gRPC for internal services in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why choose gRPC over REST for internal services?

Consider a company deciding between gRPC and REST for communication between its internal microservices. Which of the following is the main advantage of using gRPC in this context?

A gRPC uses HTTP/2 which supports multiplexing and reduces latency compared to REST over HTTP/1.1

B gRPC only supports synchronous calls, which simplifies service design

C gRPC requires no schema definition, so services can evolve independently without coordination

D gRPC messages are always human-readable JSON, making debugging easier than REST

💡 Hint

Think about protocol efficiency and network features.

gRPC uses HTTP/2 which allows multiplexing multiple calls over a single connection, reducing latency and improving performance compared to REST which typically uses HTTP/1.1.

❓ Architecture

intermediate

Designing service communication with gRPC

You are designing an internal system with multiple microservices. Which architectural pattern best fits gRPC usage for service-to-service communication?

A Use gRPC to expose public APIs directly to external clients

B Use gRPC for synchronous request-response calls between services with defined protobuf contracts

C Use gRPC as a replacement for database queries within services

D Use gRPC only for asynchronous event streaming and avoid request-response patterns

💡 Hint

Consider typical gRPC usage patterns inside microservice architectures.

gRPC is ideal for synchronous request-response communication between internal services using protobuf contracts to define messages and services.

❓ scaling

advanced

Scaling gRPC services under high load

Your internal gRPC service is experiencing high traffic and latency spikes. Which approach best helps scale the service efficiently?

A Switch to REST APIs to reduce overhead from HTTP/2 multiplexing

B Increase the size of protobuf messages to reduce the number of calls

C Implement client-side load balancing with multiple service instances and use connection pooling

D Disable streaming features to simplify the protocol

💡 Hint

Think about how gRPC clients can distribute load and reuse connections.

Client-side load balancing with multiple instances and connection pooling helps distribute requests and reduce latency under high load.

❓ tradeoff

advanced

Tradeoffs of using gRPC streaming internally

What is a key tradeoff when using gRPC streaming for internal service communication?

A Streaming reduces latency but increases complexity in error handling and resource management

B Streaming always improves throughput without any drawbacks

C Streaming eliminates the need for service discovery

D Streaming requires all clients to be implemented in the same programming language

💡 Hint

Consider the operational challenges of long-lived connections.

While streaming can reduce latency and improve throughput, it adds complexity in managing connection lifecycle, errors, and resource usage.

❓ estimation

expert

Estimating capacity for gRPC internal services

You expect 10,000 requests per second to your internal gRPC service. Each request takes 5ms to process on average. How many service instances do you need to handle the load without queuing, assuming each instance can handle requests sequentially?

A At least 200 instances

B At least 500 instances

C At least 1000 instances

D At least 50 instances

💡 Hint

Calculate how many requests one instance can handle per second, then divide total requests by that.

One instance handles 1 / 0.005 = 200 requests per second. For 10,000 requests, 10,000 / 200 = 50 instances are needed to handle the load without queuing.

Practice

1. What is the main advantage of using gRPC for communication between internal services?

easy

A. It provides fast and efficient communication using HTTP/2 and Protocol Buffers.

B. It uses plain text JSON for easy debugging.

C. It requires no schema definition for messages.

D. It only works for external client-server communication.

Solution

1. Step 1: Understand gRPC communication basics

   gRPC uses HTTP/2 for transport and Protocol Buffers for message serialization, making it fast and efficient.

2. Step 2: Compare options with gRPC features

   Options A and B are incorrect because gRPC uses binary Protocol Buffers, not JSON, and requires schema definitions. It only works for external client-server communication. is wrong because gRPC is often used internally.

3. Final Answer:

   It provides fast and efficient communication using HTTP/2 and Protocol Buffers. -> Option A

4. Quick Check:

   gRPC speed and efficiency = It provides fast and efficient communication using HTTP/2 and Protocol Buffers. [OK]

Hint: Remember gRPC uses HTTP/2 + Protocol Buffers for speed [OK]

Common Mistakes:

• Confusing gRPC with REST using JSON
• Thinking gRPC doesn't need schemas
• Assuming gRPC is only for external APIs

2. Which of the following is the correct way to define a gRPC service method in a Protocol Buffers (.proto) file?

easy

A. service UserService { function GetUser (UserRequest) returns UserResponse; }

B. service UserService { call GetUser (UserRequest) returns UserResponse; }

C. service UserService { method GetUser (UserRequest) -> UserResponse; }

D. service UserService { rpc GetUser (UserRequest) returns (UserResponse); }

Solution

1. Step 1: Recall gRPC service syntax in .proto files

   The correct syntax uses rpc MethodName(RequestType) returns (ResponseType); inside a service block.

