Trace what happens between a user typing your URL and your container returning a response.
What they are really testing: A map of your mental model. They will use your answer to pick the next question, and the layers you skip reveal where your knowledge stops.
A real interview question
Trace what happens between a user typing your URL and your container returning a response.
What most people say
drag me
“DNS resolves the domain, the request hits the load balancer, and it forwards to the application.”
It is right and shallow. It leaves out TLS entirely, skips the ingress and service layers, and never mentions health checks, so it gives the interviewer nothing to probe and signals a thin model of the path.
The follow-ups they ask next
Where in that path would a 502 originate versus a 504?
502 is a proxy getting an invalid or absent response from upstream, so connectivity or immediate failure. 504 is a proxy timing out, so upstream was reachable but too slow. Both come from the proxy layer, not the app.
The user says the site is down but you see healthy traffic. Where do you look?
Between them and you: their DNS resolver caching an old record, their ISP or network, geographic routing, or a CDN edge failing in their region. Test resolution and connectivity from their location.
What the interviewer is listening for
- Includes TLS and ALPN
- Knows readiness gates service membership
- Frames the path as a bisection tool
What sinks the answer
- Skips TLS entirely
- No ingress or service layer
- Cannot use the path to localise a fault
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“[Browser and OS cache, then recursive DNS to authoritative]. Then [TCP handshake, then TLS with certificate validation and ALPN]. Then [CDN or edge, possibly served from cache], then [load balancer picking a health-checked backend], then [ingress matching rules, service selecting a ready pod], then [the app and its dependencies], and back out. Useful because [debugging becomes bisection by layer].”
Keep going with networking
Junior
What does a load balancer do during a deployment, and how does it know an instance is ready?
Senior
A service starts refusing connections under load, but CPU and memory are fine. What limits would you check?
Mid
Our pipeline takes 45 minutes and developers have stopped waiting for it. How do you fix that?
Mid
A pod is in CrashLoopBackOff after a deploy. Walk me through your debugging, command by command.
Mid
Terraform plan wants to destroy a production database that someone modified manually. What do you do?
Mid
You need to rename a heavily-used database column with zero downtime. How?
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