In the past, I've worked with buildpacks through my time using Cloud Foundry. Cloud Foundry has first class support for buildpacks, which allows you to push code and let the buildpack handle the messy parts of actually running your code. Things like installing a language runtime, installing servers, etc...
Recently the buildpacks world has expanded with the
CNCF's acceptance of the Cloud Native Buildpacks project into the CNCF sandbox (sometimes called v3 buildpacks). In addition to an
excellent and easily readable spec, this work brings us the
`pack` CLI tool, which allows you to run Cloud Native Buildpacks on your local PC and easily deploy the output, which is an OCI image, to Docker or anywhere else you can run an OCI image.
In this post, I'm going to walk through some basics and show you how to get started with
`pack`, build some image and run them.
Getting Started
To get started you need to install Docker. The
Community Edition works fine. Follow the previous link to get that installed, if you don't have it already.
Then install the
`pack` CLI. You can download
`pack` from its Github project
here. At the time of writing, I'm using the 0.0.9 release.
To download the tar or zip, extract the `pack` binary and put it somewhere on your PATH. On Mac/Linux,
`/usr/local/bin` is a good place. Once installed, you should be able to run
`pack version` and see
`v0.0.9 (git sha: a1a1a0eef63bd09136ab76663bdbc3b0ab3a4931)`.
Hello World
To get a basic app going, we need to do one more thing first. Obtain some buildpacks to use. So run
`git clone https://github.com/buildpack/samples`, which is a repo that has a couple very basic sample buildpacks.
Sidebar. At the time of writing, the sample buildpack we're using has an error with it's metadata. You may not need to do this in the future. Edit
`samples/hello-world-buildpack/buildpack.toml` and put in the following:
[buildpack]
id = "io.buildpacks.samples.buildpack.hello-world"
version = "0.0.1"
name = "Hello World Buildpack"
[[stacks]]
id = "io.buildpacks.stacks.bionic"
Now that we have buildpacks, we need an app to run. We'll create that now. Run
`mkdir hello-world` and then
`cd hello-world`. In that folder create
`app.sh` and put the following in that file.
#!/bin/bash
while [ 1 -eq 1 ]; do
echo "Hello World!"
sleep 5
done
Last step, run
`chmod 755 app.sh` to make it executable.
At this point, we now have a buildpack to use and our application code. It's time to run
`pack` and make an image.
From our application directory run
`pack build --buildpack $(cd ..; pwd)/samples/hello-world-buildpack/ hello-world-app` or replace
`$(cd ..; pwd)/samples/hello-world-buildpack/` with the full path to the sample repo you cloned above. This will create an image called
`hello-world-app` using the
`hello-world-buildpack`, which does nothing (it's a no-op). The output should look something like this.
$ pack build --buildpack $(cd ..; pwd)/samples/hello-world-buildpack/ hello-world-app
Defaulting app directory to current working directory /Users/dmikusa/Downloads/hello-world (use --path to override)
Using default builder image packs/samples:v3alpha2
Pulling builder image packs/samples:v3alpha2 (use --no-pull flag to skip this step)
Selected run image packs/run:v3alpha2 from stack io.buildpacks.stacks.bionic
Pulling run image packs/run:v3alpha2 (use --no-pull flag to skip this step)
Using cache volume pack-cache-153f385b25c48f5d30ee0544d75bee63
===> DETECTING
Using manually-provided group
[detector] 2019/02/17 21:09:40 Trying group of 1...
