Spring Cloud中国社区博客

深入理解Ribbon

什么是Ribbon

Ribbon是Netflix公司开源的一个负载均衡的项目,它属于上述的第二种,是一个客户端负载均衡器,运行在客户端上。它是一个经过了云端测试的IPC库,可以很好地控制HTTP和TCP客户端的一些行为。 Feign已经默认使用了Ribbon。

  • 负载均衡
  • 容错
  • 多协议(HTTP,TCP,UDP)支持异步和反应模型
  • 缓存和批处理

RestTemplate和Ribbon相结合

Ribbon在Netflix组件是非常重要的一个组件,在Zuul中使用Ribbon做负载均衡,以及Feign组件的结合等。在Spring Cloud 中,作为开发中,做的最多的可能是将RestTemplate和Ribbon相结合,你可能会这样写:

1
2
3
4
5
6
7
8
@Configuration
public class RibbonConfig {
@Bean
@LoadBalanced
RestTemplate restTemplate() {
return new RestTemplate();
}
}

消费另外一个的服务的接口,差不多是这样的:

1
2
3
4
5
6
7
8
9
@Service
public class RibbonService {
@Autowired
RestTemplate restTemplate;
public String hi(String name) {
return restTemplate.getForObject("http://eureka-client/hi?name="+name,String.class);
}
}

深入理解Ribbon

LoadBalancerClient

在Riibon中一个非常重要的组件为LoadBalancerClient,它作为负载均衡的一个客户端。它在spring-cloud-commons包下:
的LoadBalancerClient是一个接口,它继承ServiceInstanceChooser,它的实现类是RibbonLoadBalancerClient,这三者之间的关系如下图:

image.png

其中LoadBalancerClient接口,有如下三个方法,其中excute()为执行请求,reconstructURI()用来重构url:

1
2
3
4
5
6
public interface LoadBalancerClient extends ServiceInstanceChooser {
<T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException;
<T> T execute(String serviceId, ServiceInstance serviceInstance, LoadBalancerRequest<T> request) throws IOException;
URI reconstructURI(ServiceInstance instance, URI original);
}

ServiceInstanceChooser接口,主要有一个方法,用来根据serviceId来获取ServiceInstance,代码如下:

1
2
3
4
public interface ServiceInstanceChooser {
ServiceInstance choose(String serviceId);
}

LoadBalancerClient的实现类为RibbonLoadBalancerClient,这个类是非常重要的一个类,最终的负载均衡的请求处理,由它来执行。它的部分源码如下:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
public class RibbonLoadBalancerClient implements LoadBalancerClient {
...//省略代码
@Override
public ServiceInstance choose(String serviceId) {
Server server = getServer(serviceId);
if (server == null) {
return null;
}
return new RibbonServer(serviceId, server, isSecure(server, serviceId),
serverIntrospector(serviceId).getMetadata(server));
}
protected Server getServer(String serviceId) {
return getServer(getLoadBalancer(serviceId));
}
protected Server getServer(ILoadBalancer loadBalancer) {
if (loadBalancer == null) {
return null;
}
return loadBalancer.chooseServer("default"); // TODO: better handling of key
}
protected ILoadBalancer getLoadBalancer(String serviceId) {
return this.clientFactory.getLoadBalancer(serviceId);
}
...//省略代码

在RibbonLoadBalancerClient的源码中,其中choose()方法是选择具体服务实例的一个方法。该方法通过getServer()方法去获取实例,经过源码跟踪,最终交给了ILoadBalancer类去选择服务实例。

ILoadBalancer在ribbon-loadbalancer的jar包下,它是定义了实现软件负载均衡的一个接口,它需要一组可供选择的服务注册列表信息,以及根据特定方法去选择服务,它的源码如下 :

1
2
3
4
5
6
7
8
public interface ILoadBalancer {
public void addServers(List<Server> newServers);
public Server chooseServer(Object key);
public void markServerDown(Server server);
public List<Server> getReachableServers();
public List<Server> getAllServers();
}

其中,addServers()方法是添加一个Server集合;chooseServer()方法是根据key去获取Server;markServerDown()方法用来标记某个服务下线;getReachableServers()获取可用的Server集合;getAllServers()获取所有的Server集合。

