SLS Distribution Gradle Plugins

A set of Gradle plugins that facilitate packaging projects for distributions conforming to Palantir's Service Layout Specification. This project was formerly known as gradle-java-distribution.

The Java Service and Asset plugins cannot both be applied to the same gradle project, and distributions from both are produced as a gzipped tar named [service-name]-[project-version].sls.tgz.

Java Service Distribution Gradle Plugin

Similar to the standard application plugin, this plugin helps package Java Gradle projects for easy distribution and execution. This distribution conforms with Palantir's SLS service layout 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.

Asset Distribution Gradle Plugin

This plugin helps package static files and directories into a distribution that conforms with Palantir's SLS asset layout conventions. Asset distributions differ from service distributions in that they do not have a top-level service or var directory, and instead utilize a top-level asset directory that can contain arbitrary files.

Usage

Java Service Distribution plugin

Apply the plugin using standard Gradle convention:

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

A sample configuration for the Service plugin:

distribution {
    serviceName 'my-service'
    serviceGroup 'my.service.group'
    mainClass 'com.palantir.foo.bar.MyServiceMainClass'
    args 'server', 'var/conf/my-service.yml'
    env 'KEY1': 'value1', 'KEY2': 'value1'
    manifestExtensions 'KEY3': 'value2'
    productDependency {
        productGroup = "other-group"
        productName = "other-service"
        minimumVersion = "1.1.0"
        maximumVersion = "1.5.x"
        recommendedVersion = "1.3.0"
    }
}

And the complete list of configurable properties:

• (optional) serviceName the name of this service, used to construct the final artifact's file name. Defaults to the configured "name" of the Gradle project, project.name.
• (optional) serviceGroup the group of the service, used in the final artifact's manifest. Defaults to the configured "group" of the Gradle project, project.group.
• (optional) manifestExtensions a map of extended manifest attributes, as specified in SLS 1.0
• (optional) productDependency adds an entry to the extensions.product-dependencies block of the SLS manifest, declaring that this service has a dependency on the given other service with specific version bounds. The productDependency object must specify the following properties:
  • productGroup the serviceGroup of the dependency.
  • productName the serviceName of the dependency.
  • minVersion the minimal compatible version of the dependency.
  • maxVersion the maximal compatible version of the dependency.
  • recommended the version developers think you should use; most commonly the version of the implementation that was tested during CI (minVersion typically matches the version of the api you use to negotiate).
• 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) env a map of environment variables that will be placed into the env block of the static launcher config. See go-java-launcher for details on the custom environment block.
• (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 ${projectDir}/var) to exclude from the distribution, defaulting to ['log', 'run'].
• (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.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.

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.

Runtime environment variables

Environment variables can be configured through the env blocks of launcher-static.yml and launcher-custom.yml as described in configuration file. They are set by the launcher process before the Java process is executed.

Directories created at runtime

The plugin configures go-java-launcher to create the following directories before starting the service:

• var/data/tmp

Additionally, the following directories are created in every SLS distribution created:

• var/log
• var/run

Asset Distribution plugin

Apply the plugin using standard Gradle convention:

plugins {
    id 'com.palantir.sls-asset-distribution'
}

A sample configuration for the Asset plugin:

distribution {
    serviceName 'my-assets'
    assets 'relative/path/to/assets', 'relocated/path/in/dist'
    assets 'another/path, 'another/relocated/path'
}

The complete list of configurable properties:

• serviceName the name of this service, used to construct the final artifact's file name.
• (optional) serviceGroup the group of the service, used in the final artifact's manifest. Defaults to the configured "group" of the Gradle project, project.group.
• (optional) manifestExtensions a map of extended manifest attributes, as specified in SLS 1.0.
• (optional) serviceDependency adds an entry to the extensions.service-dependencies block of the SLS manifest, declaring that this service has a dependency on the given other service with specific version bounds.
• (optional) assets <fromPath> adds the specified file or directory (recursively) to the asset distribution, preserving the directory structure. For example, assets 'foo/bar' yields files foo/bar/baz/1.txt and foo/bar/2.txt in the asset distribution, assuming that the directory foo/bar contains files baz/1.txt and 2.txt.
• (optional) assets <fromPath> <toPath> as above, but adds the specified files relative to toPath in the asset distribution. For example, assets 'foo/bar' 'baz' yields files baz/baz/1.txt and baz/2.txt assuming that the directory foo/bar contains the files baz/1.txt and 2.txt.
• (optional) setAssets <map<fromPath, toPath>> as above, but removes all prior configured assets.

The example above, when applied to a project rooted at ~/project, would create a distribution with the following structure:

[service-name]-[service-version]/
    deployment/
        manifest.yml                      # simple package manifest
    asset/
        relocated/path/in/dist            # contents from `~/project/relative/path/to/assets/`
        another/relocated/path            # contents from `~/project/another/path`

Note that repeated calls to assets are processed in-order, and as such, it is possible to overwrite resources by specifying that a later invocation be relocated to a previously used destination's ancestor directory.

Packaging

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

The plugins expose 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')
}

As part of package creation, the Java Service plugin will additionally 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.

Furthermore, the Java Service plugin will merge the entire contents of ${projectDir}/service and ${projectDir}/var into the package.

Tasks

• distTar: creates the gzipped tar package
• createManifest: generates a simple yaml file describing the package content

Specific to the Java Service plugin:

• createStartScripts: generates standard Java start scripts
• createInitScript: generates daemonizing init.sh script
• run: runs the specified mainClass with default args

License

This plugin is made available under the Apache 2.0 License.