github.com/smintz/nomad@v0.8.3/website/source/docs/drivers/java.html.md (about) 1 --- 2 layout: "docs" 3 page_title: "Drivers: Java" 4 sidebar_current: "docs-drivers-java" 5 description: |- 6 The Java task driver is used to run Jars using the JVM. 7 --- 8 9 # Java Driver 10 11 Name: `java` 12 13 The `java` driver is used to execute Java applications packaged into a Java Jar 14 file. The driver requires the Jar file to be accessible from the Nomad 15 client via the [`artifact` downloader](/docs/job-specification/artifact.html). 16 17 ## Task Configuration 18 19 ```hcl 20 task "webservice" { 21 driver = "java" 22 23 config { 24 jar_path = "local/example.jar" 25 jvm_options = ["-Xmx2048m", "-Xms256m"] 26 } 27 } 28 ``` 29 30 The `java` driver supports the following configuration in the job spec: 31 32 * `class` - (Optional) The name of the class to run. If `jar_path` is specified 33 and the manifest specifies a main class, this is optional. If shipping classes 34 rather than a Jar, please specify the class to run and the `class_path`. 35 36 * `class_path` - (Optional) The `class_path` specifies the class path used by 37 Java to lookup classes and Jars. 38 39 * `jar_path` - (Optional) The path to the downloaded Jar. In most cases this will just be 40 the name of the Jar. However, if the supplied artifact is an archive that 41 contains the Jar in a subfolder, the path will need to be the relative path 42 (`subdir/from_archive/my.jar`). 43 44 * `args` - (Optional) A list of arguments to the Jar's main method. References 45 to environment variables or any [interpretable Nomad 46 variables](/docs/runtime/interpolation.html) will be interpreted before 47 launching the task. 48 49 * `jvm_options` - (Optional) A list of JVM options to be passed while invoking 50 java. These options are passed without being validated in any way by Nomad. 51 52 ## Examples 53 54 A simple config block to run a Java Jar: 55 56 ```hcl 57 task "web" { 58 driver = "java" 59 60 config { 61 jar_path = "local/hello.jar" 62 jvm_options = ["-Xmx2048m", "-Xms256m"] 63 } 64 65 # Specifying an artifact is required with the "java" driver. This is the 66 # mechanism to ship the Jar to be run. 67 artifact { 68 source = "https://internal.file.server/hello.jar" 69 70 options { 71 checksum = "md5:123445555555555" 72 } 73 } 74 } 75 ``` 76 77 A simple config block to run a Java class: 78 79 ```hcl 80 task "web" { 81 driver = "java" 82 83 config { 84 class = "Hello" 85 class_path = "${NOMAD_TASK_DIR}" 86 jvm_options = ["-Xmx2048m", "-Xms256m"] 87 } 88 89 # Specifying an artifact is required with the "java" driver. This is the 90 # mechanism to ship the Jar to be run. 91 artifact { 92 source = "https://internal.file.server/Hello.class" 93 94 options { 95 checksum = "md5:123445555555555" 96 } 97 } 98 } 99 ``` 100 101 ## Client Requirements 102 103 The `java` driver requires Java to be installed and in your system's `$PATH`. On 104 Linux, Nomad must run as root since it will use `chroot` and `cgroups` which 105 require root privileges. The task must also specify at least one artifact to 106 download, as this is the only way to retrieve the Jar being run. 107 108 ## Client Attributes 109 110 The `java` driver will set the following client attributes: 111 112 * `driver.java` - Set to `1` if Java is found on the host node. Nomad determines 113 this by executing `java -version` on the host and parsing the output 114 * `driver.java.version` - Version of Java, ex: `1.6.0_65` 115 * `driver.java.runtime` - Runtime version, ex: `Java(TM) SE Runtime Environment (build 1.6.0_65-b14-466.1-11M4716)` 116 * `driver.java.vm` - Virtual Machine information, ex: `Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-466.1, mixed mode)` 117 118 Here is an example of using these properties in a job file: 119 120 ```hcl 121 job "docs" { 122 # Only run this job where the JVM is higher than version 1.6.0. 123 constraint { 124 attribute = "${driver.java.version}" 125 operator = ">" 126 value = "1.6.0" 127 } 128 } 129 ``` 130 131 ## Resource Isolation 132 133 The resource isolation provided varies by the operating system of 134 the client and the configuration. 135 136 On Linux, Nomad will attempt to use cgroups, namespaces, and chroot 137 to isolate the resources of a process. If the Nomad agent is not 138 running as root, many of these mechanisms cannot be used. 139 140 As a baseline, the Java jars will be run inside a Java Virtual Machine, 141 providing a minimum amount of isolation.