一、IPing机制
IPing是一个主动探测服务节点存活的机制，通过判断服务节点的当前状态，设置节点的可用状态。只有当节点为可用时候才会作为负载均衡器的选取节点。
IPing有以下几种模式:
- DummyPing：默认返回true，即认为所有节点都可用，这也是单独使用Ribbon时的默认模式
- NIWSDiscoveryPing：借助Eureka服务发现机制获取节点状态。节点状态是UP，则认为是可用状态
- PingUrl：主动向服务节点发起一次http调用，对方有响应则认为节点是可用状态
- NoOpPing：返回true
- PingConstant：返回设置的常量值
二、IPing配置
（1）application.yaml配置
#单个服务设置
[service-name]: ribbon: NFLoadBalancerPingClassName: com.netflix.loadbalancer.DummyPing（2）代码配置
public class MicroRibbonConfig {@Beanpublic IPing microIPing(){return new DummyPing();}
}@RibbonClient(name = "micro-service", configuration = MicroRibbonConfig.class)
public class RibbonClientConfig {}
三、IPing模式实现
（1）DummyPing
public class DummyPing extends AbstractLoadBalancerPing {public DummyPing() {}public boolean isAlive(Server server) {return true;}@Overridepublic void initWithNiwsConfig(IClientConfig clientConfig) {}
}public abstract class AbstractLoadBalancerPing implements IPing, IClientConfigAware{AbstractLoadBalancer lb;@Overridepublic boolean isAlive(Server server) {return true;}public void setLoadBalancer(AbstractLoadBalancer lb){this.lb = lb;}public AbstractLoadBalancer getLoadBalancer(){return lb;}}（2）PingUrl
public class PingUrl implements IPing {private static final Logger LOGGER = LoggerFactory.getLogger(PingUrl.class);String pingAppendString = "";boolean isSecure = false;String expectedContent = null;/*** Send one ping only.** Well, send what you need to determine whether or not the* server is still alive. Should return within a "reasonable"* time.*/public PingUrl() {}public PingUrl(boolean isSecure, String pingAppendString) {this.isSecure = isSecure;this.pingAppendString = (pingAppendString != null) ? pingAppendString : "";}public void setPingAppendString(String pingAppendString) {this.pingAppendString = (pingAppendString != null) ? pingAppendString : "";}public String getPingAppendString() {return pingAppendString;}public boolean isSecure() {return isSecure;}/*** Should the Secure protocol be used to Ping* @param isSecure*/public void setSecure(boolean isSecure) {this.isSecure = isSecure;}public String getExpectedContent() {return expectedContent;}/*** Is there a particular content you are hoping to see?* If so -set this here.* for e.g. the WCS server sets the content body to be 'true'* Please be advised that this content should match the actual * content exactly for this to work. Else yo may get false status.* @param expectedContent*/public void setExpectedContent(String expectedContent) {this.expectedContent = expectedContent;}public boolean isAlive(Server server) {String urlStr = "";if (isSecure){urlStr = "https://";}else{urlStr = "http://";}urlStr += server.getId();urlStr += getPingAppendString();boolean isAlive = false;HttpClient httpClient = new DefaultHttpClient();HttpUriRequest getRequest = new HttpGet(urlStr);String content=null;try {HttpResponse response = httpClient.execute(getRequest);content = EntityUtils.toString(response.getEntity());isAlive = (response.getStatusLine().getStatusCode() == 200);if (getExpectedContent()!=null){LOGGER.debug("content:" + content);if (content == null){isAlive = false;}else{if (content.equals(getExpectedContent())){isAlive = true;}else{isAlive = false;}}}} catch (IOException e) {e.printStackTrace();}finally{// Release the connection.getRequest.abort();}return isAlive;}public static void main(String[] args){PingUrl p = new PingUrl(false,"/cs/hostRunning");p.setExpectedContent("true");Server s = new Server("ec2-75-101-231-85.compute-1.amazonaws.com", 7101);boolean isAlive = p.isAlive(s);System.out.println("isAlive:" + isAlive);}
}（3）PingConstant
public class PingConstant implements IPing {boolean constant = true;public void setConstant(String constantStr) {constant = (constantStr != null) && (constantStr.toLowerCase().equals("true"));}public void setConstant(boolean constant) {this.constant = constant;}public boolean getConstant() {return constant;}public boolean isAlive(Server server) {return constant;}
}
（4）NoOpPing
public class NoOpPing implements IPing {@Overridepublic boolean isAlive(Server server) {return true;}}
