Awwww – so much work I had put into setting up a Kubernetes cluster (this blog will run there in a few days). I set up the pods and containers, cron jobs, services, and, and, and. Then I started renewing my SSL certificates from LetsEncrypt. This renewal failed hilariously, but with a weird error message:
What? I can reach my websites. Did I miss something? I checked connectivity. The IP addresses were right, the ACME challenge directory was available as required by LetsEncrypt, the DNS was working properly. Why couldn’t LetsEncrypt servers not reach my cluster? I soon found out that they prefer IPv6 over IPv4 which I had both enabled. But the IPv6 connection failed. From everywhere. Ping6 though succeeded.
Further analysis revealed that Kubernetes is not able to expose IPv6 services at all (or at least at now, so I researched). What shall I do now? All my work was based on the assumption that IPv4 and IPv6 will be there. But it’s not with Kubernetes. Of course I could move my reverse proxy out of Kubernetes and put it in front of it. But that would require more work as all the automation scripts for LetsEncrypt would need to be rebased. Testing again and again. Let aside the disadvantage of not having it all self-contained in containers anymore. Another solution must be there.
Luckily there was an easy solution: socat. It’s a small Linux tool that can copy network traffic from one socket to another. So that was setup easily with a systemd script (sock_80.service):
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[Unit] Description=socat Service 80 After=network.target [Service] Type=simple User=root ExecStart=/usr/bin/socat -lf /var/log/socat80.log TCP6-LISTEN:80,reuseaddr,fork,bind=[ip6-address-goes-here] TCP4:ip4-address-goes-here:80 Restart=on-abort [Install] WantedBy=multi-user.target
That’s it. Enabled it (systemctl enable sock_80.service), reloaded systemd (systemctl daemon-reload), and started the service (systemctl start sock_80). Voilá! Here we go. IPv6 traffic is now routed to IPv4. I repeated it with port 443 and the setup is done. And LetsEncrypt servers are happy too 🙂