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This was not clear to me and is very important to understand since you can quickly fill up your disk if you run batch jobs.
135 lines
3.4 KiB
Markdown
135 lines
3.4 KiB
Markdown
---
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layout: "docs"
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page_title: "Drivers: Exec"
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sidebar_current: "docs-drivers-exec"
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description: |-
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The Exec task driver is used to run binaries using OS isolation primitives.
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---
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# Isolated Fork/Exec Driver
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Name: `exec`
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The `exec` driver is used to simply execute a particular command for a task.
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However, unlike [`raw_exec`](raw_exec.html) it uses the underlying isolation
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primitives of the operating system to limit the task's access to resources. While
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simple, since the `exec` driver can invoke any command, it can be used to call
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scripts or other wrappers which provide higher level features.
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## Task Configuration
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```hcl
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task "webservice" {
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driver = "exec"
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config {
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command = "my-binary"
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args = ["-flag", "1"]
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}
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}
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```
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The `exec` driver supports the following configuration in the job spec:
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* `command` - The command to execute. Must be provided. If executing a binary
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that exists on the host, the path must be absolute. If executing a binary that
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is downloaded from an [`artifact`](/docs/job-specification/artifact.html), the
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path can be relative from the allocations's root directory.
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* `args` - (Optional) A list of arguments to the `command`. References
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to environment variables or any [interpretable Nomad
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variables](/docs/runtime/interpolation.html) will be interpreted before
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launching the task.
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## Examples
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To run a binary present on the Node:
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```hcl
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task "example" {
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driver = "exec"
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config {
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# When running a binary that exists on the host, the path must be absolute.
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command = "/bin/sleep"
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args = ["1"]
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}
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}
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```
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To execute a binary downloaded from an
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[`artifact`](/docs/job-specification/artifact.html):
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```hcl
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task "example" {
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driver = "exec"
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config {
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command = "name-of-my-binary"
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}
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artifact {
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source = "https://internal.file.server/name-of-my-binary"
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options {
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checksum = "sha256:abd123445ds4555555555"
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}
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}
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}
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```
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## Client Requirements
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The `exec` driver can only be run when on Linux and running Nomad as root.
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`exec` is limited to this configuration because currently isolation of resources
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is only guaranteed on Linux. Further, the host must have cgroups mounted properly
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in order for the driver to work.
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If you are receiving the error:
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```
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* Constraint "missing drivers" filtered <> nodes
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```
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and using the exec driver, check to ensure that you are running Nomad as root.
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This also applies for running Nomad in -dev mode.
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## Client Attributes
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The `exec` driver will set the following client attributes:
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* `driver.exec` - This will be set to "1", indicating the driver is available.
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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 use cgroups, and a chroot to isolate the
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resources of a process and as such the Nomad agent must be run as root.
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### <a id="chroot"></a>Chroot
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The chroot is populated with data in the following directories from the host
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machine:
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```
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[
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"/bin",
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"/etc",
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"/lib",
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"/lib32",
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"/lib64",
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"/run/resolvconf",
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"/sbin",
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"/usr",
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]
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```
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Nomad will copy these directories into the job's chroot, so make sure you have
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enough disk space. Also take into consideration that allocations are not
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removed immediately after a job has completed, so you might need some margin if
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you run many batch jobs.
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This list is configurable through the agent client
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[configuration file](/docs/agent/configuration/client.html#chroot_env).
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