Symptoms

Website is not accessible:

• Firefox: Server not found
• Opera: Could not locate remote server
• Internet Explorer: Internet Explorer cannot display the webpage or shows This page can’t be displayed message
• Google Chrome: This site can’t be reached

Requesting the website over HTTP and shows redirection to HTTPS:

# curl -I http://www.example.com/ -v
* About to connect() to www.example.com port 80 (#0)
*  Trying 203.0.113.2... connected
* Connected to www.example.com (203.0.113.2) port 80 (#0)
> HEAD / HTTP/1.1
> User-Agent: curl/7.19.7 (x86_64-redhat-linux-gnu) libcurl/7.19.7 NSS/3.27.1 zlib/1.2.3 libidn/1.18 libssh2/1.4.2
> Host: www.example.com
> Accept: */*
>
< HTTP/1.1 303 See Other
HTTP/1.1 303 See Other
< Content-Length: 152
Content-Length: 152
< Content-Type: text/html; charset=UTF-8
Content-Type: text/html; charset=UTF-8
< Location: https://www.example.com/
Location: https://www.example.com/​   
< Server: Microsoft-IIS/7.5
Server: Microsoft-IIS/7.5

Requesting the website over HTTP shows SSL connection error:

# curl -k https://www.example.com/ -v
* About to connect() to www.example.com port 443 (#0)
*  Trying 203.0.113.2... connected
* Connected to www.example.com (203.0.113.2) port 443 (#0)
* Initializing NSS with certpath: sql:/etc/pki/nssdb
* warning: ignoring value of ssl.verifyhost
* skipping SSL peer certificate verification
* SSL connection using TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA
* Server certificate:
*      subject: CN=secure.example.com,OU=Domain Control Validated,C=US
*      start date: Jan 21 18:55:48 2013 GMT
*      expire date: Jan 22 18:55:48 2014 GMT
*      common name: secure.example.com
*      issuer: CN=AlphaSSL CA - G2,O=AlphaSSL

Cause

Redirection to HTTPS is hardcoded in website code, but not enabled in Plesk.

Resolution

1. Login to the server over RDP or SSH

2. Go to Subscriptions > example.com > Domains & Websites > Hosting Settings and enable 'SSL\TLS support' option: