Using the Virtual Endpoint middleware with Tyk OAS APIs

The virtual endpoint middleware provides a serverless compute function that allows for the execution of custom logic directly within the gateway itself, without the need to proxy the request to an upstream service. This functionality is particularly useful for a variety of use cases, including request transformation, aggregation of responses from multiple services, or implementing custom authentication mechanisms.

The middleware is configured in the Tyk OAS API Definition. You can do this via the Tyk Dashboard API or in the API Designer.

If you’re using the legacy Tyk Classic APIs, then check out the Tyk Classic page.

Configuring the middleware in the Tyk OAS API Definition

The design of the Tyk OAS API Definition takes advantage of the operationId defined in the OpenAPI Document that declares both the path and method for which the middleware should be added. Endpoint paths entries (and the associated operationId) can contain wildcards in the form of any string bracketed by curly braces, for example /status/{code}. These wildcards are so they are human readable and do not translate to variable names. Under the hood, a wildcard translates to the “match everything” regex of: (.*).

The virtual endpoint middleware (virtualEndpoint) can be added to the operations section of the Tyk OAS Extension (x-tyk-api-gateway) in your Tyk OAS API Definition for the appropriate operationId (as configured in the paths section of your OpenAPI Document).

The virtualEndpoint object has the following configuration:

• enabled: enable the middleware for the endpoint
• functionName: the name of the JavaScript function that will be executed when the virtual endpoint is triggered
• body: [optional] a base64 encoded string containing the JavaScript code
• path: [optional] the relative path to the source file containing the JavaScript code
• proxyOnError: [optional, defaults to false] a boolean that determines the behavior of the gateway if an error occurs during the execution of the virtual endpoint’s function; if set to true the request will be proxied to upstream if the function errors, if set to false the request will not be proxied and Tyk will return an error response
• requireSession: [optional defaults to false] a boolean that indicates whether the virtual endpoint should have access to the session object; if true then the key session data will be provided to the function as the session variable

For example:

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{
    "components": {},
    "info": {
        "title": "example-virtual-endpoint",
        "version": "1.0.0"
    },
    "openapi": "3.0.3",
    "paths": {
        "/anything": {
            "get": {
                "operationId": "anythingget",
                "responses": {
                    "200": {
                        "description": ""
                    }
                }
            }
        }
    },
    "x-tyk-api-gateway": {
        "info": {
            "name": "example-virtual-endpoint",
            "state": {
                "active": true,
                "internal": false
            }
        },
        "upstream": {
            "url": "http://httpbin.org/"
        },          
        "server": {
            "listenPath": {
                "value": "/example-virtual-endpoint/",                
                "strip": true
            }
        },      
        "middleware": {
            "global": {
                "pluginConfig": {
                    "data": {
                        "enabled": true,
                        "value": {
                            "map": {
                                "key": 3
                            },
                        "num": 4,
                        "string": "example"
                        }
                    }
                }
            },
            "operations": {
                "anythingget": {
                    "virtualEndpoint": {
                        "enabled": true,
                        "functionName": "myVirtualHandler",
                        "body": "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"
                    }
                }
            }
        }
    }
}

In this example the virtual endpoint middleware has been configured for requests to the GET /anything endpoint. We have also configured the following custom attributes in the pluginConfig section of the API definition:

{
    "map": {
        "key": 3
    },
    "num": 4,
    "string": "example"
}

The body field value is a base64 encoded string containing this JavaScript code, which will be invoked by the virtual endpoint middleware:

function myVirtualHandler (request, session, config) {      
  var responseObject = {
    Body: "Virtual Endpoint "+config.config_data.string,
    Headers: {
      "foo-header": "bar",
      "map-header": JSON.stringify(config.config_data.map),
      "string-header": config.config_data.string,
      "num-header": JSON.stringify(config.config_data.num)
    },
    Code: 200
  }
  return TykJsResponse(responseObject, session.meta_data)
}

A call to the GET /anything endpoint returns:

HTTP/1.1 200 OK
Date: Fri, 01 Mar 2024 12:14:36 GMT
Foo-Header: bar
Map-Header: {"key":3}
Num-Header: 4
Server: tyk
String-Header: example
Content-Length: 24
Content-Type: text/plain; charset=utf-8
 
Virtual Endpoint example

The configuration above is a complete and valid Tyk OAS API Definition that you can import into Tyk to try out the virtual endpoint middleware.

Configuring the middleware in the API Designer

Adding a Virtual Endpoint to your API endpoints is easy when using the API Designer in the Tyk Dashboard, simply follow these steps:

Step 1: Add an endpoint

From the API Designer add an endpoint that matches the path and method to which you want to apply the middleware.

Step 2: Select the Virtual Endpoint middleware

Select ADD MIDDLEWARE and choose Virtual Endpoint from the Add Middleware screen.

Step 3: Configure the middleware

Now you can provide either the path to a file containing the JavaScript function to be run by the middleare, or you can directly enter the JavaScript in the code editor.

For both sources, you must provide the function name that should be called when the middleware executes.

You can also optionally configure the behavior required if the function should return an error and also indicate to Tyk whether the virtual middleware requires access to the key session metadata.

Step 4: Save the API

Select ADD MIDDLEWARE to save the middleware configuration. Remember to select SAVE API to apply the changes.