Java buildpack Client

Prototype of a simple buildpack (https://buildpacks.io/) client for java.

This project represents a simple implementation of the buildpack platform spec, and can be used to build projects using specified buildpacks.

This project implements up to version 0.10 of the buildpack platform spec, and should work with builders requesting from 0.4 through to 0.10. 0.12 is available but experimental.

A fluent interface is provided to allow creation & configuration of the build to be performed.

A very simple build can be performed with as little as.

int exitCode = BuildConfig.builder()
                           .withOutputImage(new ImageReference("test/testimage:latest"))
                           .addNewFileContentApplication(new File("/home/user/java-project"))
                           .build()
                           .getExitCode();

This will use the default builder image from (https://paketo.io) to handle the build of the project in the /home/user/java-project folder. The resulting image will be stored in the local docker daemon as test/testimage:latest.

Overview

The BuildpackConfig offers other configuration methods to customise behavior.

• run/build/output Image can be specified
• docker can be configured with..
  • pull timeout
  • host
  • network
  • docker socket path
  • if Daemon should be used or not. (If yes, docker socket is mounted into build container so buildpack can make use of daemon directly, if no, then docker will read/create output images with remote registry directly. Note that daemon is still used to run the various build containers, just that the containers do not themselves have access to the daemon.)
• caches (launch/build/kaniko) can be configured with..
  • cache volume name. (if omitted, a randomly generated name is used)
  • cache delete after build. (if yes, cache volume will be removed after build exits, defaults to TRUE)
• logging from the build containers can be customized..
  • log level, can be info, warn, debug. Affects the amount of verbosity from the lifecycle during build.
  • logger instance, system logger (to sysout/syserr) and slf4j loggers are supplied.
• platform aspects can be customized..
  • platform level can be forced to a version, by default platform level is derived from the intersection of builder/lifecycle and platform supported versions.
  • environment vars can be set that will be accessible during the build as platform env vars.
  • the builder can be 'trusted'. This means the creator lifecycle is used, where all phases happen within a single container, faster, but does not support extensions, and can expose some lifecycle phases to credentials that may be otherwise protected.
  • lifecycle image can be specified. If set, the lifecycle from the specified image will be used instead of the one within the builder image. Allows for easy testing with newer lifecycles.

A variety of methods are supported for adding content to be build, content is combined in the order passed, allowing for sparse source directories, or multiple project dirs to be combined.

• File/Directory, with prefix. Eg, take this directory /home/fish/wibble, and make it appear in the application content as /prodcode
• String Content, with path. Eg, take this String content "FISH" and make it appear in the application content as /prodcode/fish.txt
• InputStream Content, with path. Similar to String, except with data pulled from an InputStream.
• ContainerEntry interface, for custom integration.

Build/RunImages will be pulled as required.

The builder will use docker via the DOCKER_HOST env var, if configured, or via the platform appropriate docker socket if not. Alternatively, dockerHost can be directly configured on the builder itself. If the docker host starts with unix:// the path to the docker socket is extracted and used during the build phase. If unset, this defaults to /var/run/docker/sock

How To:

Want to try out this project? The packages/api are not fixed in stone yet, so be aware! But here are the basic steps to get you up and running.

1. Add this project as a dependency.. (use the latest version instead of XXX)

       <dependency>
           <groupId>dev.snowdrop</groupId>
           <artifactId>buildpack-client</artifactId>
           <version>0.0.9</version>
       </dependency> 

2. Instantiate a BuildConfig

   BuildConfig bc = BuildConfig.builder();

3. Define the content to be built..

   bc = bc.addNewFileContentApplication(new File("/path/to/the/project/to/build));

4. Configure the name/tags for the image to create

   bc = bc.withOutputImage(new ImageReference("myorg/myimage:mytag"));

5. Invoke the build

   bc.build();

6. Retrieve the build exit code

   bc.getExitCode();

Or combine all the above steps into a single callchain.

int exitCode = BuildConfig.builder()
                           .withOutputImage(new ImageReference("test/testimage:latest"))
                           .addNewFileContentApplication(new File("/home/user/java-project"))
                           .build()
                           .getExitCode();

There are many more ways to customize & configure the BuildConfig, take a look at the interface to see everything thats currently possible.

