Knowledge Base

External hosts are not resolved from a Plesk server: “Name or service not known” or “Could not resolve host”

nginx fails to start with the error message:

nginx[58503]: nginx: [warn] "ssl_stapling" ignored, host not found in OCSP responder "r3.o.lencr.org" in the certificate "/usr/local/psa/var/certificates/scfO1mntc"
When securing a domain with a Let's Encrypt certificate, the operation fails with:

Could not issue a Let's Encrypt SSL/TLS certificate for example.com
Failed to connect to the Let's Encrypt server https://acme-v01.api.letsencrypt.org.
Please try again later or report the issue to support.

Details

Could not obtain directory:
When installing a Plesk license, the operation fails with:

cURL cannot communicate with license server https://id-00.kaid.plesk.com:443/ (): Couldn't resolve host name(6) cURL cannot communicate with license server https://id-00.kaid.plesk.com:443/ (): Couldn't resolve host name(6) (Error code: 2)

Could not update the license. Make sure that connections to the license server ka.plesk.com on TCP port 443 are not blocked. See how to do so.
On attempt to connect to any external host using the cURL utility, the command shows:

# curl -I http://example.com
curl: (6) Could not resolve host: example.com

The DNS resolver specified in the file /etc/resolv.conf cannot resolve domain names.

Connect to the Plesk server via SSH.
Open the file /etc/resolv.conf in a text editor. In this example, we are using the vi editor:

# vi /etc/resolv.conf
Comment out the invalid resolver by placing a # (hash) character at the beginning of the line:

#nameserver 203.0.113.2
Add a different DNS resolver, for example Cloudflare DNS:

nameserver 1.1.1.1
Save the change and close the file.

Note: /etc/resolv.conf can be overwritten on Ubuntu 18.04 and higher by netplan and systemd-resolved.services.
Retry the previously failed operation.

Note: If the above solution does not help, contact your service provider in order to check the network setup.