What is the difference between monitoring and observability, and what are the main signals you would collect for a web service?
What the interviewer wants to hear
- Monitoring checks known failure modes with dashboards and alerts
- Observability lets you ask new questions about unknown problems
- Metrics, logs and traces as core signals
- Golden signals: latency, traffic, errors, saturation
- Correlation through shared IDs and labels
Model answer
Monitoring is watching for problems you already know about: you define dashboards and alerts for things like error rate or disk space. Observability is a property of the system: how well you can understand its internal state from the data it emits, including problems you never predicted. In practice you need both. For a web service I would collect metrics for the four golden signals: latency, traffic, errors and saturation, mostly with Prometheus. I would ship structured logs with request IDs to a central store, and add distributed traces with OpenTelemetry so I can follow one request across services. The key is correlation: the same service, version and trace ID labels on all three signals, so I can jump from an alert on a metric to example traces and then to the logs for exactly those requests.
Can you answer it under time pressure?
Take a timed easy round and get scored on every answer.
More easy DevOps Engineer questions
- What does DevOps mean to you, and how is it different from a traditional operations team?
- Walk me through the stages of a typical CI/CD pipeline you would build for a web service.
- How is a container different from a virtual machine? When would you choose one over the other?
- What is Infrastructure as Code and why is it better than creating resources by clicking in the cloud console?
- Explain how a Deployment, a Service and an Ingress work together to expose a web app in Kubernetes.
- Compare trunk-based development with GitFlow. Which would you choose for a team that deploys several times a day, and why?
- Walk me through what happens when you run docker run -p 8080:80 nginx:1.27 on a fresh machine.
- How does a load balancer use health checks, and what makes a good health check endpoint?
- Terraform and Ansible are both called infrastructure as code. How do they differ, and when would you use each?