What causes "expected duration found %T for %s" in cloudflare/cloudflared?

Write the value as a duration string with a unit in the config file (grace-period: 30s).

expected duration found %T for %s

Error message

expected duration found %T for %s

What it means

Type-mismatch error in configFileSettings.Duration: a config-file setting read as a duration is neither a time.Duration nor a duration string (e.g. it is an int, bool, or map in the parsed YAML). The accessor returns zero and this error instead of guessing a conversion.

Source

Thrown at config/configuration.go:297

func (c *configFileSettings) Int(name string) (int, error) {
	if raw, ok := c.Settings[name]; ok {
		if v, ok := raw.(int); ok {
			return v, nil
		}
		return 0, fmt.Errorf("expected int found %T for %s", raw, name)
	}
	return 0, nil
}

func (c *configFileSettings) Duration(name string) (time.Duration, error) {
	if raw, ok := c.Settings[name]; ok {
		switch v := raw.(type) {
		case time.Duration:
			return v, nil
		case string:
			return time.ParseDuration(v)
		}
		return 0, fmt.Errorf("expected duration found %T for %s", raw, name)
	}
	return 0, nil
}

func (c *configFileSettings) Float64(name string) (float64, error) {
	if raw, ok := c.Settings[name]; ok {
		if v, ok := raw.(float64); ok {
			return v, nil
		}
		return 0, fmt.Errorf("expected float found %T for %s", raw, name)
	}
	return 0, nil
}

func (c *configFileSettings) String(name string) (string, error) {
	if raw, ok := c.Settings[name]; ok {
		if v, ok := raw.(string); ok {
			return v, nil

View on GitHub (pinned to 2253eeeb25)

Solutions

Write the value as a duration string with a unit in the config file (grace-period: 30s).
If a bare number is intentional seconds, change the call site to read Int and multiply by time.Second.
Handle the ParseDuration error path separately for string values with bad formats.

Example fix

// before (config.yml)
grace-period: 30
// after
grace-period: 30s

Defensive patterns

Strategy: validation

Validate before calling

// Go
typeAssertDuration := func(v interface{}) (time.Duration, error) {
    switch t := v.(type) {
    case time.Duration: return t, nil
    case string: return time.ParseDuration(t)
    default: return 0, fmt.Errorf("not a duration: %T", v)
    }
}

Type guard

func asDuration(v interface{}) (time.Duration, bool) { d, ok := v.(time.Duration); return d, ok }

Try / catch

d, err := settings.Duration("grace-period")
if err != nil {
    log.Printf("'grace-period' must be like 30s/5m: %v", err)
    return err
}

Prevention

Always include a unit suffix for durations in config files
Validate duration strings with time.ParseDuration in CI
Document expected units next to each duration setting

When it happens

Trigger: Calling Duration(name) where the stored value is an int, bool, or a string in an invalid format is handled separately (ParseDuration error); this error fires for non-duration, non-string types — e.g. `grace-period: 5` (bare number instead of "5s").

Common situations: Users writing bare numbers in YAML where a duration string like 30s/1m is required; config keys copied from examples with wrong units.

Understand the failure class

Background: "invalid duration" / "failed to parse duration": why your timeout, interval, or TTL string is rejected and which formats each library accepts — this error's family across 32 libraries.

Related errors

AI-assisted analysis of cloudflare/cloudflared@2253eeeb25 (2026-09-06). Data as JSON: /api/errors/eb947521f92d3250. Report an issue: GitHub.