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91 lines
3.0 KiB
Markdown
91 lines
3.0 KiB
Markdown
---
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layout: "docs"
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page_title: "Drivers: Java"
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sidebar_current: "docs-drivers-java"
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description: |-
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The Java task driver is used to run Jars using the JVM.
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---
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# Java Driver
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Name: `java`
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The `Java` driver is used to execute Java applications packaged into a Java Jar
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file. The driver requires the Jar file to be accessible from the Nomad
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client via the [`artifact` downloader](/docs/jobspec/index.html#artifact_doc).
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## Task Configuration
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The `java` driver supports the following configuration in the job spec:
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* `jar_path` - The path to the downloaded Jar. In most cases this will just be
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the name of the Jar. However, if the supplied artifact is an archive that
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contains the Jar in a subfolder, the path will need to be the relative path
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(`subdir/from_archive/my.jar`).
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* `args` - (Optional) A list of arguments to the optional `command`.
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References to environment variables or any [interpretable Nomad
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variables](/docs/jobspec/interpreted.html) will be interpreted
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before launching the task. For example:
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```
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args = ["${nomad.datacenter}", "${MY_ENV}", "${meta.foo}"]
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```
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* `jvm_options` - (Optional) A list of JVM options to be passed while invoking
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java. These options are passed without being validated in any way by Nomad.
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## Examples
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A simple config block to run a Java Jar:
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```
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task "web" {
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driver = "java"
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config {
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jar_path = "local/hello.jar"
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jvm_options = ["-Xmx2048m", "-Xms256m"]
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}
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# Specifying an artifact is required with the "java"
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# driver. This is the # mechanism to ship the Jar to be run.
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artifact {
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source = "https://dl.dropboxusercontent.com/u/1234/hello.jar"
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options {
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checksum = "md5:123445555555555"
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}
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}
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```
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## Client Requirements
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The `java` driver requires Java to be installed and in your system's `$PATH`. On
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Linux, Nomad must run as root since it will use `chroot` and `cgroups` which
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require root privileges. The task must also specify at least one artifact to
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download, as this is the only way to retrieve the Jar being run.
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## Client Attributes
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The `java` driver will set the following client attributes:
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* `driver.java` - Set to `1` if Java is found on the host node. Nomad determines
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this by executing `java -version` on the host and parsing the output
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* `driver.java.version` - Version of Java, ex: `1.6.0_65`
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* `driver.java.runtime` - Runtime version, ex: `Java(TM) SE Runtime Environment (build 1.6.0_65-b14-466.1-11M4716)`
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* `driver.java.vm` - Virtual Machine information, ex: `Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-466.1, mixed mode)`
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## Resource Isolation
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The resource isolation provided varies by the operating system of
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the client and the configuration.
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On Linux, Nomad will attempt to use cgroups, namespaces, and chroot
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to isolate the resources of a process. If the Nomad agent is not
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running as root, many of these mechanisms cannot be used.
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As a baseline, the Java jars will be run inside a Java Virtual Machine,
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providing a minimum amount of isolation.
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