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WebSocket support in API Gateway

The API Gateway includes a basic WebSocket proxy which enables the Gateway to access applications that use the WebSocket protocol together with a web UI and a REST API.

The service defines which WebSocket endpoints are exposed by using Eureka metadata.

Example:

eureka:
    instance:
        metadata-map:
            apiml:
                routes:
                    ws_v1:
                        gatewayUrl: "ws/v1"
                        serviceUrl: /${serviceId}/ws

These metadata make it possible for requests from wss://gatewayHost:gatewayPort/${serviceId}/ws/v1/path to map to wss://serviceHost:servicePort/${serviceId}/ws/v1/path.

Where:

  • serviceId
    is the service ID of the service.

  • path
    is the remaining path segment in the URL.

Architecture​

In WebSocket routing, the API ML Gateway acts as both a WebSocket server for the client requesting this connection, and as a WebSocket client.

The following schema describes the interactions between client-side and server-side components where the Gateway has a double role as both client and server.

Client (i.e. web browser) <-> [Gateway (WebSocket Server) - Gateway (WebSocket Client)] <-> Service's WebSocket Server

Tip: We recommend that clients implement a ping-like mechanism to maintain the opened WebSocket sessions and not rely on the web browser to perform this action.

Security and Authentication​

The API Gateway usually uses TLS with the wss protocol. Services that use TLS enable the API Gateway to use wss to access these services. Services that do not use TLS require the API Gateway to use the ws protocol without TLS. The API Gateway also supports basic authentication via WebSocket.

Subprotocols​

In addition to plain WebSocket support, API Mediation Layer also supports WebSocket subprotocols. Currently, only STOMP v1.2 and STOMP v1.1 are supported and tested.

Note: It is possible to update the list of currently supported WebSocket subprotocols. Update the API Gateway configuration using the environment variable SERVER_WEBSOCKET_SUPPORTEDPROTOCOLS with the value of comma-separated subprotocol names. Support for additional subprotocols is not guaranteed as these subprotocols are not being tested.

Example:

SERVER_WEBSOCKET_SUPPORTEDPROTOCOLS=v12.stomp,v11.stomp,wamp,soap

High availability​

In the high availability scenario, a WebSocket session is established between client and a selected Gateway. This session is then tied to this instance for its entire duration.

Idle Timeout​

The WebSocket client on the API ML Gateway has a default Idle timeout of one hour. If a WebSocket session between the Gateway WebSocket Client and the Service's WebSocket Server is inactive for the entire period, the connection is closed.

To customize this setting, set the following property in zowe.yaml:

gateway:
    server:
      webSocket:
        maxIdleTimeout: 300000

Note: This setting is global for the API ML Gateway.

Diagnostics​

The list of active routed WebSocket sessions is available at the Actuator endpoint websockets. On localhost, it is available at https://localhost:10010/application/websockets.

The actuator endpoint is enabled with debugging enabled in the API ML Gateway.

Limitations​

Different HTTP status code errors may result. The WebSocket session starts before the session starts between the Gateway and the service. When a failure occurs when connecting to a service, the WebSocket session terminates with the WebSocket close code and a description of the failure that occurred between the Gateway and the Service rather than an HTTP error code.

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