Java Distribution Gradle Plugin

Similar to the standard application plugin, this plugin facilitates packaging Gradle projects for easy distribution and execution. This distribution chooses different packaging conventions that attempt to split immutable files from mutable state and configuration.

In particular, this plugin packages a project into a common deployment structure with a simple start script, daemonizing script, and, a manifest describing the content of the package. The package will follow this structure:

[service-name]-[service-version]/
    deployment/
        manifest.yml                      # simple package manifest
    service/
        bin/
            [service-name]                # Bash start script
            [service-name].bat            # Windows start script
            init.sh                       # daemonizing script
            darwin-amd64/go-java-launcher # Native Java launcher binary (MacOS)
            linux-amd64/go-java-launcher  # Native Java launcher binary (Linux)
            launcher-static.yml           # generated configuration for go-java-launcher
            launcher-check.yml            # generated configuration for check.sh go-java-launcher
        lib/
            [jars]
        monitoring/
            bin/ 
                check.sh                  # monitoring script
    var/                                  # application configuration and data

The service/bin/ directory contains both Gradle-generated launcher scripts ([service-name] and [service-name].bat) and go-java-launcher launcher binaries.

Packages are produced as gzipped tar named [service-name]-[project-version].tgz.

Usage

Apply the plugin using standard Gradle convention:

plugins {
    id 'com.palantir.java-distribution'
}

Set the service name, main class, and optionally the arguments to pass to the program for a default run configuration:

distribution {
    serviceName 'my-service'
    mainClass 'com.palantir.foo.bar.MyServiceMainClass'
    args 'server', 'var/conf/my-service.yml'
}

The distribution block offers the following options:

• serviceName the name of this service, used to construct the final artifact's file name.
• mainClass class containing the entry point to start the program.
• (optional) args a list of arguments to supply when running start.
• (optional) checkArgs a list of arguments to supply to the monitoring script, if omitted, no monitoring script will be generated.
• (optional) defaultJvmOpts a list of default JVM options to set on the program.
• (optional) enableManifestClasspath a boolean flag; if set to true, then the explicit Java classpath is omitted from the generated Windows start script and instead inferred from a JAR file whose MANIFEST contains the classpath entries.
• (optional) excludeFromVar a list of directories (relative to var) to exclude in addition to log and run (which are always excluded).
• (optional) javaHome a fixed override for the JAVA_HOME environment variable that will be applied when init.sh is run.

JVM Options

The list of JVM options passed to the Java processes launched through a package's start-up scripts is obtained by concatenating the following list of hard-coded required options and the list of options specified in distribution.defaultJvmOpts:

Hard-coded required JVM options:

• -Djava.security.egd=file:/dev/./urandom: urandom is the preferred source of cryptographic randomness on modern Linux systems. Note that some Java implementations override /dev/urandom internally; we thus set it to /dev/./urandom.
• -Djava.io.tmpdir=var/data/tmp: Allocates temporary files inside the application installation folder rather than on /tmp; the latter is often space-constrained on cloud hosts.
• -XX:+PerfDisableSharedMem: Avoids long garbage collection pauses. As a side-effect, some Java debug tools (e.g., jps, jstat) are unavailable for processes launched through the startup scripts.

The go-java-launcher and init.sh launchers additionally append the list of JVM options specified in the var/conf/launcher-custom.yml configuration file. Note that later options typically override earlier options (although this behavior is undefined and may be JVM-specific); this allows users to override the hard-coded options.

Packaging

To create a compressed, gzipped tar file, run the distTar task.

As part of package creation, this plugin will create three shell scripts:

• service/bin/[service-name]: a Gradle default start script for running the defined mainClass. This script is considered deprecated due to security issues with injectable Bash code; use the go-java-launcher binaries instead (see below).
• service/bin/<architecture>/go-java-launcher: native binaries for executing the specified mainClass, configurable via service/bin/launcher-static.yml and var/conf/launcher-custom.yml.
• service/bin/init.sh: a shell script to assist with daemonizing a JVM process. The script takes a single argument of start, stop, console or status.
  • start: On calls to service/bin/init.sh start, service/bin/<architecture>/go-java-launcher will be executed, disowned, and a pid file recorded in var/run/[service-name].pid.
  • console: like start, but does not background the process.
  • status: returns 0 when var/run/[service-name].pid exists and a process the id recorded in that file with a command matching the expected start command is found in the process table.
  • stop: if the process status is 0, issues a kill signal to the process.
• service/monitoring/bin/check.sh: a no-argument shell script that returns 0 when a service is healthy and non-zero otherwise. This script is generated if and only if checkArgs is specified above, and will run the singular command defined by invoking <mainClass> [checkArgs] to obtain health status.

In addition to creating these scripts, this plugin will merge the entire contents of ${projectDir}/service and ${projectDir}/var into the package.

The plugin also exposes the tar file as an artifact in the sls configuration, making it easy to share the artifact between sibling Gradle projects. For example:

configurations { tarballs }

dependencies {
    tarballs project(path: ':other-project', configuration: 'sls')
}

Running with Gradle

To run the main class using Gradle, run the run task.

Tasks

• distTar: creates the gzipped tar package
• createStartScripts: generates standard Java start scripts
• createInitScript: generates daemonizing init.sh script
• createManifest: generates a simple yaml file describing the package content
• run: runs the specified mainClass with default args

License

This plugin is made available under the Apache 2.0 License.