Sentinel（服务限流/降级/授权）

对当前访问资源限流

关联资源影响当前限流

只限制指定链路上的流量

直接抛异常

指定时间内只开放阈值的1/3

指定时间过去后阈值完全开放

调用失败时不会立马抛异常，而是排队等待

指定毫秒间隔后再次调用，再失败才抛异常

单个请求的响应时间超过阈值，则进入准降级状态，接下来 1 秒内连续&nbsp;5 个请求响应时间均<br>超过阈值，就进行降级，持续时间为时间窗口的值（sentinel 1.8 后支持自定义最小请求数）

时间窗口期过后，如果接下来的一个请求成功完成则结束熔断，否则会再次被熔断

每秒内请求数目大于设置的最小请求数目，并且异常的比例大于阈值，则降级，持续时间为时窗口的值

时间窗口期过后，如果接下来的一个请求成功完成则结束熔断，否则会再次被熔断

1 分钟内的异常数超过阈值就进行降级处理，时间窗口的值要大于 60秒，否则刚结束熔断又进入下次熔断

/**<br> * @SentinelResource: 指定资源名称，作用与 HystrixCommand 大体一致<br> * blockHandler: 指定降级处理方法，类似于 Hystrix的fallbackMethod 兜底方法<br> */<br> @GetMapping("/testHotKeyRule")<br> @SentinelResource(value = "testHotKeyRule", blockHandler = "testHotKeyRule_blockHandler")<br> public String testHotKeyRule(@RequestParam(value = "username", required = false) String username,<br>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;@RequestParam(value = "password", required = false) String password) {<br>&nbsp; &nbsp; &nbsp; &nbsp; return "[热点限流规则]testHotKeyRule..";<br> }<br><br> public String testHotKeyRule_blockHandler(@RequestParam(value = "username", required = false) String username,<br>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;@RequestParam(value = "password", required = false) String password,<br>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;BlockException exception) {<br>&nbsp; &nbsp; &nbsp; &nbsp; return "[热点限流规则-兜底方法]testHotKeyRule_blockHandler..";<br> }

public class CustomBlockHandler {<br>&nbsp; &nbsp; public static JsonResult customBlockHandlerMethodA(BlockException exception) {<br>&nbsp; &nbsp; &nbsp; &nbsp; return new JsonResult(500, "[客户自定义限流处理逻辑]---&gt;customBlockHandlerMethodA");<br>&nbsp; &nbsp; }<br>&nbsp; &nbsp; public static JsonResult customBlockHandlerMethodB(BlockException exception) {<br>&nbsp; &nbsp; &nbsp; &nbsp; return new JsonResult(500, "[客户自定义限流处理逻辑]---&gt;customBlockHandlerMethodB");<br>&nbsp; &nbsp; }<br>}

@GetMapping("/customBlockHandler")<br> @SentinelResource(value = "customBlockHandler",<br><b> blockHandlerClass = CustomBlockHandler.class,<br> blockHandler = "customBlockHandlerMethodA")<br></b> public JsonResult customerBlockHandler() {<br>&nbsp; &nbsp; return new JsonResult(200, "客户自定义限流处理逻辑", new Payment(20200906L, UUID.randomUUID().toString()));<br> }