[detector] 2019/02/17 21:09:41 ======== Results ========
[detector] 2019/02/17 21:09:41 Hello World Buildpack: pass
===> ANALYZING
Reading information from previous image for possible re-use
[analyzer] 2019/02/17 21:09:42 WARNING: image 'hello-world-app' not found or requires authentication to access
[analyzer] 2019/02/17 21:09:42 removing cached layers for buildpack 'config' not in group
===> BUILDING
[builder] ---> Hello World buildpack
[builder] env_dir: /platform/env
[builder] plan_path: /tmp/plan.333599924/io.buildpacks.samples.buildpack.hello-world/plan.toml
[builder] layers_dir: /workspace/io.buildpacks.samples.buildpack.hello-world
[builder] ---> Done
===> EXPORTING
[exporter] 2019/02/17 21:09:48 adding layer 'app' with diffID 'sha256:361cdaf2662ea41f08da0204a4c0393beb629cff85df2b3d650ed7423dc188f2'
[exporter] 2019/02/17 21:09:48 adding layer 'config' with diffID 'sha256:ab046f0bf0b24db6ae8f59e437cc570925e451cb60ae714fcb125ab4095dd9bb'
[exporter] 2019/02/17 21:09:49 adding layer 'launcher' with diffID 'sha256:d77dc7ed6207d6bb9c389aa5f087ea7fffea9238e2de84b03f8b3c1152e1e58f'
[exporter] 2019/02/17 21:09:49 setting metadata label 'io.buildpacks.lifecycle.metadata'
[exporter] 2019/02/17 21:09:49 setting env var 'PACK_LAYERS_DIR=/workspace'
[exporter] 2019/02/17 21:09:49 setting env var 'PACK_APP_DIR=/workspace/app'
[exporter] 2019/02/17 21:09:49 setting entrypoint '/lifecycle/launcher'
[exporter] 2019/02/17 21:09:49 setting empty cmd
[exporter] 2019/02/17 21:09:49 writing image
[exporter] 2019/02/17 21:09:49
[exporter] *** Image: hello-world-app@9b265f861002fa1018d48577fb2f78c4e32b58f72f81c8ef9f6692d2040b4d60
Successfully built image hello-world-app
The interesting bits for now are DETECTING, where the buildpack's detection script runs. This buildpack doesn't do anything but we can see it's marked as "pass" which means the buildpack's build script will get a chance to run. Down below you can see that happening under BUILDING. This again does nothing, but echo a few directories where files reside during build. Legit buildpacks would use detect to determine when they should/shouldn't run and build to install things like runtimes, servers and all the stuff necessary to run your apps.
The output from above is a image that you can run. If you execute `docker images`, you'll see `hello-world-app` listed.
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-world-app latest 9b265f861002 6 minutes ago 164MB
You can then run it with
`docker run -it --name=hello hello-world-app bash app.sh`. The app will run forever printing "Hello World!". Run
`docker stop hello` to stop the app.
Hello World++
To spice things up just a little bit and show what it's like to deploy changes to our app, let's edit our
`app.sh` script. Set it to this.
#!/bin/bash
while [ 1 -eq 1 ]; do
if [ "$NAME" == "" ]; then
echo "Hello World!"
else
echo "Hello $NAME!"
fi
sleep 5
done
This will allow us to provide a name to print. Run
`pack build --buildpack $(cd ..; pwd)/samples/hello-world-buildpack/ hello-world-app` again. This will create a new image with our updated app
.
Side note, if you run
`docker images` you'll see that the old image is no longer used and can be removed at your leisure.
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-world-app latest 793b5e60b5ad 9 seconds ago 164MB
9b265f861002 20 minutes ago 164MB
To run the updated app image, you can use the same command
`docker run -it --name=hello hello-world-app bash app.sh` and you'll see the same output. However, if you run
`docker run -it -e NAME=Daniel --name=hello hello-world-app bash app.sh` you'll see our enhancement.
$ docker run -it -e NAME=Daniel --name=hello hello-world-app bash app.sh
Hello Daniel!
...
We use Docker's ability to set environment variables to inject some data into our application. More importantly though, you can see that pushing updates and changes is the same process as you used before which makes integrating into build systems and CI/CD systems simple.
Summary
I hope you find getting started is easy. Once you get Docker & pack installed it's one command to stamp out an image using a buildpack and our application. Right now, that buildpack isn't doing anything, so it's not the best demonstration of why you'd want use buildpacks or the full power of them, but I hope this is enough to get you thinking about how this can integrate into your build flows, maybe your CI/CD system and how it can work for you.
My next post will be more practical. It'll dig into some actual buildpacks and show how you can use them to make images for actual applications, and I hope this will better showcase why you would want to use buildpacks.
