Implement Health Check for Microservices Observability (#2695)

health-check/README.md

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+---
+title: Health Check Pattern
+category: Performance
+language: en
+tag:
+  - Microservices
+  - Resilience
+  - Observability
+---
+
+# Health Check Pattern
+
+## Also known as
+Health Monitoring, Service Health Check
+
+## Intent
+To ensure the stability and resilience of services in a microservices architecture by providing a way to monitor and diagnose their health.
+
+## Explanation
+In microservices architecture, it's critical to continuously check the health of individual services. The Health Check Pattern is a mechanism for microservices to expose their health status. This pattern is implemented by including a health check endpoint in microservices that returns the service's current state. This is vital for maintaining system resilience and operational readiness.
+
+## Class Diagram
+![alt text](./etc/health-check.png "Health Check")
+
+## Applicability
+Use the Health Check Pattern when:
+- You have an application composed of multiple services and need to monitor the health of each service individually.
+- You want to implement automatic service recovery or replacement based on health status.
+- You are employing orchestration or automation tools that rely on health checks to manage service instances.
+
+## Tutorials
+- Implementing Health Checks in Java using Spring Boot Actuator.
+
+## Known Uses
+- Kubernetes Liveness and Readiness Probes
+- AWS Elastic Load Balancing Health Checks
+- Spring Boot Actuator
+
+## Consequences
+**Pros:**
+- Enhances the fault tolerance of the system by detecting failures and enabling quick recovery.
+- Improves the visibility of system health for operational monitoring and alerting.
+
+**Cons:**
+- Adds complexity to service implementation.
+- Requires a strategy to handle cascading failures when dependent services are unhealthy.
+
+## Related Patterns
+- Circuit Breaker
+- Retry Pattern
+- Timeout Pattern
+
+## Credits
+Inspired by the Health Check API pattern from [microservices.io](https://microservices.io/patterns/observability/health-check-api.html) and the issue [#2695](https://github.com/iluwatar/java-design-patterns/issues/2695) on iluwatar's Java design patterns repository.

health-check/etc/health-check.puml

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+@startuml
+
+!theme plain
+top to bottom direction
+skinparam linetype ortho
+
+class App {
+  + App(): 
+  + main(String[]): void
+}
+class AsynchronousHealthChecker {
+  + AsynchronousHealthChecker(): 
+  + performCheck(Supplier<Health>, long): CompletableFuture<Health>
+  - awaitTerminationWithTimeout(): boolean
+  + shutdown(): void
+}
+class CpuHealthIndicator {
+  + CpuHealthIndicator(): 
+  - processCpuLoadThreshold: double
+  - systemCpuLoadThreshold: double
+  - loadAverageThreshold: double
+  - osBean: OperatingSystemMXBean
+  - defaultWarningMessage: String
+  + init(): void
+  + health(): Health
+   defaultWarningMessage: String
+   osBean: OperatingSystemMXBean
+   loadAverageThreshold: double
+   processCpuLoadThreshold: double
+   systemCpuLoadThreshold: double
+}
+class CustomHealthIndicator {
+  + CustomHealthIndicator(AsynchronousHealthChecker, CacheManager, HealthCheckRepository): 
+  + evictHealthCache(): void
+  - check(): Health
+  + health(): Health
+}
+class DatabaseTransactionHealthIndicator {
+  + DatabaseTransactionHealthIndicator(HealthCheckRepository, AsynchronousHealthChecker, RetryTemplate): 
+  - retryTemplate: RetryTemplate
+  - healthCheckRepository: HealthCheckRepository
+  - timeoutInSeconds: long
+  - asynchronousHealthChecker: AsynchronousHealthChecker
+  + health(): Health
+   timeoutInSeconds: long
+   retryTemplate: RetryTemplate
+   healthCheckRepository: HealthCheckRepository
+   asynchronousHealthChecker: AsynchronousHealthChecker
+}
+class GarbageCollectionHealthIndicator {
+  + GarbageCollectionHealthIndicator(): 
+  - memoryUsageThreshold: double
+  + health(): Health
+   memoryPoolMxBeans: List<MemoryPoolMXBean>
+   garbageCollectorMxBeans: List<GarbageCollectorMXBean>
+   memoryUsageThreshold: double
+}
+class HealthCheck {
+  + HealthCheck(): 
+  - status: String
+  - id: Integer
+  + equals(Object): boolean
+  # canEqual(Object): boolean
+  + hashCode(): int
+  + toString(): String
+   id: Integer
+   status: String
+}
+class HealthCheckRepository {
+  + HealthCheckRepository(): 
+  + performTestTransaction(): void
+  + checkHealth(): Integer
+}
+class MemoryHealthIndicator {
+  + MemoryHealthIndicator(AsynchronousHealthChecker): 
+  + checkMemory(): Health
+  + health(): Health
+}
+class RetryConfig {
+  + RetryConfig(): 
+  + retryTemplate(): RetryTemplate
+}
+
+CustomHealthIndicator              "1" *-[#595959,plain]-> "healthChecker\n1" AsynchronousHealthChecker          
+CustomHealthIndicator              "1" *-[#595959,plain]-> "healthCheckRepository\n1" HealthCheckRepository              
+DatabaseTransactionHealthIndicator "1" *-[#595959,plain]-> "asynchronousHealthChecker\n1" AsynchronousHealthChecker          
+DatabaseTransactionHealthIndicator "1" *-[#595959,plain]-> "healthCheckRepository\n1" HealthCheckRepository              
+HealthCheckRepository               -[#595959,dashed]->  HealthCheck                        : "«create»"
+MemoryHealthIndicator              "1" *-[#595959,plain]-> "asynchronousHealthChecker\n1" AsynchronousHealthChecker          
+@enduml

