ServiceNow Site Reliability Engineer Interview: Rounds, Questions and Preparation

What the job involves

Site Reliability Engineers (SREs) keep large-scale production systems reliable, fast, and available. They blend software engineering with systems and operations work: building automation, monitoring, incident response, and capacity planning. At global tech companies, SREs work on distributed cloud services and often share on-call duties.

Role and Technical Knowledge

1. 1

   What does an SRE do differently from a traditional sysadmin or DevOps engineer?

   Highlight the software engineering approach to operations, SLOs, error budgets, automation, and reducing toil. Mention that SREs code to solve reliability problems.

2. 2

   Explain SLI, SLO, and SLA with an example for a web service.

   Define each term clearly: SLI is a measured metric (e.g., latency), SLO is a target (e.g., 99.9% under 200ms), SLA is a contract with consequences. Give a concrete service example.

3. 3

   How would you monitor a microservice-based application? What tools and metrics would you use?

   Cover the four golden signals (latency, traffic, errors, saturation), distributed tracing, logging, and tools like Prometheus, Grafana, Jaeger, or ELK. Mention alerting on SLO breaches.

4. 4

   What is an error budget and how does it influence release decisions?

   Explain that error budget is 1 minus SLO. If budget is exhausted, freeze feature releases and focus on reliability. Show how it balances innovation and stability.

Practical Scenarios

1. 5

   A production service is returning 500 errors for 10% of requests. Walk me through your troubleshooting steps.

   Start with dashboards and logs, check recent deployments, isolate by region or instance, verify dependencies, and use rollback or mitigation. Communicate status and document findings.

2. 6

   How would you automate the deployment of a service to reduce manual errors?

   Describe a CI/CD pipeline with automated tests, canary or blue-green deployment, infrastructure as code, and rollback triggers. Mention tools like Jenkins, GitLab CI, or ArgoCD.

3. 7

   You need to reduce alert noise. What steps would you take?

   Focus on actionable alerts, tune thresholds, use multi-condition alerts, group related alerts, and route to the right team. Emphasize SLO-based alerting over raw metric alerts.

4. 8

   A database is running out of disk space in production. What do you do?

   Check growth rate and largest tables, archive or purge old data, add storage if possible, and set up proactive disk usage alerts. Mention safe cleanup and backup before changes.

Coding and Systems Fundamentals

1. 9

   Write a Python script to parse a log file and count the number of ERROR lines per hour.

   Use file reading, datetime parsing, and a dictionary to aggregate counts. Show clean code, error handling, and mention scalability for large files.

2. 10

   Explain how DNS resolution works when you type a URL in a browser.

   Cover recursive resolver, root, TLD, and authoritative servers, caching, and the difference between A, CNAME, and MX records. Keep it concise and structured.

3. 11

   What happens when you run a command like 'kubectl get pods' in a Kubernetes cluster?

   Describe kubectl sending a request to the API server, authentication, authorization, and the API server fetching state from etcd. Mention that it does not directly talk to nodes.

4. 12

   How would you design a simple health check endpoint for a service?

   Include checks for dependencies (database, cache), return appropriate HTTP status codes, and avoid heavy operations. Mention liveness vs readiness probes in Kubernetes.

Behavioural and HR Questions

1. 13

   Tell me about a time you fixed a technical problem under pressure. What was the outcome?

   Use STAR format: situation, task, action, result. Highlight calm troubleshooting, communication, and a measurable improvement or lesson learned.

2. 14

   How do you handle being on call and getting paged at 3 AM?

   Show willingness to share on-call, follow runbooks, escalate when needed, and focus on restoring service first. Mention blameless postmortems and improving systems to reduce pages.

3. 15

   Describe a situation where you had to learn a new technology quickly for a project.

   Give a specific example, the approach you took (docs, tutorials, small experiments), and how you applied it successfully. Show curiosity and self-learning.

4. 16

   Why do you want to work as a Site Reliability Engineer at a global tech company?

   Connect your interest in large-scale systems, automation, and reliability with the company's scale and culture. Avoid generic answers; mention specific SRE practices you admire.