DynamicServerListLoadBalancer

它的继承类为BaseLoadBalancer,它的实现类为DynamicServerListLoadBalancer,这三者之间的关系如下:

image.png

查看上述三个类的源码,可用发现,配置以下信息,IClientConfig、IRule、IPing、ServerList、ServerListFilter和ILoadBalancer,查看BaseLoadBalancer类,它默认的情况下,实现了以下配置:

  • IClientConfig ribbonClientConfig: DefaultClientConfigImpl配置
  • IRule ribbonRule: RoundRobinRule 路由策略
  • IPing ribbonPing: DummyPing
  • ServerList ribbonServerList: ConfigurationBasedServerList
  • ServerListFilter ribbonServerListFilter: ZonePreferenceServerListFilter
  • ILoadBalancer ribbonLoadBalancer: ZoneAwareLoadBalancer

IClientConfig 用于对客户端或者负载均衡的配置,它的默认实现类为DefaultClientConfigImpl。

IRule用于复杂均衡的策略,它有三个方法,其中choose()是根据key 来获取server,setLoadBalancer()和getLoadBalancer()是用来设置和获取ILoadBalancer的,它的源码如下:

1
2
3
4
5
6
7
8
public interface IRule{
public Server choose(Object key);
public void setLoadBalancer(ILoadBalancer lb);
public ILoadBalancer getLoadBalancer();
}

IRule有很多默认的实现类,这些实现类根据不同的算法和逻辑来处理负载均衡。Ribbon实现的IRule有一下。在大多数情况下,这些默认的实现类是可以满足需求的,如果有特性的需求,可以自己实现。

  • BestAvailableRule 选择最小请求数
  • ClientConfigEnabledRoundRobinRule 轮询

  • RandomRule 随机选择一个server

  • RoundRobinRule 轮询选择server
  • RetryRule 根据轮询的方式重试
  • WeightedResponseTimeRule 根据响应时间去分配一个weight ,weight越低,被选择的可能性就越低
  • ZoneAvoidanceRule 根据server的zone区域和可用性来轮询选择

image.png

IPing是用来想server发生”ping”,来判断该server是否有响应,从而判断该server是否可用。它有一个isAlive()方法,它的源码如下:

1
2
3
public interface IPing {
public boolean isAlive(Server server);
}

IPing的实现类有PingUrl、PingConstant、NoOpPing、DummyPing和NIWSDiscoveryPing。它门之间的关系如下:

image.png

  • PingUrl 真实的去ping 某个url,判断其是否alive
  • PingConstant 固定返回某服务是否可用,默认返回true,即可用
  • NoOpPing 不去ping,直接返回true,即可用。
  • DummyPing 直接返回true,并实现了initWithNiwsConfig方法。
  • NIWSDiscoveryPing,根据DiscoveryEnabledServer的InstanceInfo的InstanceStatus去判断,如果为InstanceStatus.UP,则为可用,否则不可用。

ServerList是定义获取所有的server的注册列表信息的接口,它的代码如下:

1
2
3
4
5
6
public interface ServerList<T extends Server> {
public List<T> getInitialListOfServers();
public List<T> getUpdatedListOfServers();
}

ServerListFilter接口,定于了可根据配置去过滤或者根据特性动态获取符合条件的server列表的方法,代码如下:

1
2
3
4
5
public interface ServerListFilter<T extends Server> {
public List<T> getFilteredListOfServers(List<T> servers);
}

阅读DynamicServerListLoadBalancer的源码,DynamicServerListLoadBalancer的构造函数中有个initWithNiwsConfig()方法。在改方法中,经过一系列的初始化配置,最终执行了restOfInit()方法。其代码如下:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
public DynamicServerListLoadBalancer(IClientConfig clientConfig) {
initWithNiwsConfig(clientConfig);
}
@Override
public void initWithNiwsConfig(IClientConfig clientConfig) {
try {
super.initWithNiwsConfig(clientConfig);
String niwsServerListClassName = clientConfig.getPropertyAsString(
CommonClientConfigKey.NIWSServerListClassName,
DefaultClientConfigImpl.DEFAULT_SEVER_LIST_CLASS);
ServerList<T> niwsServerListImpl = (ServerList<T>) ClientFactory
.instantiateInstanceWithClientConfig(niwsServerListClassName, clientConfig);
this.serverListImpl = niwsServerListImpl;
if (niwsServerListImpl instanceof AbstractServerList) {
AbstractServerListFilter<T> niwsFilter = ((AbstractServerList) niwsServerListImpl)
.getFilterImpl(clientConfig);
niwsFilter.setLoadBalancerStats(getLoadBalancerStats());
this.filter = niwsFilter;
}
String serverListUpdaterClassName = clientConfig.getPropertyAsString(
CommonClientConfigKey.ServerListUpdaterClassName,
DefaultClientConfigImpl.DEFAULT_SERVER_LIST_UPDATER_CLASS
);
this.serverListUpdater = (ServerListUpdater) ClientFactory
.instantiateInstanceWithClientConfig(serverListUpdaterClassName, clientConfig);
restOfInit(clientConfig);
} catch (Exception e) {
throw new RuntimeException(
"Exception while initializing NIWSDiscoveryLoadBalancer:"
+ clientConfig.getClientName()
+ ", niwsClientConfig:" + clientConfig, e);
}
}