health-check/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+
+    The MIT License
+    Copyright © 2014-2022 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>com.iluwatar</groupId>
+        <artifactId>java-design-patterns</artifactId>
+        <version>1.26.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>health-check</artifactId>
+
+    <dependencies>
+        <!-- Spring Boot Dependencies -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+
+        <!-- Spring Boot Actuator for health check -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-actuator</artifactId>
+        </dependency>
+
+        <!-- Spring Boot Data JPA for database access -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-data-jpa</artifactId>
+        </dependency>
+
+        <!-- Testing Dependencies -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+
+        <!-- Spring Retry for retrying failed database operations -->
+        <dependency>
+            <groupId>org.springframework.retry</groupId>
+            <artifactId>spring-retry</artifactId>
+        </dependency>
+
+
+        <!-- JUnit Jupiter Engine for testing -->
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+
+        <!-- Mockito for mocking in tests -->
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+
+        <!-- H2 for mocking database -->
+        <dependency>
+            <groupId>com.h2database</groupId>
+            <artifactId>h2</artifactId>
+            <scope>runtime</scope>
+        </dependency>
+
+        <!-- https://mvnrepository.com/artifact/org.assertj/assertj-core -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>3.24.2</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>io.rest-assured</groupId>
+            <artifactId>rest-assured</artifactId>
+            <scope>test</scope>
+        </dependency>
+
+
+    </dependencies>
+
+
+    <build>
+        <plugins>
+            <!-- Maven Assembly Plugin for creating a single distributable JAR -->
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>single</goal>
+                        </goals>
+                        <configuration>
+                            <descriptorRefs>
+                                <descriptorRef>jar-with-dependencies</descriptorRef>
+                            </descriptorRefs>
+                            <archive>
+                                <manifest>
+                                    <!-- Define the main class for the executable JAR -->
+                                    <mainClass>com.iluwatar.healthcheck.App</mainClass>
+                                </manifest>
+                            </archive>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+
+            <!-- Other plugins as needed -->
+
+        </plugins>
+    </build>
+</project>

health-check/src/main/java/com/iluwatar/health/check/App.java

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+package com.iluwatar.health.check;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.cache.annotation.EnableCaching;
+import org.springframework.scheduling.annotation.EnableScheduling;
+
+/**
+ * This application provides health check APIs for various aspects of the microservice architecture,
+ * including database transactions, garbage collection, and overall system health. These health
+ * checks are essential for monitoring the health and performance of the microservices and ensuring
+ * their availability and responsiveness. For more information about health checks and their role in
+ * microservice architectures, please refer to: [Microservices Health Checks
+ * API]('https://microservices.io/patterns/observability/health-check-api.html').
+ *
+ * @author ydoksanbir
+ */
+@EnableCaching
+@EnableScheduling
+@SpringBootApplication
+public class App {
+  /** Program entry point. */
+  public static void main(String[] args) {
+    SpringApplication.run(App.class, args);
+  }
+}