Port Binding Failures

Symptom

The deployment fails with error code PORT_MISMATCH or CONTAINER_CRASH_LOOP. The logs show the server started but the deployment timed out after 5 minutes.

What it means

Kubeletto could not reach your container. A Knative endpoint requires listening on all host interfaces (0.0.0.0) on the port allocated in the system configuration.

Most likely causes

• Hardcoding the port inside your application code (e.g. app.listen(3000)) instead of checking $PORT.
• Binding to the local interface 127.0.0.1 or localhost, making the container unreachable from the external host network.

How to diagnose it

Check your application logs. Ensure you see standard startup lines showing binding actions:

kubeletto logs my-service --tail 100

How to fix it

Modify your startup code to read the environment variable PORT and bind to 0.0.0.0. Example in Node.js:

const port = process.env.PORT || 8080;
app.listen(port, "0.0.0.0", () => {
  console.log(`Server running on port ${port}`);
});