在restOfInit()方法上,有一个 updateListOfServers()的方法,该方法是用来获取所有的ServerList的。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
void restOfInit(IClientConfig clientConfig) {
boolean primeConnection = this.isEnablePrimingConnections();
// turn this off to avoid duplicated asynchronous priming done in BaseLoadBalancer.setServerList()
this.setEnablePrimingConnections(false);
enableAndInitLearnNewServersFeature();
updateListOfServers();
if (primeConnection && this.getPrimeConnections() != null) {
this.getPrimeConnections()
.primeConnections(getReachableServers());
}
this.setEnablePrimingConnections(primeConnection);
LOGGER.info("DynamicServerListLoadBalancer for client {} initialized: {}", clientConfig.getClientName(), this.toString());
}

进一步跟踪updateListOfServers()方法的源码,最终由serverListImpl.getUpdatedListOfServers()获取所有的服务列表的,代码如下:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
@VisibleForTesting
public void updateListOfServers() {
List<T> servers = new ArrayList<T>();
if (serverListImpl != null) {
servers = serverListImpl.getUpdatedListOfServers();
LOGGER.debug("List of Servers for {} obtained from Discovery client: {}",
getIdentifier(), servers);
if (filter != null) {
servers = filter.getFilteredListOfServers(servers);
LOGGER.debug("Filtered List of Servers for {} obtained from Discovery client: {}",
getIdentifier(), servers);
}
}
updateAllServerList(servers);
}

而serverListImpl是ServerList接口的具体实现类。跟踪代码,ServerList的实现类为DiscoveryEnabledNIWSServerList,在ribbon-eureka.jar的com.netflix.niws.loadbalancer下。其中DiscoveryEnabledNIWSServerList有 getInitialListOfServers()和getUpdatedListOfServers()方法,具体代码如下:

1
2
3
4
5
6
7
8
9
@Override
public List<DiscoveryEnabledServer> getInitialListOfServers(){
return obtainServersViaDiscovery();
}
@Override
public List<DiscoveryEnabledServer> getUpdatedListOfServers(){
return obtainServersViaDiscovery();
}

继续跟踪源码,obtainServersViaDiscovery(),是根据eurekaClientProvider.get()来回去EurekaClient,再根据EurekaClient来获取注册列表信息,代码如下:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
private List<DiscoveryEnabledServer> obtainServersViaDiscovery() {
List<DiscoveryEnabledServer> serverList = new ArrayList<DiscoveryEnabledServer>();
if (eurekaClientProvider == null || eurekaClientProvider.get() == null) {
logger.warn("EurekaClient has not been initialized yet, returning an empty list");
return new ArrayList<DiscoveryEnabledServer>();
}
EurekaClient eurekaClient = eurekaClientProvider.get();
if (vipAddresses!=null){
for (String vipAddress : vipAddresses.split(",")) {
// if targetRegion is null, it will be interpreted as the same region of client
List<InstanceInfo> listOfInstanceInfo = eurekaClient.getInstancesByVipAddress(vipAddress, isSecure, targetRegion);
for (InstanceInfo ii : listOfInstanceInfo) {
if (ii.getStatus().equals(InstanceStatus.UP)) {
if(shouldUseOverridePort){
if(logger.isDebugEnabled()){
logger.debug("Overriding port on client name: " + clientName + " to " + overridePort);
}
// copy is necessary since the InstanceInfo builder just uses the original reference,
// and we don't want to corrupt the global eureka copy of the object which may be
// used by other clients in our system
InstanceInfo copy = new InstanceInfo(ii);
if(isSecure){
ii = new InstanceInfo.Builder(copy).setSecurePort(overridePort).build();
}else{
ii = new InstanceInfo.Builder(copy).setPort(overridePort).build();
}
}
DiscoveryEnabledServer des = new DiscoveryEnabledServer(ii, isSecure, shouldUseIpAddr);
des.setZone(DiscoveryClient.getZone(ii));
serverList.add(des);
}
}
if (serverList.size()>0 && prioritizeVipAddressBasedServers){
break; // if the current vipAddress has servers, we dont use subsequent vipAddress based servers
}
}
}
return serverList;
}

