Bhojpur Ara - Automated Resource Assembly

The Bhojpur Ara is a software developer's tool used for automated resource assembly within the Bhojpur.NET Platform ecosystem. It assembles platform aware custom applications and/or services. It is an experimental Docker/OCI image builder. Its goal is to build independent layers, where a change to one layer does not invalidate the ones sitting "above" it.

How does it work?

The Bhojpur Ara software has three main capabilities.

1. build independent layer chunks: in a Bhojpur Ara project there's a chunks/ folder which contains individual Dockerfiles (e.g. chunks/something/Dockerfile). These chunk images are built independently of each other. All of them share the same base image using a special build argument ${base}. The Bhojpur Ara can build the base image (built from base/Dockerfile), as well as the chunk images. After each chunk image build, the Bhojpur Ara will remove the base image layer from that image, leaving just the layers that were produced by the chunk Dockerfile.
2. merge layers into one image: the Bhojpur Ara can merge multiple OCI images/chunks (not just those built using the Bhopjur Ara) by building a new manifest and image config that pulls the layers/DiffIDs from the individual chunks and the base image they were built from.
3. run tests against images: to ensure that an image is capable of what we think it should be - especially after merging - the Bhojpur Ara supports simple tests and assertions that run against Docker images.

Would I want to use this?

No. For example, if you're packing your custom applications or services, you're probably better of with a regular Docker image build and well established means for optimizing that one (think multi-stage builds, proper layer ordering).

If however you are building custom images, which consist of a lot of independent concerns, i.e. chunks that can be strictly separated, then this might be for you. For example, if you're building a custom image that serves as a collection of tools, the layer hierarchy imposed by regular builds doesn't fit so well.

Limitations and caveats

• build args are not supported at the moment
• there are virtually no tests covering this so things might just break
• consider this alpha-level software

Requirements

• Install Go 1.18.1 programming language

sudo wget https://go.dev/dl/go1.18.1.linux-amd64.tar.gz
sudo tar -C /usr/local -xzf ~/go1.18.1.linux-amd64.tar.gz
sudo sh -c 'echo "export PATH=$PATH:/usr/local/go/bin" >> /etc/profile'

Now, logout from the terminal session and login again

go version

Hopefully, you would see something like go version go1.18 linux/amd64

• Install and run Docker BuildKit - currently 0.9.3 - in the background. It helps in building software applications using Docker container runtime.

Pull and run a Docker registry.

NOTE: if you are running it in the Bhojpur.NET Platform, this is done for you already!

sudo su -c "cd /usr; curl -L https://github.com/moby/buildkit/releases/download/v0.9.3/buildkit-v0.9.3.linux-amd64.tar.gz | tar xvz"
$ docker run -p 5000:5000 --name registry --rm registry:2

Build the Bhojpur Ara suitable for your environment

Firstly, clone this Git repository in a preferred work folder, then issue the following commands

cd ara
go mod tidy
go get
go build -o bin/ara main.go
go build -o bin/arautl main-util.go

If the build was successful, then you should get ara executable image in a local folder.

Getting started

# start a new project
ara project init

# add your first chunk
ara project init helloworld
echo hello world > chunks/helloworld/hello.txt
echo "COPY hello.txt /" >> chunks/helloworld/Dockerfile 

# add another chunk, just for fun
ara project init anotherchunk
echo some other chunk > chunks/anotherchunk/message.txt
echo "COPY message.txt /" >> chunks/anotherchunk/Dockerfile

# register a combination which takes in all the chunks
ara project add-combination full helloworld anotherchunk

# build the chunks
ara build us-west2-docker.pkg.dev/some-project/ara-test

# build all combinations
ara combine us-west2-docker.pkg.dev/some-project/ara-test --all

Simple Usage

To learn how to use the Bhojpur Ara

Initialization

$ ara project init
Starts a new Bhojpur Ara project

Usage:
  ara project init [chunk] [flags]

Flags:
  -h, --help   help for init

Global Flags:
      --addr string      address of buildkitd (default "unix:///run/buildkit/buildkitd.sock")
      --context string   context path (default "/platform/application-images")
  -v, --verbose          enable verbose logging

Starts a new Bhojpur Ara project. If you don't know where to start, this is the place.

Building

$ ara build --help
Builds a Docker image with independent layers

Usage:
  ara build <target-ref> [flags]

Flags:
      --chunked-without-hash   disable hash qualification for chunked image
  -h, --help                   help for build
      --no-cache               disables the buildkit build cache
      --plain-output           produce plain output

Global Flags:
      --addr string      address of buildkitd (default "unix:///run/buildkit/buildkitd.sock")
      --context string   context path (default "/platform/application-images")
  -v, --verbose          enable verbose logging

The Bhojpur Ara can build regular Docker files much like docker build would. build will build all images found under chunks/.

The Bhojpur Ara cannot reproducibly build layers but can only re-use previously built ones. To ensure reusable layers and maximize Docker cache hits, Ara itself caches the layers it builds in a Docker registry.

