Docker Multi Stage Builds

Experimenting with Docker Multi Stage Builds to see image size impact.

Tests

I ran a couple of tests modifying the .dockerignore and Dockerfile using a simple Node ExpressJS app.

App Structure

First I ran npm init -y, then npm i express and npm i -D eslint prettier. After installing all dependencies I created a src dir with a single file called app.js with the following contents:

'uses strict';

const express = require('express');

const app = express();

app.use('/', function(req, res, next) {
  res.json({
    status: 'ok'
  });
});

app.listen(8888);

As well as a .dockerignore, Dockerfile and basic README.md. This gives the following structure:

node_modules
src/
  app.js
.dockerignore
Dockerfile
package-lock.json
package.json
README.md

Test 1 - EMPTY Dockerignore, NO Multi Stage Build

First I wanted to see how the Docker Build Context is affected. Therefore I build an image with an empty .dockerignore using node:9.6 as a base image, without multi stage build.

Navigate to /test-1 and run:

docker build -t msb-node-1 .

DOCKER ARTIFACT	SIZE
Build Context	23.48 MB
Image	680 MB

Test 2 - Dockerignore, NO Multi Stage Build

Now we only send the package files and source code using node:9.6 as a base image, without multi stage build.

Navigate to /test-2 and run:

docker build -t msb-node-2 .

DOCKER ARTIFACT	SIZE
Build Context	57.86 kB
Image	680 MB

Test 3 - Dockerignore, Multi Stage Build

Now we only send the package files and source code using node:9.6 as base images, with multi stage build.

Navigate to /test-3 and run:

docker build -t msb-node-3 .

DOCKER ARTIFACT	SIZE
Build Context	57.86 kB
Image	678 MB

Test 4 - Dockerignore, Multi Stage Build, Alpine Base Images

Now we only send the package files and source code using node:9.6-alpine as base images, with multi stage build.

Navigate to /test-4 and run:

docker build -t msb-node-4 .

DOCKER ARTIFACT	SIZE
Build Context	57.86 kB
Image	69.7 MB

😎

The build context size is printed when running the docker build command, for example:

And the image size is printed when running docker images, for example:

Resources

• Docker Multi Staged Build Docs
• Dockerignore Docs
• Codefresh Do Not Ignore Dockerignore Blog Post