其中eurekaClientProvider的实现类是LegacyEurekaClientProvider,它是一个获取eurekaClient类,通过静态的方法去获取eurekaClient,其代码如下:

1
2
3
4
5
6
7
8
9
10
11
12
13
class LegacyEurekaClientProvider implements Provider<EurekaClient> {
private volatile EurekaClient eurekaClient;
@Override
public synchronized EurekaClient get() {
if (eurekaClient == null) {
eurekaClient = DiscoveryManager.getInstance().getDiscoveryClient();
}
return eurekaClient;
}
}

EurekaClient的实现类为DiscoveryClient,在之前已经分析了它具有服务注册、获取服务注册列表等的全部功能。

由此可见,负载均衡器是从EurekaClient获取服务信息,并根据IRule去路由,并且根据IPing去判断服务的可用性。

那么现在还有个问题,负载均衡器多久一次去获取一次从Eureka Client获取注册信息呢。

在BaseLoadBalancer类下,BaseLoadBalancer的构造函数,该构造函数开启了一个PingTask任务,代码如下:

1
2
3
4
5
6
public BaseLoadBalancer(String name, IRule rule, LoadBalancerStats stats,
IPing ping, IPingStrategy pingStrategy) {
...//代码省略
setupPingTask();
...//代码省略
}

setupPingTask()的具体代码逻辑,它开启了ShutdownEnabledTimer执行PingTask任务,在默认情况下pingIntervalSeconds为10,即每10秒钟,想EurekaClient发送一次”ping”。

1
2
3
4
5
6
7
8
9
10
11
12
void setupPingTask() {
if (canSkipPing()) {
return;
}
if (lbTimer != null) {
lbTimer.cancel();
}
lbTimer = new ShutdownEnabledTimer("NFLoadBalancer-PingTimer-" + name,
true);
lbTimer.schedule(new PingTask(), 0, pingIntervalSeconds * 1000);
forceQuickPing();
}

PingTask源码,即new一个Pinger对象,并执行runPinger()方法。

1
2
3
4
5
6
7
8
9
class PingTask extends TimerTask {
public void run() {
try {
new Pinger(pingStrategy).runPinger();
} catch (Exception e) {
logger.error("LoadBalancer [{}]: Error pinging", name, e);
}
}
}

查看Pinger的runPinger()方法,最终根据 pingerStrategy.pingServers(ping, allServers)来获取服务的可用性,如果该返回结果,如之前相同,则不去向EurekaClient获取注册列表,如果不同则通知ServerStatusChangeListener或者changeListeners发生了改变,进行更新或者重新拉取。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
public void runPinger() throws Exception {
if (!pingInProgress.compareAndSet(false, true)) {
return; // Ping in progress - nothing to do
}
// we are "in" - we get to Ping
Server[] allServers = null;
boolean[] results = null;
Lock allLock = null;
Lock upLock = null;
try {
/*
* The readLock should be free unless an addServer operation is
* going on...
*/
allLock = allServerLock.readLock();
allLock.lock();
allServers = allServerList.toArray(new Server[allServerList.size()]);
allLock.unlock();
int numCandidates = allServers.length;
results = pingerStrategy.pingServers(ping, allServers);
final List<Server> newUpList = new ArrayList<Server>();
final List<Server> changedServers = new ArrayList<Server>();
for (int i = 0; i < numCandidates; i++) {
boolean isAlive = results[i];
Server svr = allServers[i];
boolean oldIsAlive = svr.isAlive();
svr.setAlive(isAlive);
if (oldIsAlive != isAlive) {
changedServers.add(svr);
logger.debug("LoadBalancer [{}]: Server [{}] status changed to {}",
name, svr.getId(), (isAlive ? "ALIVE" : "DEAD"));
}
if (isAlive) {
newUpList.add(svr);
}
}
upLock = upServerLock.writeLock();
upLock.lock();
upServerList = newUpList;
upLock.unlock();
notifyServerStatusChangeListener(changedServers);
} finally {
pingInProgress.set(false);
}
}

