openfaas/faas · error

invalid value for max_idle_conns_per_host: %s

Error message

invalid value for max_idle_conns_per_host: %s

What it means

Thrown by ReadConfig in gateway/types/readconfig.go at startup when the max_idle_conns_per_host environment variable is set but is not a plain base-10 integer (strconv.Atoi fails). ReadConfig returns the error and the gateway process fails to boot. Leaving the variable unset is safe: the default of 1024 applies.

Source

Thrown at gateway/types/readconfig.go:159

	cfg.MaxIdleConns = 1024
	cfg.MaxIdleConnsPerHost = 1024

	maxIdleConns := hasEnv.Getenv("max_idle_conns")
	if len(maxIdleConns) > 0 {
		val, err := strconv.Atoi(maxIdleConns)
		if err != nil {
			return nil, fmt.Errorf("invalid value for max_idle_conns: %s", maxIdleConns)
		}
		cfg.MaxIdleConns = val

	}

	maxIdleConnsPerHost := hasEnv.Getenv("max_idle_conns_per_host")
	if len(maxIdleConnsPerHost) > 0 {
		val, err := strconv.Atoi(maxIdleConnsPerHost)
		if err != nil {
			return nil, fmt.Errorf("invalid value for max_idle_conns_per_host: %s", maxIdleConnsPerHost)
		}
		cfg.MaxIdleConnsPerHost = val

	}

	cfg.AuthProxyURL = hasEnv.Getenv("auth_proxy_url")
	cfg.AuthProxyPassBody = parseBoolValue(hasEnv.Getenv("auth_proxy_pass_body"))

	cfg.Namespace = hasEnv.Getenv("function_namespace")

	return &cfg, nil
}

// GatewayConfig provides config for the API Gateway server process
type GatewayConfig struct {

	// HTTP timeout for reading a request from clients.
	ReadTimeout time.Duration

View on GitHub (pinned to 8d803bf9e2)

Solutions

1. Set max_idle_conns_per_host to a bare decimal integer, e.g. max_idle_conns_per_host=256
2. Remove the variable to fall back to the default of 1024
3. Check the manifest/ConfigMap for whitespace, commas or unit suffixes in the value
4. Validate both *_conns variables against ^[0-9]+$ in CI

Example fix

# before
  max_idle_conns_per_host: "256Mi"

# after
  max_idle_conns_per_host: "256"

# validate before deploying the gateway
if [ -n "$max_idle_conns_per_host" ] && ! [[ "$max_idle_conns_per_host" =~ ^[0-9]+$ ]]; then
  echo "max_idle_conns_per_host must be an integer, got: $max_idle_conns_per_host" >&2
  exit 1
fi

func isBase10Int(s string) bool {
	_, err := strconv.Atoi(s)
	return err == nil
}

When it happens

Trigger: Setting max_idle_conns_per_host to a non-integer value such as "256 " with trailing whitespace, "1,024", "0.5", "1e2" or "per-host" via kubectl, Helm values, docker-compose environment or a ConfigMap entry with a stray newline.

Common situations: Copying a documented example with a comma separator; ConfigMap block scalars adding trailing newlines; CI templating injecting whitespace; confusing the variable with a memory-size style value like "256Mi".

Related errors

• invalid value for max_idle_conns: %s
• A body is required for this endpoint
• err.Error()
• Unable to parse list of functions from provider

AI-assisted analysis of openfaas/faas@8d803bf9e2 (2026-08-16). Data as JSON: /api/errors/f09618e54fad1b4b. Report an issue: GitHub.