Use the Java task driver in a job

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.

Refer to Configure the Java task driver for capabilities, client requirements, and plugin configuration.

Task Configuration

task "webservice" {
  driver = "java"

  config {
    jar_path    = "local/example.jar"
    jvm_options = ["-Xmx2048m", "-Xms256m"]
  }
}

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

class - (Optional) The name of the class to run. If jar_path is specified and the manifest specifies a main class, this is optional. If shipping classes rather than a Jar, please specify the class to run and the class_path.
class_path - (Optional) The class_path specifies the class path used by Java to lookup classes and Jars.
jar_path - (Optional) 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 Jar's main method. References to environment variables or any interpretable Nomad variables will be interpreted before launching the task.
jvm_options - (Optional) A list of JVM options to be passed while invoking java. These options are passed without being validated in any way by Nomad.
pid_mode - (Optional) Set to "private" to enable PID namespace isolation for this task, or "host" to disable isolation. If left unset, the behavior is determined from the default_pid_mode in plugin configuration.

Warning: If set to "host", other processes running as the same user will be able to access sensitive process information like environment variables.

ipc_mode - (Optional) Set to "private" to enable IPC namespace isolation for this task, or "host" to disable isolation. If left unset, the behavior is determined from the default_ipc_mode in plugin configuration.

Warning: If set to "host", other processes running as the same user will be able to make use of IPC features, like sending unexpected POSIX signals.

cap_add - (Optional) A list of Linux capabilities to enable for the task. Effective capabilities (computed from cap_add and cap_drop) must be a subset of the allowed capabilities configured with allow_caps. Note that "all" is not permitted here if the allow_caps field in the driver configuration doesn't also allow all capabilities.

config {
  cap_add = ["net_raw", "sys_time"]
}

cap_drop - (Optional) A list of Linux capabilities to disable for the task. Effective capabilities (computed from cap_add and cap_drop) must be a subset of the allowed capabilities configured with allow_caps.

config {
  cap_drop = ["all"]
  cap_add  = ["chown", "sys_chroot", "mknod"]
}

work_dir - (Optional) Sets a custom working directory for the task. This path must be absolute and within the task's chroot or in a host volume mounted with a volume_mount block. This will also change the working directory when using nomad alloc exec.

Examples

A simple config block to run a Java Jar:

task "web" {
  driver = "java"

  config {
    jar_path    = "local/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://internal.file.server/hello.jar"

    options {
      checksum = "md5:123445555555555"
    }
  }
}

A simple config block to run a Java class:

task "web" {
  driver = "java"

  config {
    class       = "Hello"
    class_path  = "${NOMAD_TASK_DIR}"
    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://internal.file.server/Hello.class"

    options {
      checksum = "md5:123445555555555"
    }
  }
}