Windows Admin Center is a web application that makes it easier to manage multiple servers via multiple Microsoft tools such System Center, RSAT, Intune, and PowerShell. If you install Windows Admin Center in an IIS server, you may come across “503 Service Unavailable” error.
Note: This post explains 503 error related to Windows Admin Center only. If the root cause is not this product, check this post out: HTTP 503 Service Unavailable (Application pool has been disabled)
Windows Admin Center works as gateway between clients and servers. Once it is installed, it redirects all HTTP traffic (port 80) to HTTPS port (443). Therefore, if you try to access that server via browser, you will reach to Windows Admin Center.
Source of the diagram above: What is Windows Admin Center?
Even if you uninstall it, the port 80 traffic still goes to Windows Admin Center. If you install IIS to that server and try to access localhost in your browser, you will see “503 Service Unavailable”. It’s because the server tries to load Windows Admin Center dashboard instead of IIS Default Web Site.
Solution for “503 Service Unavailable” error
In my case, I was able to solve this issue by removing the port 80 entries from the server. In order to do it, first list all entries by running the command below:
netsh http show urlacl
netsh http delete urlacl command for the entries with port 80. For example:
netsh http delete urlacl url=http://+:80/
If you are seeing 530 error while using IIS FTP, have a look at this post: 530 User cannot log in, home directory inaccessible