Metrics with Micrometer in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Micrometer in Spring Boot?

Micrometer is a library that helps collect and publish application metrics in Spring Boot. It acts like a bridge to many monitoring systems, making it easy to track app performance.

beginner

How do you create a custom counter metric using Micrometer?

You use the MeterRegistry to create a Counter. For example:
Counter counter = meterRegistry.counter("my_counter");
counter.increment(); This counts how many times an event happens.

intermediate

What is the role of MeterRegistry in Micrometer?

MeterRegistry is the main interface to register and manage all metrics like counters, gauges, and timers. It connects your app metrics to monitoring systems.

intermediate

Explain the difference between a Gauge and a Counter in Micrometer.

A Counter only goes up and counts events (like clicks). A Gauge measures a value that can go up or down (like current memory usage).

intermediate

How does Micrometer support multiple monitoring systems?

Micrometer uses 'binders' and 'exporters' to send metrics to many systems like Prometheus, Graphite, or New Relic without changing your code.

Which Micrometer component is used to register and manage metrics?

A MetricManager

B MetricCollector

C MeterRegistry

D MetricPublisher

MeterRegistry is the core interface to register and manage metrics in Micrometer.

What type of metric should you use to count how many times an event happens?

A Histogram

B Gauge

C Timer

D Counter

A Counter only increases and is used to count events.

Which of these metrics can go up and down in value?

A Counter

B Gauge

C Timer

D Summary

A Gauge measures values that can increase or decrease, like current temperature.

How does Micrometer send metrics to different monitoring systems?

A Using binders and exporters

B By rewriting code for each system

C Only supports Prometheus

D Using database triggers

Micrometer uses binders and exporters to support many monitoring systems without code changes.

In Spring Boot, how do you typically get access to MeterRegistry?

A By injecting it as a bean

B By reading from a config file

C By creating a new instance manually

D By calling a static method

MeterRegistry is injected as a bean in Spring Boot for easy use.

Describe how you would add a custom counter metric in a Spring Boot app using Micrometer.

Think about how you get MeterRegistry and how to use it to count events.

Explain the difference between a Gauge and a Counter metric and give an example of when to use each.

Consider if the value changes only up or both ways.

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()