In this tutorial, we’ll explain how to use
pack and Cloud Native Buildpacks to create a runnable app image from source code.
Let’s start with the basics. A buildpack is something you’ve likely leveraged without knowing, as they’re already being used in many cloud platforms. A buildpack’s job is to gather dependencies your app needs to build and run, and it often does this job quickly and quietly.
That said, while buildpacks are often a behind-the-scenes detail, they are extremely important.
What enables buildpacks to go unnoticed is auto-detection, which happens when a platform sequentially
tests groups of buildpacks against your app’s source code. The first group that deems itself fit for your source code
will become the selected set of buildpacks for your app. Detection criteria is specific to each buildpack – for
instance, an NPM buildpack might look for a
package.json, and a Go buildpack might look for Go source files.
Let’s see auto-detection in action by running
pack build against a simple Java application.
packfor the journey
Start by installing Docker and
Next, clone or download this simple Java app source code to a location of your choosing.
Now run the following commands in a shell:
$ cd path/to/sample-java-app $ pack build myapp
If this is your first time running
pack, you might see a message about selecting a default builder (essentially, an image containing buildpacks). Simply choose either builder presented by running
pack set-default-builder <builder>, then run
pack build myappagain.
That’s it. You’ve now got a runnable app image called
myapp available on your local Docker daemon.
We did say this was a brief journey after all! Take note that your app was built without needing to install
a JDK, run Maven, or otherwise configure a build environment.
pack and the buildpacks took care of that for you.
To test out your new app image locally, you can run it with Docker:
$ docker run --rm -p 8080:8080 myapp
localhost:8080 in your favorite browser and take a minute to admire your handiwork.
pack uses Cloud Native Buildpacks to help you easily create OCI images that you can run just about anywhere. Try
deploying your new image to your favorite cloud!
In case you need it,
pack buildhas a handy flag called
--publishthat will publish your app image to a Docker registry after building it.