A demo project has been created to allow easy exploration of uses of BuildConfig here :-)

Most likely if you are using this to integrate to existing tooling, you will want to supply a custom LogReader to receive the messages output by the Build Containers during the build. You may also want to associate cache names to a project, to enable faster rebuilds for a given project. Note that if you wish caches to survive beyond a build, you should set deleteCacheAfterBuild to false for each cache. Eg.

int exitCode = BuildConfig.builder()
                          .withNewBuildCacheConfig()
                              .withCacheVolumeName("my-project-specific-cache-name")
                              .withDeleteCacheAfterBuild(true)
                              .and()
                          .withOutputImage(new ImageReference("test/testimage:latest"))
                          .addNewFileContentApplication(new File("/home/user/java-project"))
                          .build()
                          .getExitCode();

Logging

Output from the Buildpack execution is available via the dev.snowdrop.buildpack.Logger interface, which can be optionally be passed using the builder. At the moment two kinds of logger are supported:

• SystemLogger (default)
• Slf4jLogger

Both can be configured using the builder:

int exitCode = BuildConfig.builder()
                          .withNewLogConfig()
                              .withLogger(new SystemLogger())
                              .withLogLevel("debug")
                              .and()
                          .withOutputImage(new ImageReference("test/testimage:latest"))
                          .addNewFileContentApplication(new File("/home/user/java-project"))
                          .build()
                          .getExitCode();

or

int exitCode = BuildConfig.builder()
                          .withNewLogConfig()
                              .withLogger(new Slf4jLogger())
                              .withLogLevel("debug")
                              .and()
                          .withOutputImage(new ImageReference("test/testimage:latest"))
                          .addNewFileContentApplication(new File("/home/user/java-project"))
                          .build()
                          .getExitCode();

Inline Logger configuration

The builder DSL supports inlining Logger configuration:

int exitCode = BuildConfig.builder()
                          .withNewLogConfig()
                              .withNewSystemLogger(false)
                              .withLogLevel("debug")
                              .and()
                          .withOutputImage(new ImageReference("test/testimage:latest"))
                          .addNewFileContentApplication(new File("/home/user/java-project"))
                          .build()
                          .getExitCode();

The above statement configures system logger with disabled ansi colors.

Similarly, with Slf4jLogger one can inline the name of the logger:

int exitCode = BuildConfig.builder()
                          .withNewLogConfig()
                             .withNewSlf4jLogger(MyApp.class.getCanonicalName())
                             .withLogLevel("debug")
                             .and()
                          .withOutputImage(new ImageReference("test/testimage:latest"))
                          .addNewFileContentApplication(new File("/home/user/java-project"))
                          .build()
                          .getExitCode();

Error Handling

If the build fails for any reason, a BuildpackException will be thrown, this is a RuntimeException, so does not need an explicit catch block. There are many many ways in which a build can fail, from something environmental, like docker being unavailable, to build related issues, like the chosen builder image requiring a platformlevel not implemented by this library.

Using the buildpack client with jbang

The easiest way to invoke arbitrary java code, without much hassle is by using jbang.

So, you can drop the following file in your project: (swap XXX for latest release of buildpack-client)

///usr/bin/env jbang "$0" "$@" ; exit $?

//DEPS dev.snowdrop:buildpack-client:0.0.9}
import static java.lang.System.*;

import java.io.File;
import dev.snowdrop.buildpack.*;

public class pack {

    public static void main(String... args) {
        int exitCode = BuildConfig.builder()
                                .withOutputImage(new ImageReference("test/testimage:latest"))
                                .addNewFileContentApplication(new File("/home/user/java-project"))
                                .build()
                                .getExitCode();
        System.exit(exitCode);
    }
}

... and just run it using:

./pack.java

The samples use jbang too, but allow the version of the library to be set via an env var for use in our tests! samples.

FAQ:

Will this work with Podman?:

Yes, tested with Podman 4.7.0 on Fedora, rootless and rootful.

Does this work on Windows?:

Yes.. it's supposed to! Tested with Win10 + Docker on WSL2

Does this work on Linux?:

Yes.. Tested with Ubuntu & Fedora with Docker

Can I supply buildpacks/extensions to add to a builder like pack?:

The code is structured to allow for this, but the feature is not exposed via the builder api, as using additional buildpacks/extensions requires updating order.toml in the base builder, and that would require additional config to either override, or specify the behavior for manipulating the toml. If you are interested in this kind of functionality, raise an Issue so I can better understand the use case, or send a PR!