Service-to-service communication in Spring Boot - Performance & Optimization

Performance: Service-to-service communication

MEDIUM IMPACT

This affects the speed and responsiveness of backend interactions that impact frontend load times and user experience.

Calling another microservice synchronously for data

Spring Boot

private final WebClient webClient = WebClient.create();
Mono<String> response = webClient.get().uri("http://service/api/data").retrieve().bodyToMono(String.class);

Uses non-blocking WebClient with connection pooling, freeing threads and improving scalability.

📈 Performance GainNon-blocking calls improve throughput and reduce latency under load

Calling another microservice synchronously for data

Spring Boot

RestTemplate restTemplate = new RestTemplate();
String response = restTemplate.getForObject("http://service/api/data", String.class);

Creates a new RestTemplate instance per call and blocks thread until response arrives, causing thread starvation under load.

📉 Performance CostBlocks thread, increasing response time and reducing throughput

Performance Comparison

Pattern	Thread Usage	Latency Impact	Network Cost	Verdict
Synchronous RestTemplate per call	Blocks thread	High latency	Medium	[X] Bad
Non-blocking WebClient with pooling	Non-blocking	Low latency	Medium	[OK] Good
Sequential service calls	Blocks threads sequentially	High cumulative latency	Medium	[X] Bad
Parallel reactive calls	Non-blocking	Low cumulative latency	Medium	[OK] Good
Large payloads	N/A	High latency	High	[X] Bad
Minimal DTOs with compression	N/A	Low latency	Low	[OK] Good

Rendering Pipeline

Service-to-service communication affects backend response times that influence frontend rendering speed and interaction readiness.

→Network

→Backend Processing

→Frontend Rendering

⚠️ BottleneckNetwork latency and blocking backend threads

Core Web Vital Affected

INP

This affects the speed and responsiveness of backend interactions that impact frontend load times and user experience.

Optimization Tips

1Use non-blocking HTTP clients like WebClient instead of blocking RestTemplate.

2Parallelize multiple service calls to reduce total wait time.

3Send only necessary data in payloads and use compression to reduce network cost.

Performance Quiz - 3 Questions

Which pattern improves backend responsiveness for service-to-service calls?

A Making synchronous calls sequentially

B Using non-blocking WebClient with connection pooling

C Creating a new RestTemplate instance per call

D Sending full large JSON payloads every time

DevTools: Network and Performance panels

How to check: Use Network panel to inspect request sizes and timings; use Performance panel to record backend response times and frontend interaction delays.

What to look for: Look for long backend response times, large payload sizes, and blocking main thread during interactions.

Practice

1. What is the main purpose of service-to-service communication in Spring Boot microservices?

easy

A. To create user interfaces for microservices

B. To allow different microservices to exchange data and work together

C. To store data in a database

D. To compile Java code faster

Solution

1. Step 1: Understand microservices architecture

   Microservices are small services that work independently but often need to share data or trigger actions in other services.

2. Step 2: Identify the role of service-to-service communication

   This communication allows microservices to interact and cooperate by exchanging data or requests.

3. Final Answer:

   To allow different microservices to exchange data and work together -> Option B

4. Quick Check:

   Service communication = microservices working together [OK]

Hint: Microservices talk to each other to share data [OK]

Common Mistakes:

• Confusing service communication with UI creation
• Thinking it manages database storage
• Assuming it speeds up code compilation

2. Which of the following is the correct way to create a RestTemplate bean in Spring Boot for service-to-service calls?

easy

A. @Component
public void restTemplate() {
return new RestTemplate();
}

B. @Service
public RestTemplate restTemplate() {
return new RestTemplate();
}

C. @Bean
public RestTemplate restTemplate() {
return new RestTemplate();
}

D. RestTemplate restTemplate = new RestTemplate();

Solution

1. Step 1: Understand Spring bean creation

   To create a reusable RestTemplate, define a method annotated with @Bean inside a @Configuration class.

2. Step 2: Check the correct syntax

   @Bean public RestTemplate restTemplate() { return new RestTemplate(); } correctly uses @Bean and returns a new RestTemplate instance.

3. Final Answer:

   @Bean public RestTemplate restTemplate() { return new RestTemplate(); } -> Option C

4. Quick Check:

   @Bean method returns RestTemplate instance [OK]

Hint: Use @Bean to create reusable RestTemplate [OK]

Common Mistakes:

• Using @Service instead of @Bean
• Not returning RestTemplate instance
• Missing @Bean annotation

3. Given the following Spring Boot code snippet using WebClient, what will be the output if the called service returns "Hello from Service B"?

