I am running a bare metal Kubernetes cluster on k3s with Kube-VIP and Traefik. This works great for services that use SSL/TLS as Server Name Indication (SNI) can be used to reverse proxy multiple services listening on the same port. Consequently, getting Traefik to route multiple web servers receiving traffic on ports 80 or 443 is not a problem at all. However, I am stuck trying to accomplish the same thing for services that just use TCP or UDP without SSL/TLS since SNI is not included in TCP or UDP traffic.
I tried to setup Forgejo where clients will expect to use commands like git clone git@my.forgejo.instance.... which would ultimately use SSH on port 22. Since SSH uses TCP and Traefik supports TCPRoutes, I should be able to route traffic to Forgejo’s SSH entry point using port 22, but I ran into an issue where the SSH service on the node would receive/process all traffic received by the node instead of allowing Traefik to receive the traffic and route it. I believe that I should be able to change the port that the node’s SSH service is listening on or restrict the IP address that the node’s SSH service is listening on. This should allow Traefik to receive the traffic on port 22 and route that traffic to Forgejo’s SSH entry point while also allowing me to SSH directly into the node.
However, even if I get that to work correctly, I will run into another issue when other services that typically run on port 22 are stood up. For example, I would not be able to have Traefik reverse proxy both Forgejo’s SSH entry point and an SFTP’s entry point on port 22 since Traefik would only be able to route all traffic on port 22 to just one service due to the lack of SNI details.
The only viable solution that I can find is to only run one service’s entry point on port 22 and run each of the other services’ entry points on various ports. For instance, Forgejo’s SSH entry point could be port 22 and the SFTP’s entry point could be port 2222 (mapped to the pod’s port 22). This would require multiple additional ports be opened on the firewall and each client would need its configuration and/or commands modified to connect to the service’s a non-standard port.
Another solution that I have seen is to use other services like stunnel to wrap traffic in TLS (similar to how HTTPS works), but I believe this will likely lead to even more problems than using multiple ports as every client would likely need to be compatible with those wrapper services.
Is there some other solution that I am missing? Is there something that I could do with Virtual IP addresses, multiple load balancer IP addresses, etc.? Maybe I could route traffic on Load_Balancer#1_IP_Address:22 to Forgejo’s SSH entry point and Load_Balancer#2_IP_Address:22 to SFTP’s entry point?
tl;dr: Is it possible to host multiple services that do not use SSL/TLS (ie: cannot use SNI) on the same port in a single Kubernetes cluster without using non-standard ports and port mapping?
I think I can avoid using metallb since I’m already using Kube-VIP.
I do not think that I am using Virtual IPs correctly as I tried setting it up, but it did not work. I assume the Virtual IP would just become the Load Balancer IP and I would need to configure Traefik and Kube-VIP (as well as my network) to use the Virtual IPs?
Ingress controllers like Traefik come across as LB services to IPAM modules like MetalLB (I’ve never used Kube-VIP but I suppose it’s the same story). These plug-ins assign IP addresses to these LB services.
You can assign a specific IP to an instance of an “outward-facing route” with labels. I don’t remember technical terms relevant to Ingresses because I’ve been messing with the Gateway API recently.
That all makes sense and tried setting it up that way but could not get it to work. I am not sure if it was an issue with my network, k3s, Kube-VIP, or Traefik (or some combination of them). I will try getting it to work again.
Even if I do though, I would run into an issue if I publicly exposed these services (I understand there are security implications of doing so). How would I route traffic received externally/publicly on port 22 to more than one IP address? I think I would only be able to do this for local/internal traffic by managing the local DNS.
Yeah, you’d have a LoadBalancer service for Traefik which gets assigned a VIP outside the cluster.
I’m already doing that, but just for one VIP. I think I just need to get the additional VIPs working.
I know that I will need to update my local network’s DNS so that something like service#1 = git.ssh.local.domain and git.ssh.local.domain = 192.168.50.10 and service#2 = sftp.local.domain and sftp.local.domain = 192.168.50.20. I would setup 192.168.50.10 as the load balancer IP address to Forgejo’s SSH entrypoint and 192.168.50.20 as the load balancer IP address to the SFTP’s entrypoint. However, how would I handle requests/traffic received externally? The router/firewall would receive everything and can port forward port 22 to a single IP address, which would prevent one (or more) service from being used externally, correct?
