hashicorp/nomad · error

Task can only ask for 'cpu' or 'cores' resource, not both.

Error message

Task can only ask for 'cpu' or 'cores' resource, not both.

What it means

Appended by Resources.Validate when a task resource block sets both CPU (MHz) and Cores. Nomad permits either the legacy cpu-based accounting or the newer cores-based one, never both on the same task.

Source

Thrown at nomad/structs/structs.go:2424

	}
}

// DiskInBytes returns the amount of disk resources in bytes.
func (r *Resources) DiskInBytes() int64 {
	return int64(r.DiskMB * BytesInMegabyte)
}

const (
	// MemoryNoLimit is a sentinel value indicating there is no upper hard
	// memory limit
	MemoryNoLimit = -1
)

func (r *Resources) Validate() error {
	var mErr multierror.Error

	if r.Cores > 0 && r.CPU > 0 {
		mErr.Errors = append(mErr.Errors, errors.New("Task can only ask for 'cpu' or 'cores' resource, not both."))
	}

	if r.Cores < 0 {
		mErr.Errors = append(mErr.Errors, fmt.Errorf("cores value (%d) cannot be negative", r.Cores))
	}

	if err := r.MeetsMinResources(); err != nil {
		mErr.Errors = append(mErr.Errors, err)
	}

	// Ensure the task isn't asking for disk resources
	if r.DiskMB > 0 {
		mErr.Errors = append(mErr.Errors, errors.New("Task can't ask for disk resources, they have to be specified at the task group level."))
	}

	// Ensure devices are valid
	devices := set.New[string](len(r.Devices))
	for i, d := range r.Devices {

View on GitHub (pinned to 482b49bf1a)

Solutions

  1. Remove the cpu field and keep cores (recommended for whole-core granularity)
  2. Or remove cores and keep cpu (MHz) for finer-grained sizing

Example fix

// before
resources {
  cpu    = 2000
  cores  = 2
  memory = 1024
}
// after
resources {
  cores  = 2
  memory = 1024
}
Defensive patterns

Strategy: validation

Validate before calling

function validateCpuExclusive(resources) {
  if ((resources.cores ?? 0) > 0 && (resources.cpu ?? 0) > 0) {
    throw new Error("task resources: set either cpu (MHz) or cores, not both");
  }
}

Type guard

function hasValidCpuSpec(r) { return !((r.cores ?? 0) > 0 && (r.cpu ?? 0) > 0); }

Try / catch

try {
  await nomad.jobs.validate(job);
} catch (e) {
  if (e.message.includes("'cpu' or 'cores' resource, not both")) {
    console.error("Pick one CPU sizing field per task");
  } else throw e;
}

Prevention

When it happens

Trigger: A task resources block (or Resources struct) with cores > 0 and cpu > 0 simultaneously during job validation.

Common situations: Jobs written after Nomad 1.1 introduced cores, where a base template set cpu and the operator added cores; tooling merging resource defaults with overrides.

Related errors

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/2450f55f35f25e5e. Report an issue: GitHub.