分布式系统设计
1.服务注册与发现
import java.util.*;
public class ServiceRegistry {
private Map<String, List<String>> services = new HashMap<>();
public void registerService(String serviceName, String serviceUrl) {
List<String> urls = services.computeIfAbsent(serviceName, k -> new ArrayList<>());
urls.add(serviceUrl);
services.put(serviceName, urls);
}
public List<String> getServiceUrl(String serviceName) {
return services.get(serviceName);
}
}
2.负载均衡
import java.util.*;
public class LoadBalancer {
private final ServiceRegistry serviceRegistry;
public LoadBalancer(ServiceRegistry serviceRegistry) {
this.serviceRegistry = serviceRegistry;
}
public String chooseServer(String serviceName) {
List<String> urls = serviceRegistry.getServiceUrl(serviceName);
if (urls.isEmpty()) {
throw new RuntimeException("No available service for " + serviceName);
}
Random random = new Random();
int randomIndex = random.nextInt(urls.size());
return urls.get(randomIndex);
}
}
3.容错
import java.util.*;
public class CircuitBreaker {
private final LoadBalancer loadBalancer;
private final int failureThreshold;
private final int timeout;
private int failureCount;
private long lastFailureTime;
public CircuitBreaker(LoadBalancer loadBalancer, int failureThreshold, int timeout) {
this.loadBalancer = loadBalancer;
this.failureThreshold = failureThreshold;
this.timeout = timeout;
this.failureCount = 0;
this.lastFailureTime = 0;
}
public String execute(String serviceName, String operation) {
String serverUrl = loadBalancer.chooseServer(serviceName);
if (isCircuitBreakerOpen()) {
throw new RuntimeException("Circuit breaker is open for " + serviceName);
}
try {
// Call the service operation
return callService(serverUrl, operation);
} catch (Exception ex) {
failureCount++;
lastFailureTime = System.currentTimeMillis();
if (isCircuitBreakerTripped()) {
throw new RuntimeException("Circuit breaker is tripped for " + serviceName);
}
throw ex;
}
}
private boolean isCircuitBreakerOpen() {
return failureCount >= failureThreshold && isTimeoutElapsed();
}
private boolean isCircuitBreakerTripped() {
return failureCount >= failureThreshold;
}
private boolean isTimeoutElapsed() {
return System.currentTimeMillis() - lastFailureTime > timeout;
}
private String callService(String serverUrl, String operation) {
// Call the service operation using HTTP or some other protocol
return "";
}
}
其中，isCircuitBreakerOpen是一个判断方法，用于判断一个开关是否打开。在分布式系统中，通常使用熔断器（Circuit Breaker）来实现容错机制。熔断器可以防止系统连锁故障，提高系统的可用性。当调用某个服务的失败次数达到一定的阈值后，熔断器会打开，表示该服务不可用，从而避免对该服务的继续调用。isCircuitBreakerOpen方法用于判断熔断器是否处于打开状态，如果熔断器打开，则不能再对该服务进行调用，需要等待一定的时间后再尝试重新调用服务。
