Month: April 2018

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Using Azure APIM Policies to Route on HTTP Verbs & Resources

The policies available in APIM are indeed very powerful. It provides the ability to modify the backend flow of a request using rules based on the payload contents or the request context properties. I have yet to find a scenario where I could not resolve a requirement using the inbuilt statements.

One example is I had to send a request to different endpoints depending on the request verb (Post,Put,Delete) and the resource location.

image

A policy inspects the incoming request Url and the operation method to determine which Azure Logic App or Function to forward the request onto.

The inbound policy section for this scenario is shown below. It uses the Xslt Choose function to match on the Url path and the operation. If a match is found, it sets the variable “logicappEndpoint” to the name-value variable defined in the Azure APIM blade.

<inbound>

    <choose>

        <when condition="@(context.Request.Url.Path.Equals("inventory")  && context.Operation.Method.Equals("PUT"))">

            <set-variable name="logicappEndpoint" value="{{UAT-AXProductUpdateUrl}}" />

        </when>

        <when condition="@(context.Request.Url.Path.Equals("inventory")  && context.Operation.Method.Equals("POST"))">

            <set-variable name="logicappEndpoint" value="{{UAT-AXProductCreateUrl}}" />

        </when>

        <when condition="@(context.Request.Url.Path.Equals("inventory") && context.Operation.Method.Equals("DELETE"))">

            <set-variable name="logicappEndpoint" value="{{UAT-AXProductDeleteUrl}}" />

        </when>

        <when condition="@(context.Request.Url.Path.Equals("stockmovement") && context.Operation.Method.Equals("PUT"))">

            <set-variable name="logicappEndpoint" value="{{UAT-AXStockMovementUpdateUrl}}" />

        </when>

        <when condition="@(context.Request.Url.Path.Equals("stockmovement") && context.Operation.Method.Equals("POST"))">

            <set-variable name="logicappEndpoint" value="{{UAT-AXStockMovementCreateUrl}}" />

        </when>        

    </choose>

    <base />

</inbound>

To reference the Named-Value properties defined in the portal from within a policy, simply wrap the property name with double braces as shown here as an example:-  {{UAT-AXStockMovementCreateUrl}}

These Name-Values pairs are then created in APIM blade of the Azure Portal shown below.

image

Once the Inbound policy section has been created, we then need to create the rule for the Backend section shown below. Here I am also setting a retry condition to 3 times before sending back a status error code of 500.  Also I am always forwarding the request to the Logic App as a POST.

<backend>

    <retry condition="@(context.Response.StatusCode == 500)" count="3" interval="5" max-interval="10" delta="2" first-fast-retry="false">

        <send-request mode="copy" response-variable-name="tokenstate" timeout="120" ignore-error="true">

            <set-url>@(context.Variables.GetValueOrDefault<string>("logicappEndpoint"))</set-url>

            <set-method>POST</set-method>

            <set-header name="Ocp-Apim-Subscription-Key" exists-action="delete" />

        </send-request>

    </retry>

</backend>

 

I hope this short blog gives you a basic understanding of how to redirect a request based on the HTTP verb and a resource location. Enjoy…