Websites are unavailable on a Plesk server: Unable to manage service by nginxmng

Symptoms

• All websites are down with the following error:

  This site can't be reached

• The following can be found at domains' log /var/www/vhosts/example.com/logs/proxy_error_log:

  436#0: *810 SSL_do_handshake() failed (SSL: error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol) while SSL handshaking to upstream

• It is not possible to restart the nginx service:

  # service nginx restart
  Unable to start service: Unable to manage service by nginxmng: ('start', 'nginx'). Error: ERR [util_exec] proc_close() failed ['/usr/local/psa/admin/bin/nginx_control' '--start'] with exit code [1] Error occured while sending feedback. HTTP code returned: 502 Error occured while sending feedback. HTTP code returned: 502 Can not start proxy server:

  ---

  nginx[21730]: nginx: [emerg] bind() to 203.0.113.2:443 failed (98: Address already in use)
  nginx[21730]: nginx: [emerg] bind() to 203.0.113.2:80 failed (98: Address already in use)

Cause

The nginx service was not stopped correctly.

Resolution

1. Connect to the Plesk server via SSH.

2. Re-enable Plesk nginx proxy using these commands:

   # /usr/local/psa/admin/bin/nginxmng -d
   # /usr/local/psa/admin/bin/nginxmng -e