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. http://companywebapp.azurewebsites.net/api/Profile?id={accountId} 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. <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.