由此可见,LoadBalancerClient是在初始化的时候,会向Eureka回去服务注册列表,并且向通过10s一次向EurekaClient发送“ping”,来判断服务的可用性,如果服务的可用性发生了改变或者服务数量和之前的不一致,则更新或者重新拉取。LoadBalancerClient有了这些服务注册列表,就可以根据具体的IRule来进行负载均衡。

RestTemplate是如何和Ribbon结合的

最后,回答问题的本质,为什么在RestTemplate加一个@LoadBalance注解就可可以开启负载均衡呢?

1
2
3
4
@LoadBalanced
RestTemplate restTemplate() {
return new RestTemplate();
}

全局搜索ctr+shift+f @LoadBalanced有哪些类用到了LoadBalanced有哪些类用到了, 发现LoadBalancerAutoConfiguration类,即LoadBalancer自动配置类。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
@Configuration
@ConditionalOnClass(RestTemplate.class)
@ConditionalOnBean(LoadBalancerClient.class)
@EnableConfigurationProperties(LoadBalancerRetryProperties.class)
public class LoadBalancerAutoConfiguration {
@LoadBalanced
@Autowired(required = false)
private List<RestTemplate> restTemplates = Collections.emptyList();
}
@Bean
public SmartInitializingSingleton loadBalancedRestTemplateInitializer(
final List<RestTemplateCustomizer> customizers) {
return new SmartInitializingSingleton() {
@Override
public void afterSingletonsInstantiated() {
for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {
for (RestTemplateCustomizer customizer : customizers) {
customizer.customize(restTemplate);
}
}
}
};
}
@Configuration
@ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
static class LoadBalancerInterceptorConfig {
@Bean
public LoadBalancerInterceptor ribbonInterceptor(
LoadBalancerClient loadBalancerClient,
LoadBalancerRequestFactory requestFactory) {
return new LoadBalancerInterceptor(loadBalancerClient, requestFactory);
}
@Bean
@ConditionalOnMissingBean
public RestTemplateCustomizer restTemplateCustomizer(
final LoadBalancerInterceptor loadBalancerInterceptor) {
return new RestTemplateCustomizer() {
@Override
public void customize(RestTemplate restTemplate) {
List<ClientHttpRequestInterceptor> list = new ArrayList<>(
restTemplate.getInterceptors());
list.add(loadBalancerInterceptor);
restTemplate.setInterceptors(list);
}
};
}
}
}

在该类中,首先维护了一个被@LoadBalanced修饰的RestTemplate对象的List,在初始化的过程中,通过调用customizer.customize(restTemplate)方法来给RestTemplate增加拦截器LoadBalancerInterceptor。

而LoadBalancerInterceptor,用于实时拦截,在LoadBalancerInterceptor这里实现来负载均衡。LoadBalancerInterceptor的拦截方法如下:

1
2
3
4
5
6
7
8
@Override
public ClientHttpResponse intercept(final HttpRequest request, final byte[] body,
final ClientHttpRequestExecution execution) throws IOException {
final URI originalUri = request.getURI();
String serviceName = originalUri.getHost();
Assert.state(serviceName != null, "Request URI does not contain a valid hostname: " + originalUri);
return this.loadBalancer.execute(serviceName, requestFactory.createRequest(request, body, execution));
}

总结

综上所述,Ribbon的负载均衡,主要通过LoadBalancerClient来实现的,而LoadBalancerClient具体交给了ILoadBalancer来处理,ILoadBalancer通过配置IRule、IPing等信息,并向EurekaClient获取注册列表的信息,并默认10秒一次向EurekaClient发送“ping”,进而检查是否更新服务列表,最后,得到注册列表后,ILoadBalancer根据IRule的策略进行负载均衡。

而RestTemplate 被@LoadBalance注解后,能过用负载均衡,主要是维护了一个被@LoadBalance注解的RestTemplate列表,并给列表中的RestTemplate添加拦截器,进而交给负载均衡器去处理。

转载请标明出处:
http://blog.csdn.net/forezp/article/details/74820899
本文出自方志朋的博客