We had a working ADFS server farm serving production office 365 single sign on environment for one of our clients. Suddently users reported that they are at times getting Office 365 login was given error “HTTP Error 503” while redirecting to ADFS page. Before that there were some issues with authentication of some outlook and Mobil clients as well however it was again sporadic.
We had a Two windows 2008 R2 server installed with the latest version of ADFS from O365 behind a hardware Load Balancer and along with that the usual Active directory domain infrastructure with over 20 domain controllers.
It was quite evident that the issue is with ADFS server as, first there were no other issues reported inside the orgnization and second we were seeing Http Error 503 every now and then, which was definitely atleast starting from ADFS server. Hence, To Begin troubleshooting the issue, its best to try and isolate the cause by individually trying to sign into both the server internally, the one which gives the issue is causing the problem. like this
https://<ADFS server 1>/adfs/ls/IdpInitiatedSignon.aspx
https:// <ADFS server 2>/adfs/ls/IdpInitiatedSignon.aspx
If one of the server gives error like “HTTP Error 503”,problem with that server. As an immidiate solution we can try to remove it from the load balancer by the time we resolve the issue, so that external users do not run into this server causing the error
We started to look around to find the issue and not too later we found that ADFSAppPool was down on one of the server, started it to resolve the issue
Hope this helps you fix the issue, else you can always reach out to us for paid support, here
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