Combining

$ ara combine --help
Combines previously built chunks into a single image

Usage:
  ara combine <target-ref> [flags]

Flags:
      --all                  build all combinations
      --build-ref string     use a different build-ref than the target-ref
      --chunks string        combine a set of chunks - format is name=chk1,chk2,chkN
      --combination string   build a specific combination
  -h, --help                 help for combine
      --no-test              disables the tests

Global Flags:
      --addr string      address of buildkitd (default "unix:///run/buildkit/buildkitd.sock")
      --context string   context path (default "/platform/application-images")
  -v, --verbose          enable verbose logging

The Bhojpur Ara can combine previously built chunks into a single image. For example: ara combine some.registry.com/ara --chunks foo=chunk1,chunk2 will combine base, chunk1 and chunk2 into an image called some.registry.com/ara:foo.

One can pre-register such chunk combinations using ara project add-combination.

The ara.yaml file specifies the list of available combinations. Those combinations can also reference each other:

combiner:
  combinations:
  - name: minimal
    chunks:
    - golang
  - name: some-more
    ref:
    - minimal
    chunks:
    - node

Testing layers and merged images

During a Bhojpur Ara build, one can test the individual layers and the final image.

During the build, the Bhojpur Ara will execute the layer tests for each individual layer, as well as the final image. This makes finding and debugging issues created by the layer merge process tractable.

Each chunk gets its own set of tests found under tests/chunk.yaml.

For example:

- desc: "it should demonstrate tests"
  command: ["echo", "hello world"]
  assert:
  - status == 0
  - stdout.indexOf("hello") != -1
  - stderr.length == 0
- desc: "it should handle exit codes"
  command: ["sh", "-c", "exit 1"]
  assert:
  - status == 1
- desc: "it should have environment variables"
  command: ["sh", "-c", "echo $MESSAGE"]
  env:
  - MESSAGE=foobar
  assert:
  - stdout.trim() == "foobar"

Assertions

All test assertions are written in ES5 Javascript. Three variables are available in an assertion:

• stdout contains the standard output produced by the command
• stderr contains the standard error output produced by the command
• status contains the exit code of the command/container.

The assertion itself must evaluate to a boolean value, otherwise the test fails.

Testing approach

While the test runner is standalone, the linux+amd64 version is embedded into the Bhojpur Ara binary using go.rice and go generate - see build.sh.

TODO: use go:embed?

NOTE that if you make changes to code in the test runner you will need to re-embed the runner into the binary in order to use it via Bhojpur Ara.

go generate ./...

The test runner binary is extracted and copied to the generated image, where it is run using an encoded JSON version of the test specification - see container.go. The exit code, stdout & stderr are captured and returned for evaluation against the assertions in the test specification.

While of limited practical use, it is possible to run the test runner standalone using a base64-encoded JSON blob as a parameter:

$ go run pkg/test/runner/main.go eyJEZXNjIjoiaXQgc2hvdWxkIGhhdmUgR28gaW4gdmVyc2lvbiAxLjEzIiwiU2tpcCI6ZmFsc2UsIlVzZXIiOiIiLCJDb21tYW5kIjpbImdvIiwidmVyc2lvbiJdLCJFbnRyeXBvaW50IjpudWxsLCJFbnYiOm51bGwsIkFzc2VydGlvbnMiOlsic3Rkb3V0LmluZGV4T2YoXCJnbzEuMTFcIikgIT0gLTEiXX0=
{"Stdout":"Z28gdmVyc2lvbiBnbzEuMTYuNCBsaW51eC9hbWQ2NAo=","Stderr":"","StatusCode":0}

The stdout/err are returned as base64-encoded values. They can be extracted using jq e.g.:

go run pkg/test/runner/main.go eyJEZXNjIjoiaXQgc2hvdWxkIGhhdmUgR28gaW4gdmVyc2lvbiAxLjEzIiwiU2tpcCI6ZmFsc2UsIlVzZXIiOiIiLCJDb21tYW5kIjpbImdvIiwidmVyc2lvbiJdLCJFbnRyeXBvaW50IjpudWxsLCJFbnYiOm51bGwsIkFzc2VydGlvbnMiOlsic3Rkb3V0LmluZGV4T2YoXCJnbzEuMTFcIikgIT0gLTEiXX0= | jq -r '.Stdout | @base64d'
$ go version go1.18.1 linux/amd64

Integration tests

There is an integration test for the build command in pkg/ara/build_test.go - TestProjectChunk_test_integration and a shell script to run it.

The integration test does an end-to-end check along with editing a test and re-running to ensure only the test image is updated.

It requires a running BuildkitD instance at unix:///run/buildkit/buildkitd.sock and a Docker registry on 127.0.0.1:5000 (i.e. as this workspace is setup on startup).

Override the env vars BUILDKIT_ADDR and TARGET_REF as required prior to running in a different environment.

./integration_tests.sh