Task API

Nomad's Task API provides every task managed by Nomad with a Unix Domain Socket (UDS) to access the local agent's HTTP API. Regardless of agent configuration the Task API does not require mTLS, but always requires authentication. See below for details.

The Unix Domain Socket is located at ${NOMAD_SECRETS_DIR}/api.sock.

Rationale

Nomad's HTTP API is available on every agent at the configured bind_addr. While this is convenient for user access, it is not always accessible to workloads running on Nomad. These workloads may have a network configuration that makes it impossible to access the agent HTTP address, or the agent's HTTP address may be difficult for workloads to discover in a way that's portable between Nomad nodes and clusters.

A Unix Domain Socket is a way to expose network services that works with most runtimes and operating systems and adds minimal complexity or runtime overhead to Nomad.

Security

Unlike the agent's HTTP API, the Task API always requires authentication even if ACLs are disabled. This allows Nomad to always make the Task API available even if the workload is untrusted. If ACLs are enabled, the anonymous policy is not available via the Task API.

Both ACL Tokens and Workload Identities are accepted. Once the Task API has authenticated the credentials, the normal endpoint-specific authorization is applied when ACLs are enabled.

The Workload Identity should be used by tasks accessing the Task API.

An ACL Token should be used when an operator is accessing the Task API via nomad alloc exec or when a task is proxying Nomad HTTP requests on behalf of an authenticated user. The Task API could be used by a proxy presenting Nomad's UI with a standard TLS certificate for browsers.

If task.user is set in the jobspec, the Task API will only be usable by that user. Otherwise the Unix Domain Socket is accessible by any user.

mTLS is never enabled for the Task API since traffic never leaves the node.

Using the Task API

The following jobspec will use the Task API to set [Dynamic Node Metadata][dnm] and exit.

job "taskapi-example" {
  type = "batch"

  group "taskapi-example" {

    task "taskapi" {
      driver = "docker"

      config {
        image = "curlimages/curl:7.87.0"
        args = [
          "--unix-socket", "${NOMAD_SECRETS_DIR}/api.sock",
          "-H", "Authorization: Bearer ${NOMAD_TOKEN}",
          "--data-binary", "{\"Meta\": {\"example\": \"Hello World!\"}}",
          "--fail-with-body",
          "--verbose",
          "localhost/v1/client/metadata",
        ]
      }

      identity {
        env = true
      }
    }
  }
}

If the job was able to run successfully after about 10 seconds you can observe the outcome by searching for the updated Node's metadata:

$ nomad node status -filter 'Meta.example == "Hello World!"'