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 currently requires the Jar file be accessible via HTTP from the Nomad client.

Task Configuration

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

• artifact_source - (Required) The hosted location of the source Jar file. Must be accessible from the Nomad client

• checksum - (Optional) The checksum type and value for the artifact_source image. The format is type:value, where type is any of md5, sha1, sha256, or sha512, and the value is the computed checksum. If a checksum is supplied and does not match the downloaded artifact, the driver will fail to start

• args - (Optional) The argument list for the java command, space separated.

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

Client Requirements

The java driver requires Java to be installed and in your systems $PATH. The artifact_source must be accessible by the node running Nomad. This can be an internal source, private to your cluster, but it must be reachable by the client over HTTP.

Examples

A simple config block to run a Java Jar:

# Define a task to run
task "web" {
  # Run a Java Jar
  driver = "java"

  config {
    artifact_source = "https://dl.dropboxusercontent.com/u/1234/hello.jar"
    checksum = "md5:123445555555555"
    jvm_options = "-Xmx2048m -Xms256m"
  }

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.