Building on a Base Image

When you start adding multiple services to your app, it’s easiest to just copy a new Dockerfile for each service and tweak a few parameters.

Once you have a few services, that duplication can start to feel messy. Sometimes you update one Dockerfile but forget to update the others. Building all the services is slow.

A common pattern is to create a common base image with the dependencies for multiple services.

With Tilt, you can describe when to re-build each image in the dependency graph.

Building a node_modules Base Image

Let’s look at an example. We want to create a NodeJS server with two Docker images:

  1. A Docker image that contains the node_module dependencies.

  2. A Docker image that contains the server source code.

First we write a Dockerfile for the base node_modules image. We’ll call this image local.tilt.dev/nodejs-express-deps.

# local.tilt.dev/nodejs-express-deps

FROM node:9-alpine
WORKDIR /src
ADD package.json package.json
RUN npm install

Next we’ll create a Dockerfile for the app image. This is just an empty base image to build on.

# local.tilt.dev/nodejs-express-app

FROM local.tilt.dev/nodejs-express-deps

ADD . /src

ENTRYPOINT node server.js

Lastly, we’ll add a Tiltfile that knows how to build both images.

# Configure image build for our external dependencies.
docker_build(
  'local.tilt.dev/nodejs-express-deps',
  './package',
  dockerfile='deps.dockerfile')

# Configure build to copy our source code.
docker_build(
  'local.tilt.dev/nodejs-express-app',
  '.', # build context,
  dockerfile='app.dockerfile')

# Set up the Kubernetes resources.
k8s_yaml('app.yml')

Notice that the Docker build for nodejs-express-deps uses the subdirectory ./package. Tilt will only rebuild this image when files under ./package change.

When you run tilt up, Tilt will build both images, and make sure that the first image gets injected into the second image.

STEP 1/3 — Building Dockerfile: [local.tilt.dev/nodejs-express-deps]
Building Dockerfile:
  # local.tilt.dev/nodejs-express-deps

  FROM node:9-alpine
  WORKDIR /src
  ADD package.json package.json
  RUN npm install

...

STEP 2/3 — Building from scratch: [local.tilt.dev/nodejs-express-app]
Building Dockerfile:
  FROM local.tilt.dev/nodejs-express-deps:tilt-af085becbf6ef0ef

  ADD . /
  ENTRYPOINT node server.js

If you make a change to server.js, Tilt knows it can skip the first image build and just do the second.

Try it Yourself

All the source code for this example is on GitHub.

Try running it yourself with Tilt. Make changes to both package.json and server.js and see how Tilt rebuilds only what has changed.