computer science, math, programming and other stuff
a blog by Christopher Swenson

Configuration files in Go

The other day, I was starting to port an existing service I had into Go. There were a lot of issues that I had to tackle to get the functionality I wanted, including being able to run in at least four different environments: test, dev, stage, and prod.

There are a lot of "standard" ways to do this, most focusing on some sort of text or structured file that you load at runtime using file I/O.

However, in dynamic languages, a somewhat common practice is to use a file in that programming language as your configuration. So, in Python, you might have a file that is actual executed Python.

In non-scripting languages, like Java, you normally have an XML, YAML, INI, or JSON file that you read in. But, I've seen at least one non-scripting language, Clojure, that encourages using an executable Clojure file for configuration.

The primary argument against using a file in your programming language itself is that the compile time may be long, and deploying a brand new binary just to change the config file is laborious and slow.

But, I thought, Go doesn't have this limitation: Go compiles super fast, and the binaries tend to be reasonably sized, so deploys won't be that big of a deal.

So, can we just use Go code to be our configuration file?

Definitely. I wrote up a quick template (released under CC0, so feel free to copy and use) for a configuration file in Go. There's a small amount of boilerplate, but it is super easy to compromise.

There are four key parts:

  • var config = getConfig() – this triggers the configuration file to be read at initialization time. You can also use an init() function to do this.
  • type Config struct { ... } – specify all the variables you want in your config file
  • func readConfig() Config { ... } – populate a Config struct based on your environment, which I do via a switch statement.
  • Set your environment (ENV environment variable) when running

That's it. This is a pretty straightforward and easy way to do config files in Go.