Rate Limiting for Streaming APIs

Overview

All WSO2 API Manager Streaming APIs (namely WebSocket APIs, WebHook APIs, WebSub APIs, and SSE APIs) use the following rate limiting policies in subscriptions by way of Business Plans. You can use any of the following rate limiting policies when working with monetization.

  • Count-based Rate Limiting Policy - Rate limiting policies based on the number of total events an application can receive. For example, 1M total events, 10M events or Unlimited events. After the application reaches its limit the API Gateway will throttle out the application.

  • Time-based Rate Limiting Policy - Rate limiting policies based on how long the client can subscribe to a given topic/API. For example, 1 week, 1 month or forever. After the client reaches the specified time limit, the API Gateway will throttle out the client.

  • Count-time Hybrid Rate Limiting Policy - This refers to rate limiting policies that are based on both the above-mentioned "Time-based Rate Limiting policy" and the "Count-based Rate Limiting policy." For example, 1M events within a day.

How it works

WSO2 API Manager supports Streaming APIs that are based on the WebSocket, Server-Sent Events (SSE), and WebSub (also known as WebHook) protocols. The following sections describe the way in which WSO2 API Manager handles rate limiting for each of the Streaming APIs.

WebSockets

Once the initial handshake is done, the communication in a WebSocket connection is done via WebSocket frames. WebSocket frames can be sent from client to server, and vice versa. Each WebSocket frame is counted as an event. WebSocket frames will be throttled out once the aggregate amount of frames sent from client to server and vice versa reach the amount defined in the rate limiting policy.

Server-Sent Events (SSE)

In Server Sent Events, every event is counted. An event is usually delimited with \n\n. The connection will be throttled out when the number of events from the server to the client reaches the amount defined in the rate limiting policy.

WebSub (WebHook)

Rate limiting events are counted in the following ways for WebSub Streaming APIs (WebHook Streaming APIs).

  • Number of Active Connections

    The number of active connections, for an application subscription, in a given time unit.

  • Number of Events

    The number of events, which can be consumed for a given unit of time, for a single application subscription.

A throttled out message will be sent to the callback URL, upon receiving the very first message after being throttled out.

Business Plans

The API Creators need to select a minimum of one Business Plan when creating a Streaming API. These Business Plans can be either a default Business Plan, a Custom Business Plan, or a hybrid of Default and Custom Business Plans. The Business Plans are used to enforce rate limiting by allowing you to limit the number of events via the Streaming API during a given period of time.

Default Business Plans

Streaming API Business Plans

The following is the list of default Business Plans that are related to Streaming APIs.

Default Business Plans Applicable API
AsyncGold : Allows 50000 events per day WebSocket, SSE
AsyncSilver : Allows 25000 events per day WebSocket, SSE
AsyncBronze : Allows 5000 events per day WebSocket, SSE
AsyncUnlimited : Allows unlimited events WebSocket, SSE
AsyncWHGold : Allows 10000 events per month and 1000 active subscriptions WebHook/WebSub
AsyncWHSilver : Allows 5000 events per month and 500 active subscriptions WebHook/WebSub
AsyncWHBronze : Allows 1000 events per month and 500 active subscriptions WebHook/WebSub

Custom Business Plans

Instead of using the default Business Plans, a user who has the admin role, with access to the Admin Portal, can create Custom Business Plans, which API Creators can use. For more information, see Adding a new subscription-level throttling tier.

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