hashicorp/nomad · error

Task %s validation failed: %v

Error message

Task %s validation failed: %v

What it means

Produced during job validation when `task.Validate(j.Type, tg)` fails for a task inside a task group. Nomad wraps the task's own validation error as 'Task %s validation failed: %v' and appends it to the group multierror. It means one task's config (driver, resources, artifacts, services, templates, etc.) is invalid for the job's type.

Source

Thrown at nomad/structs/structs.go:7319

		mErr = multierror.Append(mErr, outer)
	}

	// Validate group service script-checks
	if err := tg.validateScriptChecksInGroupServices(); err != nil {
		outer := fmt.Errorf("Task group service check validation failed: %v", err)
		mErr = multierror.Append(mErr, outer)
	}

	// Validate the scaling policy
	if err := tg.validateScalingPolicy(j); err != nil {
		outer := fmt.Errorf("Task group scaling policy validation failed: %v", err)
		mErr = multierror.Append(mErr, outer)
	}

	// Validate the tasks
	for _, task := range tg.Tasks {
		if err := task.Validate(j.Type, tg); err != nil {
			outer := fmt.Errorf("Task %s validation failed: %v", task.Name, err)
			mErr = multierror.Append(mErr, outer)
		}
	}

	return mErr.ErrorOrNil()
}

func (tg *TaskGroup) validateNetworks() error {
	var mErr multierror.Error
	portLabels := make(map[string]string)
	// host_network -> static port tracking
	staticPortsIndex := make(map[string]map[int]string)
	cniArgKeys := set.New[string](len(tg.Networks))

	for _, net := range tg.Networks {
		for _, port := range append(net.ReservedPorts, net.DynamicPorts...) {
			if other, ok := portLabels[port.Label]; ok {
				mErr.Errors = append(mErr.Errors, fmt.Errorf("Port label %s already in use by %s", port.Label, other))

View on GitHub (pinned to 482b49bf1a)

Solutions

1. Read the wrapped '%v' detail to see which task stanza failed
2. Run `nomad job validate <file>` locally to catch the exact task error before submit
3. Fix the offending field in the named task (driver, resources, services, template, artifact...)
4. Ensure referenced port labels and group-level stanzas exist in the parent task group
5. Compare against a known-good example for the driver/version you target

Example fix

// before
task "app" {
  driver = "dockr"
  resources {
    cpu    = -100
    memory = 0
  }
}
// after
task "app" {
  driver = "docker"
  resources {
    cpu    = 500
    memory = 256
  }
}

func validateTasks(j *api.Job) error {
  var errs error
  for _, tg := range j.TaskGroups {
    for _, t := range tg.Tasks {
      if t.Driver == "" { errs = multierror.Append(errs, fmt.Errorf("task %s: missing driver", t.Name)) }
      if r := t.Resources; r != nil {
        if r.CPU < 0 || r.MemoryMB < 0 { errs = multierror.Append(errs, fmt.Errorf("task %s: negative resources", t.Name)) }
      }
      // port label refs in services must exist in group network
      labels := map[string]bool{}
      for _, n := range tg.Networks { for _, p := range n.ReservedPorts { labels[p.Label] = true }; for _, p := range n.DynamicPorts { labels[p.Label] = true } }
      for _, s := range t.Services { if s.PortLabel != "" && !labels[s.PortLabel] { errs = multierror.Append(errs, fmt.Errorf("task %s: unknown port label %q", t.Name, s.PortLabel)) } }
    }
  }
  return errs
}

func taskValid(t *api.Task) bool {
  return t.Name != "" && t.Driver != "" && t.Resources != nil &&
    t.Resources.CPU >= 0 && t.Resources.MemoryMB >= 0
}

When it happens

Trigger: Registering a job where a task has: an unknown/unavailable driver name, invalid resource stanza (negative CPU/memory, memory above limits), invalid service/check definitions, bad artifact sources, invalid template stanza, invalid log config, or a task field not permitted for the given job type.

Common situations: Typo in driver name (e.g. "docker" misspelled); referencing task group network port labels that don't exist; memory oversubscription fields on older Nomad versions; copy-pasted task stanzas carrying fields from another driver; template/consul misconfigurations caught at submit time.

Related errors

• Task group %s validation failed: %v
• Job type %q does not allow update block
• Job type %q does not allow migrate block
• Task group scaling policy validation failed: %v
• Template %d validation failed: %s

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/4b02800e00cdc15d. Report an issue: GitHub.