High Availability for Self-Managed Kubernetes Clusters at DT One


The engineering group at DT A single, a international provider of cell prime-up and reward alternatives, wrote about how they carried out IP-failover based higher availability for their self-managed Kubernetes cluster ingress on Hetzner’s internet hosting system.

DT A person runs their Kubernetes clusters on bare metallic equipment on Hetzner. The cluster has an nginx-primarily based Kubernetes ingress which exposes providers to the world wide web. After trying numerous approaches to reach higher-availability (HA) for the ingress nodes, they settled on a Puppet-automatic IP-failover based mostly remedy leveraging Hetzner’s “vSwitch” digital community.

Kubernetes clusters expose providers to exterior networks like the web by employing a Layer 7 (L7) ingress. Most cloud providers that provide managed Kubernetes also offer an ingress implementation with a load balancer. Having said that, self-managed Kubernetes ingresses commonly rely on nginx as a load balancer.

To add large-availability to these types of setups, Kubernetes needs a VIP + keepalived like remedy when there are many IPs exposed for exterior visitors. keepalived is a instrument that delivers HA utilizing the Digital Router Redundancy Protocol (VRRP) by switching a digital IP between hosts. For case in point, there may well be a number of ingress nodes that are configured in round-robin DNS. When a node fails, it has to be removed manually from DNS. If VIP is employed, the DNS identify will point to just a one IP (the virtual IP) and keepalived will make sure it generally details to a live node managing ingress. For cloud platforms like GCP, AWS and Azure that provide a load balancer, VIPs are pointless as the system takes care of offering an HA load balancer. On the other hand, on platforms exactly where the LB is managed by the customer, VIP can deliver HA.

InfoQ obtained in contact with Jan Hejl, DevOps Tech Lead at DT 1, to fully grasp a lot more about the answer.

Generally, the ingress ports are bound to the major host’s IP. Hetzner gives a failover IP attribute in which an IP deal with (or even a subnet) can be switched from 1 server to a further, irrespective of the server’s site within 60 seconds. The crew in the beginning utilised personalized Python scripts to switch Hetzner’s failover IPs among ingress nodes, managed by keepalived. They afterwards adopted a modified edition of an present resolution, but it experienced some negatives like currently being pressured to use encrypted VRRP and adhere to IPv4. The more recent VRRPv3 protocol supports IPv6, but encryption was not doable. Hejl points out the safety challenges:


A bare-metal machine from Hetzner is portion of a /29 or even a /26 subnet, so other individuals can sniff a little something (say, applying tcpdump) that is not section of their personal website traffic. Specially in the situation in which the IPs are inside of the exact subnet, spoofing the multicast IP address is not that challenging even even though you have executed matters like arp_disregard / rp_filter and so forth.


Considering that it is a self-managed L7 ingress, how does DT One protect against DDoS like assaults? Hejl points out that “Hetzner is the to start with level of protection and then there are our have firewalls.”

DT One particular uses Puppet for virtually every little thing, says Hejl, with Terraform for automating Hetzner virtual devices or AWS deployments. Puppet was also made use of to automate the original alternative. This was superseded by a function that Hetzner released final calendar year known as vSwitch. vSwitch allocates a separate Layer 2 (L2) community for client equipment, which implies that unencrypted VRRP website traffic will become achievable without the need of the protection concerns. On the other hand, there were being however difficulties with Hetzner’s failover IPs. The  time taken to mirror improvements (~30 seconds) across the community was much too extended, and it was prone to any outages that could happen at Hetzner.

The crew at last arrived at a doing work remedy utilizing keepalived and 3 bodily hosts that converse in excess of a separate vSwitch network, automated employing Puppet. Each individual of the nodes acts as a chief for the other two VIPs, with the remaining two as followers. keepalived supports e mail notifications when the position of a node variations. In addition, Hejl states, they use Prometheus, Grafana and Alertmanager for checking and alerting their programs.

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