mirror of
https://github.com/tiennm99/java-design-patterns.git
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docs: add editorconfig + formatting
This commit is contained in:
Ilkka Seppälä
+196
-197
@@ -3,9 +3,9 @@ title: Circuit Breaker
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category: Resilience
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language: en
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tag:
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- Cloud distributed
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- Fault tolerance
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- Microservices
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- Cloud distributed
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- Fault tolerance
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- Microservices
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---
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## Also known as
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@@ -28,10 +28,9 @@ Real world example
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> services is slow or not responding successfully, our application will try to fetch response from
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> the remote service using multiple threads/processes, soon all of them will hang (also called
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> [thread starvation](https://en.wikipedia.org/wiki/Starvation_(computer_science))) causing our entire web application
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> to crash. We should be able to detect
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> this situation and show the user an appropriate message so that he/she can explore other parts of
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> the app unaffected by the remote service failure. Meanwhile, the other services that are working
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> normally, should keep functioning unaffected by this failure.
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> to crash. We should be able to detect this situation and show the user an appropriate message so that he/she can
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> explore other parts of the app unaffected by the remote serv'ice failure. Meanwhile, the other services that are
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> working normally, should keep functioning unaffected by this failure.
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In plain words
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@@ -62,59 +61,59 @@ In terms of code, the end user application is:
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@Slf4j
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public class App {
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private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
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private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
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/**
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* Program entry point.
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*
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* @param args command line args
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*/
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public static void main(String[] args) {
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/**
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* Program entry point.
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*
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* @param args command line args
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*/
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public static void main(String[] args) {
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var serverStartTime = System.nanoTime();
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var serverStartTime = System.nanoTime();
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var delayedService = new DelayedRemoteService(serverStartTime, 5);
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var delayedServiceCircuitBreaker = new DefaultCircuitBreaker(delayedService, 3000, 2,
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2000 * 1000 * 1000);
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var delayedService = new DelayedRemoteService(serverStartTime, 5);
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var delayedServiceCircuitBreaker = new DefaultCircuitBreaker(delayedService, 3000, 2,
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2000 * 1000 * 1000);
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var quickService = new QuickRemoteService();
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var quickServiceCircuitBreaker = new DefaultCircuitBreaker(quickService, 3000, 2,
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2000 * 1000 * 1000);
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var quickService = new QuickRemoteService();
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var quickServiceCircuitBreaker = new DefaultCircuitBreaker(quickService, 3000, 2,
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2000 * 1000 * 1000);
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//Create an object of monitoring service which makes both local and remote calls
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var monitoringService = new MonitoringService(delayedServiceCircuitBreaker,
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quickServiceCircuitBreaker);
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//Create an object of monitoring service which makes both local and remote calls
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var monitoringService = new MonitoringService(delayedServiceCircuitBreaker,
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quickServiceCircuitBreaker);
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//Fetch response from local resource
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LOGGER.info(monitoringService.localResourceResponse());
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//Fetch response from local resource
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LOGGER.info(monitoringService.localResourceResponse());
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//Fetch response from delayed service 2 times, to meet the failure threshold
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LOGGER.info(monitoringService.delayedServiceResponse());
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LOGGER.info(monitoringService.delayedServiceResponse());
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//Fetch response from delayed service 2 times, to meet the failure threshold
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LOGGER.info(monitoringService.delayedServiceResponse());
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LOGGER.info(monitoringService.delayedServiceResponse());
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//Fetch current state of delayed service circuit breaker after crossing failure threshold limit
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//which is OPEN now
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LOGGER.info(delayedServiceCircuitBreaker.getState());
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//Fetch current state of delayed service circuit breaker after crossing failure threshold limit
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//which is OPEN now
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LOGGER.info(delayedServiceCircuitBreaker.getState());
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//Meanwhile, the delayed service is down, fetch response from the healthy quick service
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LOGGER.info(monitoringService.quickServiceResponse());
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LOGGER.info(quickServiceCircuitBreaker.getState());
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//Meanwhile, the delayed service is down, fetch response from the healthy quick service
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LOGGER.info(monitoringService.quickServiceResponse());
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LOGGER.info(quickServiceCircuitBreaker.getState());
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//Wait for the delayed service to become responsive
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try {
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LOGGER.info("Waiting for delayed service to become responsive");
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Thread.sleep(5000);
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} catch (InterruptedException e) {
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LOGGER.error("An error occurred: ", e);
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//Wait for the delayed service to become responsive
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try {
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LOGGER.info("Waiting for delayed service to become responsive");
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Thread.sleep(5000);
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} catch (InterruptedException e) {
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LOGGER.error("An error occurred: ", e);
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}
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//Check the state of delayed circuit breaker, should be HALF_OPEN
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LOGGER.info(delayedServiceCircuitBreaker.getState());
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//Fetch response from delayed service, which should be healthy by now
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LOGGER.info(monitoringService.delayedServiceResponse());
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//As successful response is fetched, it should be CLOSED again.
