kataras/iris · error

failed to connect to the server after %d retries

Error message

failed to connect to the server after %d retries

What it means

The Waiter polls the server address with exponential backoff after startup; if none of the retries can establish a connection it returns this error, meaning the server did not become reachable in time.

Source

Thrown at core/host/waiter.go:119

			// Increase the retry interval by the base raised to the power of the number of attempts.
			/*
				0	2 seconds
				1	4 seconds
				2	8 seconds
				3	~16 seconds
				4	~32 seconds
				5	~64 seconds
				6	~128 seconds
				7	~256 seconds
				8	~512 seconds
				...
			*/
			retryInterval = time.Duration(math.Pow(base, float64(i+1))) * time.Second
		}
	}
	// All attempts failed, return an error.
	return fmt.Errorf("failed to connect to the server after %d retries", maxRetries)
}

// Fail is called by the server's Run method when the server failed to start.
func (w *Waiter) Fail(err error) {
	w.mu.Lock()
	w.failure = err
	w.mu.Unlock()
}

func (w *Waiter) getFailure() error {
	w.mu.RLock()
	err := w.failure
	w.mu.RUnlock()
	return err
}

View on GitHub (pinned to 7bedaf55a0)

Solutions

1. Inspect the server's failure via Waiter.Fail logs / Run error to find the root cause (e.g. "port already in use").
2. Free the port or choose another one; ensure the process can bind the address.
3. Increase maxRetries/startup timeout in slow environments, or check that the app actually called ListenAndServe.
4. Verify networking (firewall, docker port mapping, IPv4/IPv6 mismatch) allows connecting to the address.

Example fix

// before
w.Wait(addr) // fails after N retries
// after
if err := w.Wait(addr); err != nil {
    log.Fatalf("server not reachable: %v; root cause: %v", err, w.(*host.Waiter).GetFailure())
}

// pre-check port availability before starting the server
conn, err := net.DialTimeout("tcp", addr, time.Second)
if err == nil { conn.Close(); return errors.New("port already in use") }

if err := w.Wait(addr); err != nil {
    if failure := waiter.GetFailure(); failure != nil {
        log.Fatalf("server start failed: %v (root cause: %v)", err, failure)
    }
    // optionally retry startup with backoff
}

When it happens

Trigger: Calling host Wait / supervisor Wait when the HTTP server failed to bind (port in use, permission denied) or crashed before accepting connections; firewall blocking localhost connect.

Common situations: Port already occupied; trying to bind a privileged port (<1024) without permissions; server panicked at startup; running in a container where the address resolves differently.

Understand the failure class

Background: ECONNREFUSED and "connection refused" / "could not connect to server" errors: what they mean and how to fix them — this error's family across 44 libraries.

Related errors

• failed to connect to the server after %d retries
• err
• auth: configuration: %w
• multipart related: next part: read: %w
• port already in use: %w

AI-assisted analysis of kataras/iris@7bedaf55a0 (2026-08-30). Data as JSON: /api/errors/b42241f50c94d533. Report an issue: GitHub.