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docs: updates to several patterns

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Ilkka Seppälä committed 2024-05-28 19:46:39 +03:00
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circuit-breaker/README.md
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@@ -95,6 +95,57 @@ LOGGER.info(monitoringService.delayedServiceResponse());
LOGGER.info(delayedServiceCircuitBreaker.getState());
```
6. **Full example**
```java
public static void main(String[] args) {
var serverStartTime = System.nanoTime();
var delayedService = new DelayedRemoteService(serverStartTime, 5);
var delayedServiceCircuitBreaker = new DefaultCircuitBreaker(delayedService, 3000, 2,
2000 * 1000 * 1000);
var quickService = new QuickRemoteService();
var quickServiceCircuitBreaker = new DefaultCircuitBreaker(quickService, 3000, 2,
2000 * 1000 * 1000);
//Create an object of monitoring service which makes both local and remote calls
var monitoringService = new MonitoringService(delayedServiceCircuitBreaker,
quickServiceCircuitBreaker);
//Fetch response from local resource
LOGGER.info(monitoringService.localResourceResponse());
//Fetch response from delayed service 2 times, to meet the failure threshold
LOGGER.info(monitoringService.delayedServiceResponse());
LOGGER.info(monitoringService.delayedServiceResponse());
//Fetch current state of delayed service circuit breaker after crossing failure threshold limit
//which is OPEN now
LOGGER.info(delayedServiceCircuitBreaker.getState());
//Meanwhile, the delayed service is down, fetch response from the healthy quick service
LOGGER.info(monitoringService.quickServiceResponse());
LOGGER.info(quickServiceCircuitBreaker.getState());
//Wait for the delayed service to become responsive
try {
LOGGER.info("Waiting for delayed service to become responsive");
Thread.sleep(5000);
} catch (InterruptedException e) {
LOGGER.error("An error occurred: ", e);
}
//Check the state of delayed circuit breaker, should be HALF_OPEN
LOGGER.info(delayedServiceCircuitBreaker.getState());
//Fetch response from delayed service, which should be healthy by now
LOGGER.info(monitoringService.delayedServiceResponse());
//As successful response is fetched, it should be CLOSED again.
LOGGER.info(delayedServiceCircuitBreaker.getState());
}
```
Summary of the example
- Initialize the Circuit Breaker with parameters: `timeout`, `failureThreshold`, and `retryTimePeriod`.
@@ -104,12 +155,23 @@ Summary of the example
- After the retry timeout, transition to the `half-open` state to test the service.
- On success in `half-open` state, transition back to `closed`. On failure, return to `open`.
Program output:
```
16:59:19.767 [main] INFO com.iluwatar.circuitbreaker.App -- Local Service is working
16:59:19.769 [main] INFO com.iluwatar.circuitbreaker.App -- Delayed service is down
16:59:19.769 [main] INFO com.iluwatar.circuitbreaker.App -- Delayed service is down
16:59:19.769 [main] INFO com.iluwatar.circuitbreaker.App -- OPEN
16:59:19.769 [main] INFO com.iluwatar.circuitbreaker.App -- Quick Service is working
16:59:19.769 [main] INFO com.iluwatar.circuitbreaker.App -- CLOSED
16:59:19.769 [main] INFO com.iluwatar.circuitbreaker.App -- Waiting for delayed service to become responsive
16:59:24.779 [main] INFO com.iluwatar.circuitbreaker.App -- HALF_OPEN
16:59:24.780 [main] INFO com.iluwatar.circuitbreaker.App -- Delayed service is working
16:59:24.780 [main] INFO com.iluwatar.circuitbreaker.App -- CLOSED
```
This example demonstrates how the Circuit Breaker pattern can help maintain application stability and resilience by managing remote service failures.
## Class diagram
![Circuit Breaker](./etc/circuit-breaker.urm.png "Circuit Breaker class diagram")
## Applicability
* In distributed systems where individual service failures can lead to cascading system-wide failures