Micrometer in Spring Boot 3 – Detailed Interview Notes

✅ Introduction to Micrometer in Spring Boot 3

Micrometer is a metrics and observability library integrated into Spring Boot 3. It helps collect, expose, and export application signals such as:

• Metrics (numerical indicators)
• Tracing (request flows)
• Logs (event data)

It provides a vendor-neutral API, allowing integration with tools like Prometheus, Datadog, New Relic, Zipkin, and more.

---

🧱 Three Core Pillars of Observability

1. 📊 Metrics

• Quantitative data that describes system behavior
• Example: HTTP request count, response times, JVM memory usage

2. 📍 Tracing

• Tracks how requests move through various microservices
• Enables visualization of service dependencies and latencies

3. 📄 Logs

• Textual event records that capture errors, transactions, and internal events

---

🍽️ Metrics with Restaurant Analogy

Metric Type	Restaurant Analogy	Real-world Example
Counter	No. of customers entering	Total requests received by a service
Timer	Time to serve an order	HTTP request latency
Gauge	Number of pending orders	Jobs in queue or current memory usage

---

🧭 Understanding Tracing

🔹 What is Tracing?

Tracing is the process of tracking a request as it travels through one or more services.

🔑 Key Terms:

• Trace ID: Unique identifier for the entire request chain
• Span ID: Unique for each service/method call
• Parent Span ID: Shows nesting relationship between spans
• Context Propagation: Passing trace-related metadata (via headers like X-B3-TraceId) to preserve continuity across services

🔍 Example:

User calls /placeOrder → Service A calls Service B → Service B calls Service C. All services share a single Trace ID, each with a unique Span ID.

---

🚨 Importance of Micrometer Tracing

Without Tracing	With Micrometer Tracing
Difficult to correlate logs	Logs include trace & span identifiers
Bottlenecks are hard to detect	Easily identify slow service calls
Troubleshooting is slow	Can debug production using trace visuals

---

🆚 Spring Boot 2 vs Spring Boot 3

Feature	Spring Boot 2	Spring Boot 3
Tracing Integration	Not built-in	Integrated using Micrometer Tracing
Configuration	Required external libraries (Sleuth)	Auto-configured
Supported Bridges	N/A	Brave, OpenTelemetry
HTTP Monitoring	Manual	Automatic (for RestTemplate, WebClient)

---

🏗️ Micrometer Tracing Architecture

Client → Spring Boot App → Micrometer Bridge (Brave)
      → Exporter (Zipkin/Splunk) → Observability Platform

Components:

• Micrometer Tracing API: Abstract observability interfaces
• Bridge: Connects Micrometer to a tracing backend (e.g., Brave)
• Exporter/Reporter: Sends trace data to platforms (e.g., Zipkin)

---

📦 Required Dependencies (Maven)

<!-- Actuator for metrics -->
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

<!-- Micrometer tracing with Brave -->
<dependency>
  <groupId>io.micrometer</groupId>
  <artifactId>micrometer-tracing-bridge-brave</artifactId>
</dependency>

<!-- Zipkin exporter -->
<dependency>
  <groupId>io.zipkin.reporter2</groupId>
  <artifactId>zipkin-reporter-brave</artifactId>
</dependency>

---

⚙️ Practical Usage & Customization

✅ 1. Auto-track REST endpoints

Spring Boot automatically traces controller endpoints.

📝 2. Add Trace ID/Span ID to logs

logging:
  pattern:
    level: "%5p [${spring.application.name},%X{traceId},%X{spanId}]"

⏱️ 3. Create Custom Metrics using @Timed

@RestController
public class OrderController {

    @Timed(value = "order.process.time", description = "Time taken to process orders")
    @GetMapping("/order")
    public String processOrder() {
        return "Order processed";
    }
}

---

📈 Backend Integrations

Supported tools:

• Zipkin
• Jaeger
• Prometheus (for metrics)
• Grafana
• Elastic Stack
• Datadog, New Relic, Splunk

Configuration (YAML)

management:
  tracing:
    sampling:
      probability: 1.0
  zipkin:
    tracing:
      endpoint: http://localhost:9411/api/v2/spans

---

❓ Common Interview Questions

Conceptual:

• What are the differences between metrics, logs, and traces?
• How does context propagation work in Micrometer?
• What are Trace ID and Span ID? Why are they important?

Practical:

• How do you export traces to Zipkin in Spring Boot 3?
• How do you expose a custom metric using @Timed?
• What’s the role of Brave in Micrometer tracing?

---