Server-Sent Events (SSE) is a server push technology enabling a subscribed client to receive automatic updates from a server via a long running HTTP connection. Unlike WebSockets, SSE is a one-way communication of server to clients (WebSockets is a bidirectional communication between server and client). As such, if you only need clients to receive data from a server, and don’t require them sending messagess back, SSE could be a simpler way to make that happen. An online stock quotes, or notifications and feeds are good examples for applications that use SSE.

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Using Tyk as a server-sent events (SSE) Proxy

Tyk Gateway supports SSE proxying over HTTP, and can sit in the middle between the client and the SSE server and support the server sending updates to the client.

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Setup

  • Enable SSE support on the Gateway: Set http_server_options.enable_websockets to true in your Tyk Gateway config file.
  • To maintain an open connection between the API consumer and the Tyk Gateway, set http_server_options.read_timeout and http_server_options.write_timeout to appropriately high values (in milliseconds). For example, you could try setting both to 2000, but this is for you to determine in your environment.
  • Set http_server_options.flush_interval to an appropriate value, e.g. 1, to force Tyk to stream the response to the client every n seconds.

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Example using Tyk as an SSE proxy

For this we will need:
  • An SSE server. For this example we will use Golang HTML 5 SSE example
  • An instance of the Tyk Gateway and optionally the Tyk Dashboard
Steps for Configuration:
  • Ensure the Gateway configurations detailed in the Setup section are set.
  • Run the SSE server as per the example instructions. By default this runs on port 8000.
go run ./server.go
  • Publish an API with the following configuration:
    1. Set an appropriate listen path, e.g. "listen_path": "/sse"
    2. Strip the listen path, e.g. "strip_listen_path": true,
    3. Set the target url as the SSE server, e.g. the example SSE server:"target_url": "http://host.docker.internal:8000"
    4. Click Save, and wait for the Gateway to reload the API before testing it
  • To test the protected SSE service via the API in the Tyk Gateway run:
curl http://localhost:8080/sse/events/
You should see a stream of updates from the server. In this example, you will see: 
Message: 20 - the time is 2013-03-08 21:08:01.260967 -0500 EST
Message: 21 - the time is 2013-03-08 21:08:06.262034 -0500 EST
Message: 22 - the time is 2013-03-08 21:08:11.262608 -0500 EST