Discovery buildpack

Buildpack that prints out arguments being passed between bin/detect, bin/build, and the resulting Docker image.

• https://buildpacks.io/docs/create-buildpack/building-blocks-cnb/
• https://github.com/buildpack/spec/blob/master/buildpack.md

NOTE: This buildpack was created with pack from source, just prior to v0.4.0 release during August 2019. If the outputs or behavior changes, please let me know and I'll update the README or buildpack scripts.

NOTE: The builder.toml explicitly uses lifecycle 0.4.0. If there is a newer lifecycle version available, this buildpack may need updating before bumping the builder.toml.

Playtime with buildpack

pack build discovery-app --buildpack . --path fixtures/ruby-sample-app

To see inside the runtime Docker image:

docker run -ti discovery-app bash

The original fixtures/ruby-sample-app is placed in the working directory at /workspace:

$ pwd
/workspace
$ ls
Gemfile  Gemfile.lock  app.rb  vendor

A metadata file is created from the buildpacks detected and used to create the application:

$ cat /layers/config/metadata.toml
processes = []
buildpacks = ["com.starkandwayne.buildpacks.discovery"]

[[processes]]
  type = "web"
  command = "nc-webapp"

[bom]
  [bom.discovery]
    message = "hello"
    version = "1.2.3"

The layers added by the buildpacks are at /layers:

$ ls -alR /layers/com*/
/layers/com.starkandwayne.buildpacks.discovery/:
total 12
drwxr-xr-x 3 vcap vcap 4096 Jan  1  1980 .
drwxr-xr-x 1 vcap vcap 4096 Jan  1  1980 ..
drwxr-xr-x 2 vcap vcap 4096 Jan  1  1980 discovery-launch-true

/layers/com.starkandwayne.buildpacks.discovery/discovery-launch-true:
total 12
drwxr-xr-x 3 vcap vcap 4096 Jan  1  1980 .
drwxr-xr-x 3 vcap vcap 4096 Jan  1  1980 ..
drwxr-xr-x 2 vcap vcap 4096 Jan  1  1980 bin
-rw-r--r-- 1 vcap vcap    0 Jan  1  1980 some-file

/layers/com.starkandwayne.buildpacks.discovery/discovery-launch-true/bin:
total 16
drwxr-xr-x 2 vcap vcap 4096 Jan  1  1980 .
drwxr-xr-x 3 vcap vcap 4096 Jan  1  1980 ..
-rwxr-xr-x 1 vcap vcap   32 Jan  1  1980 hello
-rwxr-xr-x 1 vcap vcap   27 Jan  1  1980 nc-webapp

The hello and nc-webapp executables are automatically added into the $PATH:

$ hello
hello world

$ echo $PATH
/layers/com.starkandwayne.buildpacks.discovery/discovery-launch-true/bin:...

Run the tiny nc-based web app explicitly:

$ docker run -ti -p 8080:8080 --env PORT=8080 discovery-app nc-webapp
Listening on [0.0.0.0] (family 0, port 8080)

But the nc-webapp is also described by bin/build as a launch process, so it is automatically run as the default behavior of the Docker image:

$ docker run -ti -p 8080:8080 --env PORT=8080 discovery-app
Listening on [0.0.0.0] (family 0, port 8080)

Playtime with builder containing buildpack

pack create-builder starkandwayne/discovery-cnb -b builder.toml

The output may look like:

Creating builder starkandwayne/discovery-builder from build-image cloudfoundry/cnb-build:cflinuxfs3
Downloading from "https://github.com/buildpack/lifecycle/releases/download/v0.3.0/lifecycle-v0.3.0+linux.x86-64.tgz"
Successfully created builder image starkandwayne/discovery-builder
Tip: Run pack build <image-name> --builder starkandwayne/discovery-builder to use this builder

Now we can try applying the buildpack automatically from within our custom builder:

pack build discovery-app --builder starkandwayne/discovery-builder --path fixtures/ruby-sample-app

The output shows that our buildpack is successfully detected and built into the final application Docker image:

