Metrics with Micrometer in Spring Boot

Introduction

Micrometer helps you measure how your Spring Boot app is doing. It tracks things like how fast requests are or how many errors happen.

You want to see how many users visit your website each minute.

You need to check if your app is slow or fast during certain times.

You want to count how many times a feature is used.

You want to watch for errors or failures in your app.

You want to send app performance data to monitoring tools like Prometheus.

Syntax

Spring Boot

import io.micrometer.core.instrument.MeterRegistry;
import org.springframework.stereotype.Component;

@Component
public class MyMetrics {
    private final MeterRegistry meterRegistry;

    public MyMetrics(MeterRegistry meterRegistry) {
        this.meterRegistry = meterRegistry;
    }

    public void recordEvent() {
        meterRegistry.counter("myapp.events.count").increment();
    }
}

MeterRegistry is the main object to create and update metrics.

Use counters to count events, timers to measure durations, and gauges for current values.

Examples

This counts how many requests happened.

Spring Boot

meterRegistry.counter("requests.total").increment();

This measures how long a block of code takes.

Spring Boot

import io.micrometer.core.instrument.Timer;

Timer.Sample sample = Timer.start(meterRegistry);
// code to time
sample.stop(meterRegistry.timer("requests.latency"));

This tracks the current size of a queue.

Spring Boot

meterRegistry.gauge("queue.size", queue, Queue::size);

Sample Program

This Spring Boot app has one endpoint /hello. Each time you visit it, Micrometer counts the request.

Spring Boot

package com.example.metricsdemo;

import io.micrometer.core.instrument.MeterRegistry;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
public class MetricsDemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(MetricsDemoApplication.class, args);
    }
}

@RestController
class DemoController {
    private final MeterRegistry meterRegistry;

    public DemoController(MeterRegistry meterRegistry) {
        this.meterRegistry = meterRegistry;
    }

    @GetMapping("/hello")
    public String hello() {
        meterRegistry.counter("hello.requests.count").increment();
        return "Hello, Micrometer!";
    }
}

Important Notes

Micrometer works with many monitoring systems like Prometheus, Datadog, and others.

Spring Boot auto-configures Micrometer if you add the right starter dependency.

Remember to name your metrics clearly so they are easy to understand later.

Summary

Micrometer helps track app performance and events easily.

Use counters, timers, and gauges for different types of metrics.

Spring Boot makes it simple to add Micrometer and start measuring.

Practice

1. What is the primary purpose of Micrometer in a Spring Boot application?

easy

A. To manage database connections efficiently

B. To collect and expose application metrics like counters and timers

C. To handle user authentication and authorization

D. To serve static web content like images and CSS

Solution

1. Step 1: Understand Micrometer's role

   Micrometer is designed to collect metrics such as counters, timers, and gauges to monitor app performance.

2. Step 2: Compare with other options

   Options B, C, and D relate to database, security, and web content, which are not Micrometer's focus.

3. Final Answer:

   To collect and expose application metrics like counters and timers -> Option B

4. Quick Check:

   Micrometer = Metrics collection [OK]

Hint: Micrometer is for metrics, not security or database [OK]

Common Mistakes:

• Confusing Micrometer with security or database tools
• Thinking Micrometer serves static files
• Assuming Micrometer manages app logic

2. Which of the following is the correct way to create a counter metric using Micrometer in Spring Boot?

easy

A. Counter counter = Counter.builder("my.counter").register(meterRegistry);

B. Counter counter = new Counter("my.counter");

C. Counter counter = meterRegistry.createCounter("my.counter");

D. Counter counter = Counter.create("my.counter");

Solution

1. Step 1: Recall Micrometer counter creation syntax

   Micrometer uses builder pattern: Counter.builder(name).register(meterRegistry) to create counters.

2. Step 2: Check other options for correctness

   Options B, C, and D use incorrect constructors or methods not available in Micrometer.

3. Final Answer:

   Counter counter = Counter.builder("my.counter").register(meterRegistry); -> Option A

4. Quick Check:

   Use builder().register() to create counters [OK]

Hint: Use builder() and register() to create metrics [OK]

Common Mistakes:

• Trying to instantiate Counter with new keyword
• Using non-existent createCounter method
• Missing register() call after builder()

3. Given the following code snippet in a Spring Boot app using Micrometer:

Counter counter = Counter.builder("requests.count").register(meterRegistry);
counter.increment();
counter.increment(2);

What will be the value of the counter after these calls?

medium

A. 3

B. 2

C. 0

D. 1

Solution

1. Step 1: Analyze the increment calls

   The first call increments the counter by 1, the second increments by 2.

2. Step 2: Calculate total increments

   Total increments = 1 + 2 = 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   1 + 2 = 3 increments [OK]

Hint: Add all increment values to get total count [OK]

Common Mistakes:

• Ignoring the second increment call
• Assuming increment() resets counter
• Confusing increment() with set()

4. Consider this Spring Boot code snippet using Micrometer:

Counter counter = Counter.builder("api.calls").register(meterRegistry);
counter.increment(-1);

What is the issue with this code?

medium

A. meterRegistry is not initialized properly

B. Counter names cannot contain dots

C. Counters cannot be incremented by negative values; this will throw an exception

D. increment() method does not exist on Counter

Solution

1. Step 1: Understand Counter increment rules

   Counters only allow positive increments; negative values cause errors.

2. Step 2: Validate other options

   Counter names with dots are allowed, meterRegistry is assumed valid, and increment() exists.

3. Final Answer:

   Counters cannot be incremented by negative values; this will throw an exception -> Option C

4. Quick Check:

   Counter increments must be positive [OK]

Hint: Counters only accept positive increments [OK]

Common Mistakes:

• Trying to decrement counters with negative increments
• Thinking dots in metric names are invalid
• Assuming increment() method is missing

5. You want to measure the duration of a method execution in a Spring Boot app using Micrometer. Which approach correctly uses a Timer to record the time taken by a method processData()?

hard

A. Timer timer = new Timer("process.time");
timer.start();
processData();
timer.stop();

B. Timer timer = Timer.create("process.time");
timer.record(processData());

C. meterRegistry.timer("process.time").start();
processData();
meterRegistry.timer("process.time").stop();

D. Timer timer = Timer.builder("process.time").register(meterRegistry);
timer.record(() -> processData());

Solution

1. Step 1: Identify correct Timer usage in Micrometer

   Micrometer uses Timer.builder(name).register() and timer.record(Runnable) to measure durations.

2. Step 2: Check other options for errors

   Options A, C, and D use invalid constructors or methods not supported by Micrometer.

3. Final Answer:

   Timer timer = Timer.builder("process.time").register(meterRegistry); timer.record(() -> processData()); -> Option D

4. Quick Check:

   Use Timer.builder().register() and record() for timing [OK]

Hint: Use timer.record(() -> method()) to measure duration [OK]

Common Mistakes:

• Trying to instantiate Timer with new or create()
• Calling start() and stop() manually on Timer
• Passing method call directly instead of lambda to record()