How to: DNS configuration
If the message "This Jenkins instance appears to be offline." appears on first startup, and the container logs show lines such as `java.net.UnknownHostException: updates.jenkins.io`, your container may be having issues with resolving DNS names.

To potentially solve the issue, start the container specifying a dns server (for example Cloudflare's 1.1.1.1 or Google's 8.8.8.8, or any other DNS server):
```
docker run -p 8080:8080 -p 50000:50000 --restart=on-failure --dns 1.1.1.1 --dns 8.8.8.8 jenkins/jenkins:lts-jdk21
```