Azure APIM Policy to failover primary backend URL to secondary in case of a status code 429

I have an APIM endpoint that calls a backend HTTP service. If it returns the status code 429, the call needs to be retried to the secondary backend. The backends are working fine without any issues. I tried setting this is retry policy as below but it didn't work.

My requirement is when the primary backend sends a status code of 429, the request should go to the secondary backend without any retry on primary backend. Can someone help me on this?

Below is the policy i used and Please find the trace logs for the same policy here


<policies>
    <inbound>
        <base />
        <set-method>GET</set-method>
        <rewrite-uri id="apim-generated-policy" template="/" />
        <set-header id="apim-generated-policy" name="Ocp-Apim-Subscription-Key" exists-action="delete" />
    </inbound>
    <backend>
        <retry condition="@(context.Response.StatusCode == 429)" count="1" interval="1" first-fast-retry="true">
            <choose>
                <when condition="@(context.Response.StatusCode == 429)">
                    <set-backend-service base-url="https://secondaryserver.eastus.azurecontainerapps.io/" />
                </when>
            </choose>
            <forward-request />
        </retry>
    </backend>
    <outbound>
        <base />
    </outbound>
    <on-error>
        <base />
    </on-error>
</policies>

Karthikeyan Ramasamy 0 Reputation points Microsoft Employee

2024-07-11T12:58:54.1533333+00:00
@Ganti Sri Naga Sai Ajay Kamal

From the trace, The problem i notice is secondary URL is again getting overridden.

Check the effective policy once.

Below policy worked fine for me. Try using it from another operation, collect trace and compare with non-working one trace. Should help you identify where things going wong.

<policies> <inbound /> <backend> <retry condition="@(context.Response.StatusCode == 429)" count="1" interval="1" first-fast-retry="true"> <choose> <when condition="@(context.Response.StatusCode == 429)"> <set-backend-service base-url="https://test.org/" /> </when> </choose> <forward-request /> </retry> </backend> <outbound /> <on-error /> </policies>
Ganti Sri Naga Sai Ajay Kamal 0 Reputation points

2024-07-11T14:00:53.0366667+00:00

Thanks Karthikeyan for the solution. I found the issue already and fixed it. In the global policy (i mean policy for all HTTP operations) the inbound it is set to primary backend server which is overriding the policy i have set for this specific HTTP method.

Share via

Azure APIM Policy to failover primary backend URL to secondary in case of a status code 429