Background

When you deploy an application, our build system fetches all the required dependencies according to the programming language and the requirements of your project. For compiled languages, their executable or package is then built. All these files are gathered in an application image. This image is stored and distributed to our servers when they need to run your application. So one consequence is: the lighter the faster.

Definition

The .slugignore file allows you to list files and directories that should not be included in the image after the build of your application. When you have heavy build dependencies, you often don’t need them after the build, so why keep them? They would only slow down your application’s boot time.

Usage

Create a .slugignore file at the root of your project containing on each line the name of a file or directory you want to exclude from your image.

Each line in the .slugignore is interpreted as it would be in a Linux shell. Hence you can use the * as a wildcard. For instance, *.log would ignore all files ending with .log.

It is also possible to use character range such as [a-f] to remove any file named with a letter between a and f.

Here is an example of a perfectly valid .slugignore file:

[a-f]*.log

This would exclude from the image all files starting by a letter between a and f, followed by any number of characters, and ending with .log.

For a comprehensive list of what is allowed, please refer to the filepath.Match Go function.

Examples

Ruby Application

Your Ruby application doesn’t need to have all its test suites when running in production, so the spec folder can be filtered out:

.slugignore content:

spec

Rails Application

Most Rails applications also use Webpacker to bundle the assets. If this is your case, you can safely remove the following folders that are not necessary to run the application:

doc
/tmp/cache
/node_modules
/.cache/yarn

PHP Application

Some PHP applications also use Webpack (or Webpack Encore) to bundle the assets. If this is your case, you can safely remove the following folders that are not necessary to run the application:

doc
/tmp/cache
/node_modules
/.cache/yarn

Java Application

Your application build process result in a .war file and you don’t want to keep all the generated classes and jar archives from the build:

.slugignore content:

.m2

Go Application

You’re deploying a Go application but you don’t want to keep the Godeps directory containing all the third party dependency source code in the image:

.slugignore content:

Godeps

Next.js Application

You’re deploying a Next.js application but the image size is too big. You can try to run Next.js in standalone mode.

More information here: Next.js in standalone mode.