Azure Functions Proxies Preview

Azure functions allow the creation of HTTP-triggered code. A new feature to Functions is the ability to define proxies. (Note: at the time of writing this feature is in preview)

For example a function can be created that responds to HTTP GETs to retrieve a customer as the following code demonstrates:

using System.Net;

public class Customer 
{
    public int Id {get; set;}    
    public string Name {get; set;}
}

public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, TraceWriter log)
{
    // error checking omitted

    string id = req.GetQueryNameValuePairs()
        .FirstOrDefault(q => string.Compare(q.Key, "id", true) == 0)
        .Value;

    return req.CreateResponse(HttpStatusCode.OK, GetById(int.Parse(id)));
}

public static Customer GetById(int id)
{
    // simulate fetching a customer, e.g. from Table storage, db, etc.
    return new Customer
        {
            Id = id,
            Name = "Amrit"
        };
}

This function (called “GetCustomer”) could be available at the following URL (with function authorization enabled): https://dontcodetireddemos.azurewebsites.net/api/GetCustomer?id=42&code=rEQKsObGFDRCCiVuLhOnZ1Rdfn/XGgp5tfC1xHrhAqxvWqzHSQszCg==

Notice in the URL the name of the function is prefixed with “api” i.e. “api/GetCustomer”

Calling this URL would result in the following JSON being returned:

{
  "Id": 42,
  "Name": "Amrit"
}

Function proxies allow the “api” part to be replaced, for example to create a URL:  “https://dontcodetireddemos.azurewebsites.net/customer?id=42&code=rEQKsObGFDRCCiVuLhOnZ1Rdfn/XGgp5tfC1xHrhAqxvWqzHSQszCg==”

This proxy defines a name “CustomerGet”, a route template of “customer”, the actual URL to maps to “https://dontcodetireddemos.azurewebsites.net/api/GetCustomer”, and limited to only GET HTTP verbs.

If we had another function e.g. called PostCustomer we could also setup a POST proxy for that function:

Now we can issue both POSTs and GETs to the customer “resource” at: https://dontcodetireddemos.azurewebsites.net/customer (code key omitted).

Using Kudu for example, we can see a proxies.js file created in the wwwroot folder with the following contents:

{
    "proxies": {
        "CustomerGet": {
            "matchCondition": {
                "route": "customer",
                "methods": [
                    "GET"
                ]
            },
            "backendUri": "https://dontcodetireddemos.azurewebsites.net/api/GetCustomer"
        },
        "CustomerPost": {
            "matchCondition": {
                "route": "customer",
                "methods": [
                    "POST"
                ]
            },
            "backendUri": "https://dontcodetireddemos.azurewebsites.net/api/PostCustomer"
        }
    }
}