Service unavailable, HTTP Error 503. The service is unavailable.

 Environment:

Wanted to publish some services with ADFS and WAP.

ADFS was placed in internal network while WAP was placed in DMZ.

ADFS was configured properly and the default page was accessible internally.

But was getting the following error, while trying the same from the external network.

Error:

Service unavailable, HTTP Error 503. The service is unavailable.

Reason:

TLS 1.0 was disabled on the ADFS server

Solution:

After enabling TLS 1.0 on the ADFS server, the issue was resolved. 

Note: As Registry changes are always critical, so before doing any registry changes, please take backup of your system.