Measure twice, cut once: App Performance Monitoring with influxdb-rails

published by Henne
on Cover image: Photo by Fleur on Unsplash

Now that we learned how truly magnificent ActiveSupport::Notifications is in the previous post, let's explore a RubyGem Chris, others and me have built around this: influxdb-rails. Together with even more awesome Software Libre, it will help you to deep dive into your Ruby on Rails application performance.

This post ist part two of a three part series about monitoring your Ruby on Rails app with influxdb-rails. Make sure to check them all out!

Application Performance Monitoring (APM)

I'm not sure we have to discuss this at all anymore, but here is why I think I need application performance monitoring for my Ruby on Rail apps: I'm an expert in using the software I hack. Hence I always travel the happy path, cleverly and unconsciously avoid the pitfalls, use it with forethought of the underlying architecture. Because of that, I usually think my app is fast: perceived performance.

It's not what you look at that matters, it's what you see. โ€“ Henry David Thoreau

That is why I need someone to correct that bias for me, in black and white.

Free Software APM

The good folks at Rails bring the instrumentation framework. InfluxData deliver a time series database. Grafana Labs make a dashboard builder. All we need to do, as so often, is to plug Software Libre together: SUCCE$$!

InfluxDB + Grafana == ๐Ÿงจ

I assume your Rails development environment is already running on Getting InfluxDB and Grafana is a matter of pulling containers these days. You can use this simple docker-compose configuration for running them locally.

# docker-compose.yml
version: "3.7"
    image: influxdb:1.7
      - INFLUXDB_DB=rails
      - INFLUXDB_USER=root
      - INFLUXDB_READ_USER=grafana
      - influxdata:/var/lib/influxdb
      - 8086:8086
    image: grafana/grafana:7.4.5
      - 4000:3000
      - influx
      - grafanadata:/var/lib/grafana

A courageous docker-compose up will boot things and you can access Grafana at (user: admin / password: admin). To read data from the InfluxDB container in Grafana, leave the /datasources InfluxDB defaults alone and configure:

URL: http://influx:8086
Database: rails
User: grafana
Password: grafana

influxdb-rails: ๐Ÿชข things together

The influxdb-rails RubyGem is the missing glue code for making your app report metrics into the InfluxDB. Plug it into your Rails app by adding it to your bundle.

bundle add influxdb-rails
bundle exec rails generate influxdb

The next time you boot your Rails dev-env it will start to measure the performance of your app. Now comes the interesting part, interpreting this data with Grafana.

Understanding Ruby on Rails Performance

Every time you use your dev-env, influxdb-rails will write a plethora of performance data into InfluxDB. Let's look at one of the measurements so you get an idea of what's going on. You remember the ActiveSupport::Notification called process_action.action_controller from the previous post? Rails sends this message every time an action in your controller has finished. It includes performance data for this action.

You should know this from somewhere: development.log! It contains the same information.

Started GET "/things" for at 2021-03-25 15:20:14 +0100
Completed 200 OK in 5ms (Views: 4.1ms | ActiveRecord: 0.1ms | Allocations: 3514)

ThingsController#index took 5ms to finish overall, 4.1ms of those 5 in rendering, 0.1ms in querying the database. You find the same data for every request you make in your InfluxDB. Head over to and let Grafana plot it for you.

A Grafana Panel plot

Only want to see how your views are performing? Change the field from controller to view. Magic ๐Ÿช„ But this is only one out of many different ways to look at this measurement. All of the panels below use this one measurement and the data it brings to visualize controller actions.

Many different Grafana panel plots

And this is only one measurement, influxdb-rails reports around a dozen. Now I could send you off your way to learn about ALL. THE. SOFTWARE. involved, but that would be mean wouldn't it?

Ruby on Rails Dashboards

We, the Free Software community, are in this together! We collaborate on Ruby on Rails. We work together to make InfluxDB better. We cooperate to improve Grafana. Why not do the same for the dashboards to visualize Rails performance data? Let's collaborate! That is why we have build a couple of dashboards you can import. Just copy and paste the URLs into your Grafana.

Play a little, I will tell you about all the nitty gritty details in the last post of this series: Let's build Software Libre APM together


Any criticism, remarks or praise about this post? Get in touch, I'm looking forward to your input!