gRPC for internal services in HLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is gRPC and why is it used for internal services?

gRPC is a fast, open-source remote procedure call (RPC) framework that uses HTTP/2 for transport. It is used for internal services because it supports efficient communication, strong typing with Protocol Buffers, and bi-directional streaming, making it ideal for microservices.

intermediate

How does gRPC use Protocol Buffers in service communication?

gRPC uses Protocol Buffers as its interface definition language and message format. This means service methods and message structures are defined in .proto files, which are then compiled to generate code for client and server, ensuring efficient and strongly typed communication.

intermediate

What are the benefits of HTTP/2 in gRPC for internal services?

HTTP/2 provides multiplexing (multiple requests over one connection), header compression, and server push. These features reduce latency and improve throughput, making gRPC communication between internal services faster and more efficient.

intermediate

Explain the difference between unary and streaming RPC in gRPC.

Unary RPC is a simple request-response where client sends one request and gets one response. Streaming RPC allows sending multiple messages: client streaming (client sends many, server responds once), server streaming (server sends many, client receives many), or bidirectional streaming (both send many).

advanced

What are common security practices when using gRPC for internal services?

Common practices include using TLS encryption for transport security, mutual TLS for authentication between services, and enforcing authorization policies. Since gRPC uses HTTP/2, it supports strong encryption and identity verification to protect internal communication.

What serialization format does gRPC primarily use?

A YAML

B JSON

C XML

D Protocol Buffers

gRPC uses Protocol Buffers as its default serialization format for efficient and strongly typed communication.

Which HTTP version does gRPC use for transport?

A HTTP/1.1

B HTTP/1.0

C HTTP/2

D HTTP/3

gRPC uses HTTP/2 to enable multiplexing, header compression, and low latency communication.

Which gRPC RPC type allows both client and server to send multiple messages?

A Bidirectional streaming RPC

B Client streaming RPC

C Unary RPC

D Server streaming RPC

Bidirectional streaming RPC allows both client and server to send multiple messages independently.

What is a key advantage of using gRPC for internal microservices?

A Uses slow text-based protocols

B Enables efficient, strongly typed communication

C Supports only REST APIs

D Does not support streaming

gRPC enables efficient, strongly typed communication using Protocol Buffers and HTTP/2.

Which security feature is commonly used with gRPC for internal service communication?

A Mutual TLS authentication

B Plain HTTP

C No encryption

D Basic authentication only

Mutual TLS is commonly used to authenticate and encrypt communication between internal gRPC services.

Describe how gRPC uses Protocol Buffers and HTTP/2 to improve internal service communication.

Think about how data is structured and sent between services.

Explain the different types of RPC calls supported by gRPC and when you might use each.

Consider the direction and number of messages exchanged.

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