Raw Fork/Exec Driver

Name: raw_exec

The raw_exec driver is used to execute a command for a task without any isolation. Further, the task is started as the same user as the Nomad process. As such, it should be used with extreme care and is disabled by default.

Task Configuration

task "webservice" {
  driver = "raw_exec"

  config {
    command = "my-binary"
    args    = ["-flag", "1"]
  }
}

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

• command - The command to execute. Must be provided. If executing a binary that exists on the host, the path must be absolute. If executing a binary that is downloaded from an artifact, the path can be relative from the allocation's root directory.

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

Examples

To run a binary present on the Node:

task "example" {
  driver = "raw_exec"

  config {
    # When running a binary that exists on the host, the path must be absolute/
    command = "/bin/sleep"
    args    = ["1"]
  }
}

To execute a binary downloaded from an artifact:

task "example" {
  driver = "raw_exec"

  config {
    command = "name-of-my-binary"
  }

  artifact {
    source = "https://internal.file.server/name-of-my-binary"
    options {
      checksum = "sha256:abd123445ds4555555555"
    }
  }
}

Client Requirements

The raw_exec driver can run on all supported operating systems. For security reasons, it is disabled by default. To enable raw exec, the Nomad client configuration must explicitly enable the raw_exec driver in the plugin's options:

plugin "raw_exec" {
  config {
    enabled = true
  }
}

Nomad versions before v0.9 use the following client configuration. This configuration is also supported in Nomad v0.9.0, but is deprecated in favor of the plugin stanza:

client {
  options = {
    "driver.raw_exec.enable" = "1"
  }
}

Plugin Options

• enabled - Specifies whether the driver should be enabled or disabled. Defaults to false.

• no_cgroups - Specifies whether the driver should not use cgroups to manage the process group launched by the driver. By default, cgroups are used to manage the process tree to ensure full cleanup of all processes started by the task. The driver uses cgroups by default on Linux and when /sys/fs/cgroup/freezer/nomad is writable for the Nomad process. Using a cgroup significantly reduces Nomad's CPU usage when collecting process metrics.

Client Options

• driver.raw_exec.enable - Specifies whether the driver should be enabled or disabled. Defaults to false.

• driver.raw_exec.no_cgroups - Specifies whether the driver should not use cgroups to manage the process group launched by the driver. By default, cgroups are used to manage the process tree to ensure full cleanup of all processes started by the task. The driver only uses cgroups when Nomad is launched as root, on Linux and when cgroups are detected.

Client Attributes

The raw_exec driver will set the following client attributes:

• driver.raw_exec - This will be set to "1", indicating the driver is available.

Resource Isolation

The raw_exec driver provides no isolation.

If the launched process creates a new process group, it is possible that Nomad will leak processes on shutdown unless the application forwards signals properly. Nomad will not leak any processes if cgroups are being used to manage the process tree. Cgroups are used on Linux when Nomad is being run with appropriate privileges, the cgroup system is mounted and the operator hasn't disabled cgroups for the driver.