Azure API Management with Call Chain of Backend APIs

The backend can be rest api or soap api.

The call scenario:

We can integrate APIs to Azure API Management services and  implement policies in API Manager to achieve this goal.  Please refer to Policies

Step 1

First, we need to identify what APIs are required to aggregate and their input parameters. In my case, I had two APIs; one gives profile details and the other one fetches the user tasks of that user. 

1. http://companywebapp.azurewebsites.net/api/Profile?id={accountId}  
2. http://companyebapp.azurewebsites.net/api/Task?id={accountId}  

The common input parameter for both APIs is accountId.

Step 2

Create a new operation with name Dashboard as Get request with query parameter accountId and save. 

Step 3

Open the policy editor for Dashboard operation by clicking Inbound Processing-->Code view.

We need to create a variable with name accountId like below. We can use this variable to pass the value into the APIs.

1. <set-variable name="accountId" value="@(context.Request.Url.Query["accountId"].Last())" />  

Step 4

Create a send-request policy for API1 and API2 which fetches profile details and profile tasks. The response-variable-name stores the response from the API. On set-url, we use the API to hit, which we want to fetch data from and stores the response to response-variable-name we declared. In set-method, we specify the HttpVerb based on the request we made. If we want to pass any values in the header we pass in set-header value.

<send-request mode="new" response-variable-name="profiledetails" timeout="20" ignore-error="true">  

            <set-url>@($"http://companywebapp.azurewebsites.net/api/Profile?id={(string)context.Variables["accountId"]}")</set-url>  

            <set-method>GET</set-method>  

            <set-header name="Content-Type" exists-action="override">  

                <value>application/x-www-form-urlencoded</value>  

            </set-header>>  

        </send-request>  

<send-request mode="new" response-variable-name="taskdetails" timeout="20" ignore-error="true">  

            <set-url>@($"http://companywebapp.azurewebsites.net/api/Task?id={(string)context.Variables["accountId"]}")</set-url>  

            <set-method>GET</set-method>  

            <set-header name="Content-Type" exists-action="override">  

                <value>application/x-www-form-urlencoded</value>  

            </set-header>  

        </send-request>  

Step 5

We need to collect the response from the two APIs and use return-response policy to send the data. In return-reponse policy we need to aggregate the responses in set-body policy. In the previous step we collected the response and stored in profiledetails and taskdetails.

This part is the final response, on set-body we are casting the response to JSON object and aggregating the two API response.

<return-response>  

            <set-status code="200" reason="OK" />  

            <set-header name="Content-Type" exists-action="override">  

                <value>application/json</value>  

            </set-header>  

            <set-body>@(new JObject(new JProperty("profiledetails",((IResponse)context.Variables["profiledetails"]).Body.As<JObject>()),  

                            new JProperty("taskdetails",((IResponse)context.Variables["taskdetails"]).Body.As<JObject>())  

                            ).ToString())</set-body>  

        </return-response>  

Summary

By following these simple steps, we can aggregate two API's responses and send a single collective response. The example is very simple but in a real-time scenario, you may encounter multiple APIs with a lot of input parameters.