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LOGGER.info(delayedServiceCircuitBreaker.getState());
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}
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//Check the state of delayed circuit breaker, should be HALF_OPEN
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LOGGER.info(delayedServiceCircuitBreaker.getState());
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//Fetch response from delayed service, which should be healthy by now
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LOGGER.info(monitoringService.delayedServiceResponse());
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//As successful response is fetched, it should be CLOSED again.
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LOGGER.info(delayedServiceCircuitBreaker.getState());
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}
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}
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```
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@@ -123,45 +122,45 @@ The monitoring service:
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```java
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public class MonitoringService {
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private final CircuitBreaker delayedService;
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private final CircuitBreaker delayedService;
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private final CircuitBreaker quickService;
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private final CircuitBreaker quickService;
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public MonitoringService(CircuitBreaker delayedService, CircuitBreaker quickService) {
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this.delayedService = delayedService;
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this.quickService = quickService;
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}
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//Assumption: Local service won't fail, no need to wrap it in a circuit breaker logic
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public String localResourceResponse() {
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return "Local Service is working";
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}
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/**
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* Fetch response from the delayed service (with some simulated startup time).
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*
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* @return response string
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*/
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public String delayedServiceResponse() {
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try {
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return this.delayedService.attemptRequest();
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} catch (RemoteServiceException e) {
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return e.getMessage();
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public MonitoringService(CircuitBreaker delayedService, CircuitBreaker quickService) {
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this.delayedService = delayedService;
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this.quickService = quickService;
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}
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}
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/**
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* Fetches response from a healthy service without any failure.
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*
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* @return response string
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*/
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public String quickServiceResponse() {
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try {
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return this.quickService.attemptRequest();
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} catch (RemoteServiceException e) {
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return e.getMessage();
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//Assumption: Local service won't fail, no need to wrap it in a circuit breaker logic
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public String localResourceResponse() {
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return "Local Service is working";
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}
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/**
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* Fetch response from the delayed service (with some simulated startup time).
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*
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* @return response string
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*/
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public String delayedServiceResponse() {
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try {
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return this.delayedService.attemptRequest();
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} catch (RemoteServiceException e) {
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return e.getMessage();
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}
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}
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/**
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* Fetches response from a healthy service without any failure.
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*
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* @return response string
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*/
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public String quickServiceResponse() {
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try {
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return this.quickService.attemptRequest();
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} catch (RemoteServiceException e) {
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return e.getMessage();
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}
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}
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}
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}
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```
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@@ -171,128 +170,128 @@ remote (costly) service in a circuit breaker object, which prevents faults as fo
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```java
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public class DefaultCircuitBreaker implements CircuitBreaker {
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private final long timeout;
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private final long retryTimePeriod;
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private final RemoteService service;
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long lastFailureTime;
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private String lastFailureResponse;
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int failureCount;
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private final int failureThreshold;
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private State state;
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// Future time offset, in nanoseconds
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private final long futureTime = 1_000_000_000_000L;
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private final long timeout;
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private final long retryTimePeriod;
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private final RemoteService service;
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long lastFailureTime;
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private String lastFailureResponse;
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int failureCount;
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private final int failureThreshold;
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private State state;
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// Future time offset, in nanoseconds
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private final long futureTime = 1_000_000_000_000L;
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/**
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* Constructor to create an instance of Circuit Breaker.
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*
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* @param timeout Timeout for the API request. Not necessary for this simple example
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* @param failureThreshold Number of failures we receive from the depended service before changing
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* state to 'OPEN'
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* @param retryTimePeriod Time period after which a new request is made to remote service for
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* status check.
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*/
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DefaultCircuitBreaker(RemoteService serviceToCall, long timeout, int failureThreshold,
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long retryTimePeriod) {
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this.service = serviceToCall;
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// We start in a closed state hoping that everything is fine
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this.state = State.CLOSED;
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this.failureThreshold = failureThreshold;
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// Timeout for the API request.
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// Used to break the calls made to remote resource if it exceeds the limit
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this.timeout = timeout;
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this.retryTimePeriod = retryTimePeriod;
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//An absurd amount of time in future which basically indicates the last failure never happened
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this.lastFailureTime = System.nanoTime() + futureTime;
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this.failureCount = 0;
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}
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// Reset everything to defaults
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@Override
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public void recordSuccess() {
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this.failureCount = 0;
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this.lastFailureTime = System.nanoTime() + futureTime;
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this.state = State.CLOSED;
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}
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@Override
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public void recordFailure(String response) {
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failureCount = failureCount + 1;
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this.lastFailureTime = System.nanoTime();
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// Cache the failure response for returning on open state
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this.lastFailureResponse = response;
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}
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// Evaluate the current state based on failureThreshold, failureCount and lastFailureTime.
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protected void evaluateState() {
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if (failureCount >= failureThreshold) { //Then something is wrong with remote service
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if ((System.nanoTime() - lastFailureTime) > retryTimePeriod) {
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//We have waited long enough and should try checking if service is up
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state = State.HALF_OPEN;
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} else {
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//Service would still probably be down
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state = State.OPEN;
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}
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} else {
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//Everything is working fine
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state = State.CLOSED;
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/**
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* Constructor to create an instance of Circuit Breaker.
