Azure APIM - how to send trace from within policy expression? - azure

Question

I have the below policy in Azure API Management. It works fine like that:
<return-response>
<set-status code="302" />
<set-header name="Location" exists-action="override">
<value>#{
try
{
// ... doing something here that might throw an Exception
return "http://example.com";
}
catch (Exception e)
{
// If something failed, it is usually because of an transient error. Then we just send the user to the same URL again to retry.
return "/";
}
}</value>
</set-header>
</return-response>
Now I would like to log/trace a message inside the Catch block. Basically something like this, but this of course does not work.
catch (Exception e)
{
<trace source="MyApi" severity="error">
<message>Error foo</message>
<metadata name="ErrorMessage" value="#(e.Message)"/>
</trace>
return "/";
}
How can I do this or how otherwise send logs to the connected Application Insights instance?

Answer 1

You let <on-error> section handle the tracing:
<policies>
<inbound>
<base />
<return-response>
<set-status code="302" />
<set-header name="Location" exists-action="override">
<value>#{
int d = 0;
int result = 42 / d;
return result.ToString();
}</value>
</set-header>
</return-response>
</inbound>
<backend>
<base />
</backend>
<outbound>
<base />
</outbound>
<on-error>
<base />
<trace source="ErrorInformation" severity="error">
<message>ErrorInformation</message>
<metadata name="EsbCorrelationId" value="#((!context.Variables.ContainsKey("esb-correlation-id") || context.Variables.GetValueOrDefault<string>("esb-correlation-id").Equals(string.Empty)) ? "-none-" : context.Variables.GetValueOrDefault<string>("esb-correlation-id"))" />
<metadata name="IpAddress" value="#(context.Request.IpAddress.ToString())" />
<metadata name="LastError.Source" value="#((context.LastError.Source == null || context.LastError.Source.Equals(string.Empty)) ? "-none-" : context.LastError.Source.ToString())" />
<metadata name="LastError.Reason" value="#((context.LastError.Reason == null || context.LastError.Reason.Equals(string.Empty)) ? "-none-" : context.LastError.Reason.ToString())" />
<metadata name="LastError.Message" value="#((context.LastError.Message == null || context.LastError.Message.Equals(string.Empty)) ? "-none-" : context.LastError.Message.ToString())" />
<metadata name="LastError.Scope" value="#((context.LastError.Scope == null || context.LastError.Scope.Equals(string.Empty)) ? "-none-" : context.LastError.Scope.ToString())" />
<metadata name="LastError.Section" value="#((context.LastError.Section == null || context.LastError.Section.Equals(string.Empty)) ? "-none-" : context.LastError.Section.ToString())" />
<metadata name="LastError.Path" value="#((context.LastError.Path == null || context.LastError.Path.Equals(string.Empty)) ? "-none-" : context.LastError.Path.ToString())" />
<metadata name="LastError.PolicyId" value="#((context.LastError.PolicyId == null || context.LastError.PolicyId.Equals(string.Empty)) ? "-none-" : context.LastError.PolicyId.ToString())" />
</trace>
</on-error>
</policies>
which will give you an entry in traces with this content in customDimensions:
LastError.Message
Expression evaluation failed. Attempted to divide by zero.
LastError.Path
return-response
LastError.PolicyId
-none-
LastError.Reason
ExpressionValueEvaluationFailure
LastError.Scope
operation
LastError.Section
inbound
LastError.Source
set-header