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I apologize in advance for the rather long PR, but unfortunately there is not an easy way to break this up into smaller chunks. This separates the agent configuration into smaller, more consumable pieces just like the job specification.
130 lines
3.1 KiB
Markdown
130 lines
3.1 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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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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