Question

I got URI error notification for /crossdomain.xml at dashboard in admin console of appengine.

• How to fix the error?

Answer 1

From Adobe’s site:

A cross-domain policy file is an XML document that grants a web
client—such as Adobe Flash Player, Adobe Reader, etc.—permission to
handle data across multiple domains. When a client hosts content from
a particular source domain and that content makes requests directed
towards a domain other than its own, the remote domain would need to
host a cross-domain policy file that grants access to the source
domain, allowing the client to continue with the transaction. Policy
files grant read access to data, permit a client to include custom
headers in cross-domain requests, and are also used with sockets to
grant permissions for socket-based connections.

crossdomain.xml is an example of this type of cross-domain policy file.

In the context of your site, someone (maybe you, maybe someone else) is trying to access content from your site from within an Adobe application. The application, trying to be a good citizen, is checking for the existence of a cross-domain policy file before performing the actions. Since you haven’t provided one, you’re getting a 404 in your log.

The easiest fix is to write a crossdomain.xml file, and serve it from your App Engine app. Adobe apps that are looking for it will now get a file instead of a 404 and the error will stop appearing in your log.

Alternatively, you can just ignore the error. Like with a missing robots.txt file, the 404 errors aren’t doing damage to your site, they are just occasionally populating your logs with errors you don’t care about.