WebClient client = WebClient.create("http://service-b/api/greet");
String response = client.get()
    .retrieve()
    .bodyToMono(String.class)
    .block();
System.out.println(response);

medium

A. "Hello from Service B"

B. null

C. An exception is thrown

D. "Error: Service not found"

Solution

1. Step 1: Understand WebClient call

   The WebClient sends a GET request to the URL and retrieves the response body as a String.

2. Step 2: Analyze the response handling

   The block() method waits for the response synchronously and returns the body content.

3. Final Answer:

   "Hello from Service B" -> Option A

4. Quick Check:

   WebClient returns response body string [OK]

Hint: block() waits and returns response body string [OK]

Common Mistakes:

• Assuming asynchronous call returns immediately
• Expecting null without response
• Confusing error message with normal output

4. Identify the error in this Spring Boot service-to-service call using RestTemplate:

@Autowired
private RestTemplate restTemplate;

public String callService() {
    String url = "http://service-c/api/data";
    ResponseEntity<String> response = restTemplate.getForEntity(url, String.class);
    return response.getBody();
}

medium

A. getForEntity method does not exist

B. URL string is missing protocol

C. ResponseEntity cannot hold String type

D. RestTemplate bean is not defined in the configuration

Solution

1. Step 1: Check RestTemplate injection

   The RestTemplate must be defined as a bean for @Autowired to inject it properly.

2. Step 2: Verify URL and method usage

   The URL includes protocol and getForEntity is a valid method returning ResponseEntity<String>.

3. Final Answer:

   RestTemplate bean is not defined in the configuration -> Option D

4. Quick Check:

   Missing RestTemplate bean causes injection error [OK]

Hint: Always define RestTemplate as a @Bean before autowiring [OK]

Common Mistakes:

• Forgetting to create RestTemplate bean
• Using incomplete URL
• Misunderstanding getForEntity method

5. You want to call Service D from Service E using WebClient with a timeout of 2 seconds and handle errors gracefully. Which code snippet correctly implements this?

hard

A. WebClient client = WebClient.create("http://service-d/api");
String result = client.get()
.retrieve()
.bodyToMono(String.class)
.timeout(Duration.ofSeconds(2))
.onErrorReturn("Timeout or error")
.block();

B. WebClient client = WebClient.create();
String result = client.get()
.uri("http://service-d/api")
.retrieve()
.bodyToMono(String.class)
.block(Duration.ofSeconds(2));

C. RestTemplate restTemplate = new RestTemplate();
restTemplate.setTimeout(2000);
String result = restTemplate.getForObject("http://service-d/api", String.class);

D. WebClient client = WebClient.builder()
.baseUrl("http://service-d/api")
.build();
String result = client.get()
.retrieve()
.bodyToMono(String.class)
.block();

Solution

1. Step 1: Setup WebClient with timeout and error handling

   WebClient client = WebClient.create("http://service-d/api"); String result = client.get() .retrieve() .bodyToMono(String.class) .timeout(Duration.ofSeconds(2)) .onErrorReturn("Timeout or error") .block(); uses timeout(Duration.ofSeconds(2)) to limit wait time and onErrorReturn to provide fallback on errors.

2. Step 2: Verify other options

   WebClient client = WebClient.create(); String result = client.get() .uri("http://service-d/api") .retrieve() .bodyToMono(String.class) .block(Duration.ofSeconds(2)); but uses block(Duration) which times out and throws an exception instead of providing a fallback; RestTemplate restTemplate = new RestTemplate(); restTemplate.setTimeout(2000); String result = restTemplate.getForObject("http://service-d/api", String.class); tries to set timeout on RestTemplate incorrectly; WebClient client = WebClient.builder() .baseUrl("http://service-d/api") .build(); String result = client.get() .retrieve() .bodyToMono(String.class) .block(); lacks timeout and error handling.

3. Final Answer:

   WebClient client = WebClient.create("http://service-d/api"); String result = client.get() .retrieve() .bodyToMono(String.class) .timeout(Duration.ofSeconds(2)) .onErrorReturn("Timeout or error") .block(); -> Option A

4. Quick Check:

   Timeout + onErrorReturn = safe WebClient call [OK]

Hint: Use timeout() and onErrorReturn() for safe WebClient calls [OK]

Common Mistakes:

• Using block(Duration) which is invalid
• Trying to set timeout directly on RestTemplate
• Ignoring error handling in WebClient calls