CentOS Starting new HTTPS connection (1): acme-v01.api.letsencrypt.org An unexpected error occurred:

While running certonly command I got following error:
[root@vps147238 letsencrypt]# certbot --apache certonly --cert-name purabtech.com -d purabtech.in
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator apache, Installer apache
Starting new HTTPS connection (1): acme-v01.api.letsencrypt.org
An unexpected error occurred:
ConnectionError: (‘Connection aborted.’, gaierror(-2, ‘Name or service not known’))
Please see the logfiles in /var/log/letsencrypt for more details.

I solved this issue by doing following:

$vi /etc/letsencrypt/cli.ini

Put following code in that
server = https://acme-v02.api.letsencrypt.org/directory

It solved my problem…