2. Step 2: Match options to correct syntax

   Only service UserService { rpc GetUser (UserRequest) returns (UserResponse); } matches the exact gRPC syntax. Others use incorrect keywords like function, method, or call.

3. Final Answer:

   service UserService { rpc GetUser (UserRequest) returns (UserResponse); } -> Option D

4. Quick Check:

   gRPC method syntax = service UserService { rpc GetUser (UserRequest) returns (UserResponse); } [OK]

Hint: Look for 'rpc' keyword inside service block [OK]

Common Mistakes:

• Using 'function' or 'method' instead of 'rpc'
• Omitting parentheses around request/response types
• Misplacing 'returns' keyword

3. Given this gRPC service definition snippet:

service OrderService {
  rpc CreateOrder (OrderRequest) returns (OrderResponse);
}

What happens when a client calls CreateOrder with invalid data that violates the schema?

medium

A. The server returns a validation error before processing the request.

B. The server accepts the request and processes it anyway.

C. The client call fails at compile time due to schema mismatch.

D. The server crashes due to invalid input.

Solution

1. Step 1: Understand gRPC schema validation

   gRPC uses Protocol Buffers which enforce message structure. Invalid data is rejected by the server with an error.

2. Step 2: Evaluate options based on gRPC behavior

   The server returns a validation error before processing the request. is correct because the server validates input and returns errors. The server accepts the request and processes it anyway. is unsafe and incorrect. The client call fails at compile time due to schema mismatch. is wrong because client code compiles but runtime validation happens. The server crashes due to invalid input. is incorrect as servers handle errors gracefully.

3. Final Answer:

   The server returns a validation error before processing the request. -> Option A

4. Quick Check:

   gRPC input validation = The server returns a validation error before processing the request. [OK]

Hint: Invalid data triggers server validation error, not crash [OK]

Common Mistakes:

• Assuming client compile-time failure for invalid data
• Thinking server processes invalid requests
• Believing server crashes on bad input

4. You notice that your internal gRPC service calls are slow and sometimes timeout. Which of the following is the best first step to debug this issue?

medium

A. Remove Protocol Buffers and switch to JSON messages.

B. Rewrite all services to use REST instead of gRPC.

C. Check network latency and HTTP/2 connection health between services.

D. Increase client timeout without investigating.

Solution

1. Step 1: Identify common causes of gRPC slowness

   Network issues and HTTP/2 connection problems often cause delays in gRPC calls.

2. Step 2: Evaluate debugging approaches

   Check network latency and HTTP/2 connection health between services. is the best first step to diagnose root cause. Options B and C are drastic changes without diagnosis. Increase client timeout without investigating. ignores the problem source.

3. Final Answer:

   Check network latency and HTTP/2 connection health between services. -> Option C

4. Quick Check:

   Debug gRPC slowness = Check network latency and HTTP/2 connection health between services. [OK]

Hint: Start debugging network and HTTP/2 before changing code [OK]

Common Mistakes:

• Jumping to rewrite services without diagnosis
• Ignoring network as a cause
• Blindly increasing timeouts

5. You are designing an internal microservices system using gRPC. Which design choice best improves scalability and fault isolation?

hard

A. Avoid using Protocol Buffers and send raw JSON over gRPC.

B. Define small, focused gRPC services with clear method boundaries and use load balancing.

C. Use gRPC only for external APIs and REST internally.

D. Combine all functionality into one large gRPC service to reduce network calls.

Solution

1. Step 1: Understand microservices design principles with gRPC

   Small, focused services with clear APIs improve scalability and fault isolation. Load balancing helps distribute load.

2. Step 2: Evaluate design options

   Define small, focused gRPC services with clear method boundaries and use load balancing. aligns with best practices. Combine all functionality into one large gRPC service to reduce network calls. creates a monolith, hurting scalability. Use gRPC only for external APIs and REST internally. wastes gRPC benefits internally. Avoid using Protocol Buffers and send raw JSON over gRPC. breaks gRPC efficiency by avoiding Protocol Buffers.

3. Final Answer:

   Define small, focused gRPC services with clear method boundaries and use load balancing. -> Option B

4. Quick Check:

   Microservices + gRPC best practice = Define small, focused gRPC services with clear method boundaries and use load balancing. [OK]

Hint: Small services + load balancing = scalable gRPC design [OK]

Common Mistakes:

• Building large monolithic gRPC services
• Using REST internally instead of gRPC
• Ignoring Protocol Buffers benefits