Set up an API within Azure API Management to facilitate the implementation of server-sent events.

Server-Sent Events (SSE) is a web technology designed to enable servers to transmit data to clients without the need for client-initiated requests. SSE proves to be highly advantageous for applications requiring real-time updates, such as chat platforms, news feeds, or stock price trackers. Traditionally, these applications would involve clients repeatedly requesting data from servers at predefined intervals.

This blog post delves into the configuration process of setting up a server-sent events (SSE) API within Azure API Management (APIM). APIM is a comprehensive service offering the creation, publication, management, and security of APIs. APIM facilitates SSE APIs by applying a specialized policy that enables the seamless transmission of streaming responses.

Step-by-Step Guide: Configuring a Sample SSE API in Azure API Management

To configure a sample SSE API in APIM, adhere to the following instructions:

• Let's consider the following publicly accessible SSE API provided by Postman as an illustrative example:

   postman-echo.com/server-events/:numberOfEvents

• Import this SSE API as a HTTP API into APIM, depending on your specific requirements,

• Create a GET operation that includes a query parameter named 'eventscount' to specify the desired number of events to generate,

• Navigate to the Inbound processing tab and incorporate the "Stream response content" policy as demonstrated below. 

• Save the policy and proceed to test the SSE API within APIM.

Testing:

• Fetch the Request URL of the API endpoint from Azure Portal:

• Utilize Postman or any other SSE-compatible tool to send a GET request to the APIM endpoint, including the query parameter ‘eventscount’ with a value of, for example, 10.

• You should observe the streaming of 10 events with data being transmitted from the server and we can confirm that the APIM endpoint successfully streams the events retrieved from the backend server.

Potential causes for the SSE API not functioning as anticipated in APIM may include:

When utilizing APIM to access a backend API implementing SSE, it is essential to follow these guidelines for verification:

• To prevent issues with SSE APIs in APIM, it is recommended to disable request/response body logging for Azure Monitor and Application Insights. These services offer application performance monitoring features, allowing the logging of request/response bodies at various stages of request execution. However, for SSE APIs, logging can cause unexpected buffering and potential problems. Azure Monitor and Application Insights diagnostic settings configured at the global/All APIs scope apply to all APIs within the service, but you can override these settings for individual APIs as needed. Disabling request/response body logging ensures improved performance and reliability of SSE APIs by avoiding unnecessary data collection.

• SSE requires a persistent HTTP connection, which is supported by the dedicated API Management tiers (Premium, Standard, Basic, and Developer). However, the Consumption tier does not support persistent connections. Consider selecting a suitable service tier that supports SSE based on your requirements.
• To prevent idle connections from timing out, it is recommended to use methods that keep them active. For example, you can set up a TCP keepalive signal on the backend side of the connection or ensure that the client sends data at least every 4 minutes.
• To ensure clients receive events as soon as they occur, disable response buffering in the forward-request policy. This can be achieved by setting the buffer-response attribute to false, as demonstrated below:

• Avoid using policies that introduce delays in responses. Certain policies like validate-content can hold up response content, which is not suitable for SSE APIs.
• Make sure to disable response caching to ensure that clients receive timely notifications.
• Before launching your API, thoroughly test its performance under stress. Utilize common methods to simulate heavy load and identify any speed or stability issues.

I hope you find these guidelines helpful and informative. If you have any questions or feedback, please feel free to leave a comment below :)

Reference: https://learn.microsoft.com/en-us/azure/api-management/how-to-server-sent-events