Acme:error:connection when redirecting authorization requests from IIS to nginx


Hi folks,

i am struggling for hours with getting lets encrypt run in my little cloud environment.
I have 2 machines:

  • One Ubuntu Box (which is my certificate server and manages all certificates for the cloud)
  • One Windows Server which is running IIS 8.5

Since I don’t want my windows server to deal with the certification process and process everything on my ubuntu box I have configured forwards in IIS on the acme-challenge path to redirect to my ubuntu box.
The ubuntu box is running nginx is able to handle certification requests for it’s own domain names e.g.
letsencrypt certonly -a webroot --webroot-path=/var/www/html -d

but when I call it with any of the configured domain names pointing to the windows server e.g.
letsencrypt certonly -a webroot --webroot-path=/var/www/html -d -d

i receive:
The server could not connect to the client to verify the domain :: Could not connect to,
Type: connection
Detail: Could not connect to

Any ideas what can cause this?
The redirect works in the browser as it should.

I also checked that all files get generated in the acme-challenge folder on by Ubuntu box.

If you want to try it out, here an example request:

I would really appreciate any help or suggestion that can lead to a solution.



I resolved the issue by using a subdomain instead of the IP address in my redirect. No idea why it works with it, but it’s all fine now.



if you still need help can you let us know how you configured the redirects. IIS has multiple methods so it may be a limitation with the method you are using



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