如何：控制并发和限流

只允许通知执行给定数量的请求时分布式计算中一个常见的场景 使用Dapr，你可以控制同时有多少个应用和时间可以调用你的应用

请注意，这个速率限制对每一个来自Dapr的事件都是有保证的，这意味着Pub/Sub事件、来自其他服务的直接调用、绑定事件等等。 Dapr不能对从从Dapr外部调用你的应用程序的请求应用并发策略。

*Note that rate limiting per second can be achieved by using the middleware.http.ratelimit middleware. However, there is an imporant difference between the two approaches. The rate limit middlware is time bound and limits the number of requests per second, while the app-max-concurrency flag specifies the number of concurrent requests (and events) at any point of time. See Rate limit middleware. * However, there is an imporant difference between the two approaches. The rate limit middlware is time bound and limits the number of requests per second, while the app-max-concurrency flag specifies the number of concurrent requests (and events) at any point of time. See Rate limit middleware. *

Watch this video on how to control concurrency and rate limiting “.

设置 app-max-concurrency

如果不适用Dapr，开发者需要在应用中创建某种信号量，并且负责获取和释放它 使用 Dapr，应用程序不需要代码更改。

在Kubernetes中设置app-max-concurrency

To set app-max-concurrency in Kubernetes, add the following annotation to your pod:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nodesubscriber
  namespace: default
  labels:
    app: nodesubscriber
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nodesubscriber
  template:
    metadata:
      labels:
        app: nodesubscriber
      annotations:
        dapr.io/enabled: "true"
        dapr.io/app-id: "nodesubscriber"
        dapr.io/app-port: "3000"
        <b>dapr.io/app-max-concurrency: "1"</b>
...

Setting app-max-concurrency using the Dapr CLI

To set app-max-concurrency with the Dapr CLI for running on your local dev machine, add the app-max-concurrency flag:

dapr run --app-max-concurrency 1 --app-port 5000 python ./app.py

The above examples will effectively turn your app into a single concurrent service.