FastAPI Backend Interview Guide
The bank tests explanation, diagnosis, and tradeoff judgment. It is not a list of definitions to memorize.
How to practice
For each question:
- Give a 30 to 60 second answer.
- Name one production failure or tradeoff.
- Describe how you would test or observe the behavior.
- Answer the follow-up without changing your original assumptions silently.
If a question is underspecified, state the requirement that changes the design. Senior interviews often evaluate whether you identify missing constraints before selecting technology.
Banks
- Beginner: Python web basics, HTTP, schemas, routes, dependencies, and CRUD.
- Intermediate: sessions, async, authentication, middleware, testing, Docker, Redis, and jobs.
- Advanced: transactions, concurrency, performance, delivery guarantees, security, and observability.
- Senior: boundaries, failure economics, multi-tenancy, high traffic, migrations, and technical decisions.
- Scenario-based: realistic incidents and design exercises with investigation paths.
- Topic drills: short prompts grouped by Python, HTTP, data, security, testing, architecture, and operations.
A useful answer shape
Short answer
Answer the actual question in a few sentences. Name the primary decision.
Deeper explanation
Explain the mechanism or guarantee. Distinguish concepts that are often conflated.
Practical example
Describe a request, query, failure, or small implementation. Examples demonstrate that the definition has operational meaning.
Senior-level discussion
State tradeoffs, failure cases, scaling behavior, security boundaries, or what evidence would change the choice.
Common follow-ups
Prepare for the next layer rather than ending with a slogan.
Evaluation rubric
| Signal | Weak | Strong |
|---|---|---|
| Correctness | Repeats framework marketing | Names the actual protocol or runtime behavior |
| Scope | Assumes one universal context | States traffic, consistency, latency, and ownership assumptions |
| Failure awareness | Describes success path only | Covers timeout, duplicate, concurrency, and partial failure |
| Security | Adds auth as a final bullet | Defines identity, resource policy, tenant scope, and data exposure |
| Operability | Says "monitor it" | Names signals, thresholds, and an investigation path |
| Tradeoffs | Selects tools by popularity | Explains cost, alternatives, and revisit conditions |
Whiteboard habit
For system-design questions, draw the synchronous path first. Mark every network boundary, state owner, transaction, and queue. Then add cache, replicas, and asynchronous processing only where a requirement demands them.