Selected run image cloudfoundry/cnb-run:cflinuxfs3
Pulling image cloudfoundry/cnb-run:cflinuxfs3
cflinuxfs3: Pulling from cloudfoundry/cnb-run
Digest: sha256:d5ac181ce8f1f3e9411a693d43b89508dc00bfa3509979dacf8c6ae00911f7cb
Status: Image is up to date for cloudfoundry/cnb-run:cflinuxfs3
Using build cache volume pack-cache-7296676022e3.build
Executing lifecycle version 0.3.0
===> DETECTING
[detector] Trying group 1 out of 1 with 1 buildpacks...
[detector] ======== Output: Discovery Buildpack ========
[detector] $1 platform: /platform
[detector] /platform/:
[detector] total 12
[detector] drwxr-xr-x 1 root root 4096 Aug 28 23:13 .
[detector] drwxr-xr-x 1 root root 4096 Aug 28 23:13 ..
[detector] drwxr-xr-x 1 root root 4096 Aug 28 23:13 env
[detector]
[detector] /platform/env:
[detector] total 8
[detector] drwxr-xr-x 1 root root 4096 Aug 28 23:13 .
[detector] drwxr-xr-x 1 root root 4096 Aug 28 23:13 ..
[detector]
[detector] $2 plan: /tmp/0.0.1.plan.966117460/plan.toml
[detector] -rwxr-xr-x 1 vcap vcap 53 Aug 28 23:13 /tmp/0.0.1.plan.966117460/plan.toml
[detector] ======== Results ========
[detector] pass: Discovery Buildpack
===> RESTORING
===> ANALYZING
[analyzer] Analyzing image '229b154bb00578763c0e4717d93b5089f6537412ae62b0ebab159bfd3580931d'
[analyzer] Writing metadata for uncached layer 'com.starkandwayne.buildpacks.discovery:discovery-launch-true'
===> BUILDING
[builder] ---> Discovery Buildpack
[builder] $1 layers: /layers/com.starkandwayne.buildpacks.discovery
[builder] /layers/com.starkandwayne.buildpacks.discovery:
[builder] total 12
[builder] drwxr-xr-x 2 vcap vcap 4096 Aug 28 23:13 .
[builder] drwxr-xr-x 3 vcap vcap 4096 Aug 28 23:13 ..
[builder] -rw-r--r-- 1 vcap vcap   42 Aug 28 23:13 discovery-launch-true.toml
[builder]
[builder] $2 platform: /platform
[builder] /platform:
[builder] total 12
[builder] drwxr-xr-x 1 root root 4096 Aug 28 23:13 .
[builder] drwxr-xr-x 1 root root 4096 Aug 28 23:13 ..
[builder] drwxr-xr-x 1 root root 4096 Aug 28 23:13 env
[builder]
[builder] /platform/env:
[builder] total 8
[builder] drwxr-xr-x 1 root root 4096 Aug 28 23:13 .
[builder] drwxr-xr-x 1 root root 4096 Aug 28 23:13 ..
[builder]
[builder] $3 plan: /tmp/plan.833650968/com.starkandwayne.buildpacks.discovery/plan.toml
[builder] -rwxr-xr-x 1 vcap vcap 0 Aug 28 23:13 /tmp/plan.833650968/com.starkandwayne.buildpacks.discovery/plan.toml
[builder] [[entries]]
[builder]   name = "discovery"
[builder]   version = "1.2.3"
[builder]   [entries.metadata]
[builder]     message = "hello"
[builder]
[builder] STDIN:
[builder]
[builder] ---> Make some layers
[builder] ---> create bin/hello
[builder] ---> create tiny webapp with nc
===> EXPORTING
[exporter] Reusing layers from image with id '229b154bb00578763c0e4717d93b5089f6537412ae62b0ebab159bfd3580931d'
[exporter] Reusing layer 'app' with SHA sha256:4485fd00798ca2d1253b5ba46d4596acaf851d9d93de119efa7ce5de84243b06
[exporter] Reusing layer 'config' with SHA sha256:60c732e5c5769263b6f67fcd4530674301d425cbdd8a16b48b7b91851fbf5a66
[exporter] Reusing layer 'launcher' with SHA sha256:c8a8ddb80dd9923057bd12f9f69c6b093925a8925f3c37550a88b90f02699aa9
[exporter] Reusing layer 'com.starkandwayne.buildpacks.discovery:discovery-launch-true' with SHA sha256:1b1c0bd2e64912ea2731debd41c3bbaf2b918a0cb167b33a2ed4a99d8344aafc
[exporter] *** Images:
[exporter]       index.docker.io/library/discovery-app:latest - succeeded
[exporter]
[exporter] *** Image ID: 73e6e712829833ca914ed6685f86d253367e3945b0f0cbc7759b474f23d6e420
===> CACHING
Successfully built image discovery-app

kpack

To install the discovery-builder builder into kpack, that contains this buildpack, use:

kubectl apply -f kpack-builder.yml

To apply the buildpack, via the builder, to an example project (this repo) apply the sample file. First update it for your own spec.tag and spec.serviceAccount.

kubectl apply -f kpack-fixture-app-build-from-git.yml

It will take a while for the first build to kick off, as Kubernetes needs to download the new starkandwayne/discover-builder image from Docker Hub registry.

To watch the buildpack lifecycle use kpack's logs CLI:

logs -image discovery-cnb-fixture-app

Run the published image locally:

docker run -ti -p 8080:8080 --env PORT=8080 starkandwayne/discovery-cnb-fixture-app

Subsequent changes to this Git repo should automatically trigger kpack to rebuild the Docker image.