07-01T07:19:05.007874 #1]  INFO -- : [ec0ad0ba-dfb2-419b-bd81-5feb7dacb308] Completed 200 OK in 0ms (Views: 0.2ms)
[my-app-fbf8d7bfc-wk5cd] I, [2020-07-01T07:19:05.290929 #1]  INFO -- : [86332306-62e4-412e-a690-eee8253ab1c8] Started GET "/ping" for at 2020-07-01 07:19:05 +0000
[my-app-fbf8d7bfc-wk5cd] I, [2020-07-01T07:19:05.292363 #1]  INFO -- : [86332306-62e4-412e-a690-eee8253ab1c8] Processing by HealthCheckController#ping as HTML

You can notice a few things here,

Ways to improve this

Taking things one at a time, you can compact out the log so that it stays meaningful and not verbose the way it is right now, by using something like lograge. There are a bunch of other alternatives like and, but I went ahead with lograge since it has been around for sometime now and has a larger adoption, my use case of what I required to do worked, and the use case for this as such was just to have certain things injected in our logs along with json formatted logging, and this worked very well for our use case.

Add lograge in your Gemfile

gem 'lograge', '~> 0.11.2'

and do a $ bundle, after which you need to add setup the configuration as followed

# config/environments/developement.rb
Rails.application.configure do
  config.lograge.formatter =
  config.lograge.enabled = true
  config.lograge.base_controller_class = ['ActionController::Base']
  config.lograge.custom_options = lambda do |event|
      application: Rails.application.class.parent_name,
      host: event.payload[:host],
      remote_ip: event.payload[:remote_ip],
      ip: event.payload[:ip],
      x_forwarded_for: event.payload[:x_forwarded_for],
      params: event.payload[:params].except(*exceptions).to_json,
      rails_env: Rails.env,
      exception: event.payload[:exception]&.first,
      request_id: event.payload[:headers]['action_dispatch.request_id'],

config.lograge.base_controller_class = ['ActionController::Base'], this part assumes that each controller will be inheriting from ActionController::Base, you can include any other controller which doesn’t inherit from the Base controller, in order for lograge to pick it up.

along with

class ApplicationController < ActionController::Base
    protect_from_forgery with: exception

    def append_info_to_payload(payload)
        payload[:host] =
        payload[:remote_ip] = request.remote_ip
        payload[:ip] = request.ip

now if you do a

$ curl -I localhost:3000/ping | grep -i "request"
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
X-Request-Id: 4967a677-ab86-4a10-8a01-ea520951cf46

and check the logs of your rails app

{"level":"INFO","progname":null,"message":"{\"method\":\"GET\",\"path\":\"/ping\",\"format\":\"*/*\",\"controller\":\"HealthCheckController\",\"action\":\"ping\",\"status\":200,\"duration\":8.36,\"view\":0.22,\"db\":0.0,\"request_time\":\"2020-07-07 16:10:17 +0530\",\"application\":\"MyApplication\",\"process_id\":7869,\"params\":\"{}\",\"rails_env\":\"development\",\"request_id\":\"4967a677-ab86-4a10-8a01-ea520951cf46\"}"}

Now the whole log line captures a lot of metadata so that you can debug for each log line, you can also notice that one of the keys present in the log line is the request_id present, in this way, what is happening is, you have a unique trace id for your particular request, which you can do a full text search on your logging platform, if it supports it.

To extend this further, what one can do is capture the request_id, and pass it along the each controller’s flow, to capture it, you can simply do a request.request_id. Not that you have the request_id, if you are doing a Rails.logger.{info|debug} you can use it to log the request_id, this way, the request_id’s generated would now also be propagated to the custom logs which you would be adding to your application. The biggest advantage is, now you can add this request_id to each and Rails.logger.{info|debug} every core flow, which would be logged now, what this gives you is, you can just put the request_id in your search param in your logging platform, and it will give you all the logs which has this key in it.

You would also be able to capture additional information like host, remote_ip, ip of the rails app servicing it. by simply doing, request.remote_ip, request.ip, request.request_id

Why not use lograge for even the custom logger?

Lograge doesn’t support this.

What should I do now to add structured logging for my custom logs

You can add a custom logger for your application and initialize it in your application config for the environments wherever you want it.

only thing you need to add is

# app/logger/log_formatter.rb
class LogFormatter < ::Logger::Formatter
  def call(severity, time, program_name, message)
    message = '' if message.blank?
    severity = '' if message.blank?

      level: severity,
      progname: program_name,
      message: message,
    }.to_json + "\r\n"

initialize it in the application config (development here in this case for this example)

# config/environments/developement.rb
Rails.application.configure do
    config.log_formatter =

and just to test the above out

# app/controllers/health_check_controller.rb
class HealthCheckController < ActionController::Base
  def ping"bazbar, request-id: #{request.request_id}")
    render json: { success: true, errors: nil, data: 'pong' }, status: :ok

How will my logs look like after this?

{"level":"INFO","progname":null,"message":"bazbar, request_id: 4967a677-ab86-4a10-8a01-ea520951cqw3"}
{"level":"INFO","progname":null,"message":"{\"method\":\"GET\",\"path\":\"/ping\",\"format\":\"*/*\",\"controller\":\"HealthCheckController\",\"action\":\"ping\",\"status\":200,\"duration\":8.36,\"view\":0.22,\"db\":0.0,\"request_time\":\"2020-07-07 16:10:17 +0530\",\"application\":\"MyApplication\",\"process_id\":7869,\"params\":\"{}\",\"rails_env\":\"development\",\"request_id\":\"4967a677-ab86-4a10-8a01-ea520951cqw3\"}"}

As you can see, the logs from both

are having

That’s all folks