open-nomad/website/source/docs/drivers/exec.html.md

layout	page_title	sidebar_current	description
docs	Drivers: Exec	docs-drivers-exec	The Exec task driver is used to run binaries using OS isolation primitives.

Isolated Fork/Exec Driver

Name: exec

The exec driver is used to simply execute a particular command for a task. However, unlike raw_exec it uses the underlying isolation primitives of the operating system to limit the tasks access to resources. While simple, since the exec driver can invoke any command, it can be used to call scripts or other wrappers which provide higher level features.

Task Configuration

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

• command - The command to execute. Must be provided.

• artifact_source – (Optional) Source location of an executable artifact. Must be accessible from the Nomad client. If you specify an artifact_source to be executed, you must reference it in the command as show in the examples below

• 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) A list of arguments to the command.

Client Requirements

The exec driver can only be run when on Linux and running Nomad as root. exec is limited to this configuration because currently isolation of resources is only guaranteed on Linux. Further the host must have cgroups mounted properly in order for the driver to work.

You must specify a command to be executed. Optionally you can specify an artifact_source to be downloaded as well. Any command is assumed to be present on the running client, or a downloaded artifact.

Examples

To run a binary present on the Node:

  config {
    command = "/bin/sleep"
    args = 1
  }

To execute a binary specified by artifact_source:

  config {
    artifact_source = "https://dl.dropboxusercontent.com/u/1234/binary.bin"
    checksum = "sha256:abd123445ds4555555555"
    command = "$NOMAD_TASK_DIR/binary.bin"
  }

Client Attributes

The exec driver will set the following client attributes:

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

Resource Isolation

The resource isolation provided varies by the operating system of the client and the configuration.

On Linux, Nomad will use cgroups, and a chroot to isolate the resources of a process and as such the Nomad agent must be run as root.