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pattern: Implement Health Check for Microservices Observability (#2695) (#2774)
* Add Health Check pattern implementation The commit introduces Health Check pattern, providing a series of health indicators for system performance and stability monitoring, including checks for system CPU load, process CPU load, database health, memory usage, and garbage collection metrics. It also includes asynchronous execution and caching mechanisms for health checks, and retry configurations for resilience. Implements health checking components as per issue #2695. * Test cases and javadoc for HealthEndpointIntegrationTest * Added more log to test case to see why it returns 503 * Change config values to see if the system High system CPU load is resolved or not in CI. * Fixes for test cases. * some fixes for Sonar. * some fixes for Sonar. ADDED HIGH_PROCESS_CPU_LOAD_MESSAGE_WITHOUT_PARAM ADDED HIGH_SYSTEM_CPU_LOAD_MESSAGE_WITHOUT_PARAM * Sonar fixes address "Define and throw a dedicated exception instead of using a generic one." added HealthCheckInterruptedException refactored CustomHealthIndicator * fixes checkstyle violation.
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‎health-check/README.md‎

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---
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title: Health Check Pattern
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category: Performance
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language: en
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tag:
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- Microservices
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- Resilience
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- Observability
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---
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# Health Check Pattern
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## Also known as
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Health Monitoring, Service Health Check
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## Intent
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To ensure the stability and resilience of services in a microservices architecture by providing a way to monitor and diagnose their health.
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## Explanation
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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.
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## Class Diagram
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![alt text](./etc/health-check.png "Health Check")
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## Applicability
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Use the Health Check Pattern when:
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- You have an application composed of multiple services and need to monitor the health of each service individually.
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- You want to implement automatic service recovery or replacement based on health status.
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- You are employing orchestration or automation tools that rely on health checks to manage service instances.
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## Tutorials
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- Implementing Health Checks in Java using Spring Boot Actuator.
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## Known Uses
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- Kubernetes Liveness and Readiness Probes
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- AWS Elastic Load Balancing Health Checks
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- Spring Boot Actuator
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## Consequences
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**Pros:**
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- Enhances the fault tolerance of the system by detecting failures and enabling quick recovery.
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- Improves the visibility of system health for operational monitoring and alerting.
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**Cons:**
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- Adds complexity to service implementation.
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- Requires a strategy to handle cascading failures when dependent services are unhealthy.
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## Related Patterns
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- Circuit Breaker
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- Retry Pattern
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- Timeout Pattern
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## Credits
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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.png‎

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‎health-check/etc/health-check.puml‎

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

‎health-check/pom.xml‎

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

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

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

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