open-nomad/website/source/docs/drivers/java.html.md

layout	page_title	sidebar_current	description
docs	Drivers: Java	docs-drivers-java	The Java task driver is used to run Jars using the JVM.

Java Driver

Name: java

The Java driver is used to execute Java applications packaged into a Java Jar file. The driver requires the Jar file to be accessible from the Nomad client via the artifact downloader.

Task Configuration

The java driver supports the following configuration in the job spec:

• jar_path - The path to the downloaded Jar. In most cases this will just be the name of the Jar. However, if the supplied artifact is an archive that contains the Jar in a subfolder, the path will need to be the relative path (subdir/from_archive/my.jar).

• args - (Optional) A list of arguments to the optional command. References to environment variables or any intepretable Nomad variables will be interpreted before launching the task. For example:

      args = ["${nomad.datacenter}", "${MY_ENV}", "${meta.foo}"]
  

• jvm_options - (Optional) A list of JVM options to be passed while invoking java. These options are passed not validated in any way in Nomad.

Examples

A simple config block to run a Java Jar:

task "web" {
  driver = "java"

  config {
    jar_path = "hello.jar"
    jvm_options = "-Xmx2048m -Xms256m"
  }

  # Specifying an artifact is required with the "java"
  # driver. This is the # mechanism to ship the Jar to be run.
  artifact {
    source = "https://dl.dropboxusercontent.com/u/1234/hello.jar"

    options {
      checksum = "md5:123445555555555"
    }
  }

Client Requirements

The java driver requires Java to be installed and in your systems $PATH. The task must also specify at least one artifact to download as this is the only way to retrieve the Jar being run.

Client Attributes

The java driver will set the following client attributes:

• driver.java - Set to 1 if Java is found on the host node. Nomad determines this by executing java -version on the host and parsing the output
• driver.java.version - Version of Java, ex: 1.6.0_65
• driver.java.runtime - Runtime version, ex: Java(TM) SE Runtime Environment (build 1.6.0_65-b14-466.1-11M4716)
• driver.java.vm - Virtual Machine information, ex: Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-466.1, mixed mode)

Resource Isolation

The resource isolation provided varies by the operating system of the client and the configuration.

On Linux, Nomad will attempt to use cgroups, namespaces, and chroot to isolate the resources of a process. If the Nomad agent is not running as root many of these mechanisms cannot be used.

As a baseline, the Java jars will be run inside a Java Virtual Machine, providing a minimum amount of isolation.