I am supporting ASP.NET application running on 3 web servers and have F5 system as firewall and load balance. Actually I don't have experience at all in F5 system but the following issue seems to be related to it
The issue happened after we applied F5 load balancing. Simply it cause JavaScript in the web page to fail sometimes. After refresh the web page it will work fine
To trace the issue I compared the response that fail and the one that success after refresh. The difference was the failed one contains html tag that is not added by our application apm_do_not_touch with a script tag inside it
It seems that happen when the F5 switch between one server to another one as the issue solved when we redirect all the traffic to only one server
Any advice, what is the possible cause and how we can solve it?
APM is F5's Access Policy Manager module and is used for VPN, Web Portals, and federated authentication. The apm_do_not_touch tag is part of this product and is used when you want to prevent the APM module from rewriting portions of HTML such as external links.
If you're not accessing the application through a web portal, this should not be applied and you'll need to work with whomever setup the access policy to resolve as the APM policy is being applied to your application possibly erroneously.
Here is more information on the apm_do_not_touch tag. Depending on your version, there was a known issue for @cc_on in F5 BIG-IP version 11.1 who's workaround was to prevent the APM module from rewriting that command. The same workaround may pose a solution for you. Either way, there are additional complexities to your client traffic flow that you will need to engage your network team/BIG-IP administrators with to ensure your application and their policies don't clash.
It could be as simple as removing the APM policy from your application's pathway but your admins will be able to identify if it's required for external access or reverse proxy requirements.