Easy interview questions in Backend Dev, page 4
How do you include a router in your main FastAPI app?
Create APIRouter in another file, import it into main.py, then call app.include_router(router).
What is the difference between defining a Rust trait and implementing it?
Define with trait and signatures; implement with impl Trait for Type and concrete bodies.
How do you choose between relational and NoSQL databases?
Relational gives schema, joins, and ACID for structured related data; document gives flexible schema and horizontal scale for varied or denormalized data.
Design an Express route to create a user
POST to a collection URL like /users, read the payload from req.body via express.json(), return 201 with the created resource.
What is the CAP theorem?
Consistency, Availability, Partition tolerance; during a network partition you must choose between staying consistent or staying available.
req.params vs req.query vs req.body in Express
Req.params holds named route segments, req.query holds the URL query string, req.body holds the parsed payload.
Status codes for successful POST and GET
201 Created for a successful POST (ideally with a Location header), 200 OK for a successful GET returning data.
What is the fundamental difference between a goroutine and an OS thread?
This tests your grasp of Go's M:N scheduler. A strong answer notes that goroutines are runtime-managed, multiplexed onto OS threads, and use far less memory per unit, enabling thousands of concurrent tasks.
What is the difference between async def and regular functions?
This tests async def call semantics. A strong answer contrasts regular functions, which execute immediately, with async def, which returns a coroutine object that does nothing until awaited or wrapped in create_task.
How do Send and Sync prevent data races? Give a Send-but-not-Sync example.
Explain Send moves values and Sync allows shared references across threads; give Cell as Send but not Sync because it has interior mutability.
Explain await's purpose, awaitable types, and event loop signaling
This tests whether you understand await as a yield point. A strong answer lists three awaitables (coroutines, Tasks, Futures), explains await yields control to the event loop until completion, and warns that a bare coroutine call does not run it.
Buffered vs unbuffered Go channels and deadlock scenario
Tests channel synchronization semantics. Unbuffered channels block until sender and receiver rendezvous; buffered channels block only when full or empty. Deadlock: goroutine sends on unbuffered channel with no receiver.
What is the difference between OLTP and OLAP?
OLTP handles many short read-write transactions on normalized current data; OLAP runs few large analytical scans over denormalized historical data.
What is a star schema?
A central fact table of measures and foreign keys surrounded by denormalized dimension tables of descriptive attributes, joined in one hop for fast, simple analytical queries.
Define a Mongoose schema and model
New mongoose.Schema with field options (type, required, default), then mongoose.model('Product', schema) to get a model.
What is the difference between ETL and ELT?
ETL transforms before loading, on a separate engine; ELT loads raw then transforms inside a scalable warehouse. Choose ELT with cloud warehouses and large raw or schema-on-read data.
How do you initialize and manage Go dependencies?
Init with go mod init; use go get and go mod tidy; go.mod sets path and versions, go.sum stores checksums for verified builds.
What is the difference between Cargo.toml and Cargo.lock?
Cargo.toml declares broad requirements; Cargo.lock pins exact resolved versions.
Describe SQLAlchemy setup in FastAPI from database config to endpoint
Tests FastAPI dependency injection and SQLAlchemy session lifecycle. Good answers cover: engine with pooling, declarative models, a yield-based session dependency, and endpoint queries. Red flag: engine per request or global session shared everywhere.
What is database replication and why use it?
Replication keeps copies of data on multiple servers; primary benefits are high availability through failover and improved read scalability by spreading reads.
We are hiring for this. Every open role lists the topics its interview covers, so you can prepare for the real thing rather than guessing.
See open roles