What causes "MaxRunDuration must be greater than zero" in hashicorp/nomad?

Change the hostname to a valid DNS name (letters, digits, hyphens, dot-separated labels).

MaxRunDuration must be greater than zero

Error message

MaxRunDuration must be greater than zero

What it means

When a network stanza declares a hostname, Nomad validates it as a DNS name (unless it contains a ${...} interpolation). A hostname that fails dns.IsDomainName, e.g. containing underscores, spaces, or invalid characters, triggers this error.

Source

Thrown at nomad/structs/structs.go:7150

	if tg.Count < 0 {
		mErr = multierror.Append(mErr, errors.New("Task group count can't be negative"))
	}

	if len(tg.Tasks) == 0 {
		// could be a lone consul gateway inserted by the connect mutator
		mErr = multierror.Append(mErr, errors.New("Missing tasks for task group"))
	}

	if tg.Disconnect != nil {
		if err := tg.Disconnect.Validate(j); err != nil {
			mErr = multierror.Append(mErr, err)
		}
	}

	if tg.MaxRunDuration != nil {
		if *tg.MaxRunDuration <= 0 {
			mErr = multierror.Append(mErr, errors.New("MaxRunDuration must be greater than zero"))
		}

		switch j.Type {
		case JobTypeBatch, JobTypeSysBatch:
		default:
			mErr = multierror.Append(mErr, fmt.Errorf("Job type %q does not allow max_run_duration", j.Type))
		}
	}

	for idx, constr := range tg.Constraints {
		if err := constr.Validate(); err != nil {
			outer := fmt.Errorf("Constraint %d validation failed: %s", idx+1, err)
			mErr = multierror.Append(mErr, outer)
		}
	}
	if j.Type == JobTypeSystem {
		if tg.Affinities != nil {
			mErr = multierror.Append(mErr, fmt.Errorf("System jobs may not have an affinity block"))

View on GitHub (pinned to 482b49bf1a)

Solutions

Change the hostname to a valid DNS name (letters, digits, hyphens, dot-separated labels).
Use an interpolation like hostname = "${attr.unique.network.ip-address}" if dynamic naming is needed.
Validate the name with a DNS regex before submitting the job.

Example fix

// before
network {
  hostname = "my_host"
}
// after
network {
  hostname = "my-host"
}

Defensive patterns

Strategy: validation

Validate before calling

if net.Hostname != "" && !strings.Contains(net.Hostname, "${") {
    if _, ok := dns.IsDomainName(net.Hostname); !ok {
        return fmt.Errorf("hostname %q is not a valid DNS name", net.Hostname)
    }
}

Type guard

func validDNSName(s string) bool {
    var re = regexp.MustCompile(`^(?i)[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?(\.[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?)*$`)
    return re.MatchString(s)
}

Prevention

Use only letters, digits, and hyphens in hostnames
Prefer interpolation (${...}) for dynamic values
Validate hostnames in CI before deploying job specs

When it happens

Trigger: Submitting a job whose group network block sets hostname to something like "my_host" or "web server"; any non-interpolated value that is not a valid domain name.

Common situations: Using underscores in hostnames (common mistake); names with spaces or trailing dots from templating; forgetting that interpolated values are skipped but literal ones are validated.

Related errors

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/f03f6d6f2b40d929. Report an issue: GitHub.