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*
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* @param timeout Timeout for the API request. Not necessary for this simple example
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* @param failureThreshold Number of failures we receive from the depended service before changing
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* state to 'OPEN'
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* @param retryTimePeriod Time period after which a new request is made to remote service for
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* status check.
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*/
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DefaultCircuitBreaker(RemoteService serviceToCall, long timeout, int failureThreshold,
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long retryTimePeriod) {
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this.service = serviceToCall;
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// We start in a closed state hoping that everything is fine
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this.state = State.CLOSED;
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this.failureThreshold = failureThreshold;
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// Timeout for the API request.
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// Used to break the calls made to remote resource if it exceeds the limit
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this.timeout = timeout;
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this.retryTimePeriod = retryTimePeriod;
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//An absurd amount of time in future which basically indicates the last failure never happened
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this.lastFailureTime = System.nanoTime() + futureTime;
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this.failureCount = 0;
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}
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}
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@Override
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public String getState() {
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evaluateState();
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return state.name();
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}
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// Reset everything to defaults
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@Override
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public void recordSuccess() {
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this.failureCount = 0;
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this.lastFailureTime = System.nanoTime() + futureTime;
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this.state = State.CLOSED;
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}
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/**
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* Break the circuit beforehand if it is known service is down Or connect the circuit manually if
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* service comes online before expected.
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*
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* @param state State at which circuit is in
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*/
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@Override
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public void setState(State state) {
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this.state = state;
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switch (state) {
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case OPEN -> {
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this.failureCount = failureThreshold;
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@Override
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public void recordFailure(String response) {
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failureCount = failureCount + 1;
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this.lastFailureTime = System.nanoTime();
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}
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case HALF_OPEN -> {
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this.failureCount = failureThreshold;
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this.lastFailureTime = System.nanoTime() - retryTimePeriod;
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}
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default -> this.failureCount = 0;
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// Cache the failure response for returning on open state
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this.lastFailureResponse = response;
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}
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}
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/**
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* Executes service call.
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*
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* @return Value from the remote resource, stale response or a custom exception
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*/
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@Override
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public String attemptRequest() throws RemoteServiceException {
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evaluateState();
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if (state == State.OPEN) {
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// return cached response if the circuit is in OPEN state
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return this.lastFailureResponse;
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} else {
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// Make the API request if the circuit is not OPEN
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try {
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//In a real application, this would be run in a thread and the timeout
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//parameter of the circuit breaker would be utilized to know if service
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//is working. Here, we simulate that based on server response itself
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var response = service.call();
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// Yay!! the API responded fine. Let's reset everything.
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recordSuccess();
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return response;
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} catch (RemoteServiceException ex) {
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recordFailure(ex.getMessage());
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throw ex;
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}
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// Evaluate the current state based on failureThreshold, failureCount and lastFailureTime.
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protected void evaluateState() {
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if (failureCount >= failureThreshold) { //Then something is wrong with remote service
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if ((System.nanoTime() - lastFailureTime) > retryTimePeriod) {
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//We have waited long enough and should try checking if service is up
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state = State.HALF_OPEN;
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} else {
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//Service would still probably be down
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state = State.OPEN;
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}
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} else {
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//Everything is working fine
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state = State.CLOSED;
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}
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}
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@Override
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public String getState() {
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evaluateState();
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return state.name();
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}
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/**
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* Break the circuit beforehand if it is known service is down Or connect the circuit manually if
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* service comes online before expected.
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*
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* @param state State at which circuit is in
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*/
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@Override
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public void setState(State state) {
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this.state = state;
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switch (state) {
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case OPEN -> {
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this.failureCount = failureThreshold;
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this.lastFailureTime = System.nanoTime();
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}
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case HALF_OPEN -> {
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this.failureCount = failureThreshold;
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this.lastFailureTime = System.nanoTime() - retryTimePeriod;
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}
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default -> this.failureCount = 0;
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}
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}
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/**
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* Executes service call.
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*
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* @return Value from the remote resource, stale response or a custom exception
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*/
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@Override
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public String attemptRequest() throws RemoteServiceException {
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evaluateState();
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if (state == State.OPEN) {
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// return cached response if the circuit is in OPEN state
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return this.lastFailureResponse;
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} else {
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// Make the API request if the circuit is not OPEN
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try {
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//In a real application, this would be run in a thread and the timeout
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//parameter of the circuit breaker would be utilized to know if service
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//is working. Here, we simulate that based on server response itself
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var response = service.call();
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// Yay!! the API responded fine. Let's reset everything.
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recordSuccess();
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return response;
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} catch (RemoteServiceException ex) {
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recordFailure(ex.getMessage());
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throw ex;
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}
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}
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}
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}
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}
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```
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Reference in New Issue
Block a user