Add a blog on simple HA

Signed-off-by: Derek Nola <[email protected]>

blog/2025-01-06-simple-ha.md

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+---
+title: "The Basic HA Cluster"
+description: Creating the simplest High Availability cluster with LB and upgrading
+authors: dereknola # Fill out your info in the authors.yml file
+hide_table_of_contents: true
+# tags: ["hello"]
+---
+
+While we have more [detailed docs](/docs/ha/) on setting up a High Availability (HA) cluster, this post will cover the simplest HA cluster you can create. 
+
+<!-- truncate -->
+## Baseline HA Cluster 💻🖥️💻
+
+Whenever we get a question around HA, this is the cluster configuration I start with. It provides a solid foundation when deploying beyond a single server.
+
+Our cluster will have:
+- 4 nodes or VMs:
+    - 1 load balancer
+    - 3 servers
+- A k3s-upgrade plan that will automatically update the cluster to the latest patch version of a given minor.
+
+## Cluster Setup 🌐🔧
+
+I'm using `vagrant` to provision 4 Ubuntu 24.04 VMs for this setup, all on a flat network. Setup of nodes is left as an exercise for the reader 😅.
+
+My nodes are configured with the following names and IPs:
+| Name | IP |
+|------|----|
+| lb-0 | 10.10.10.100 |
+| server-0 | 10.10.10.50 |
+| server-1 | 10.10.10.51 |
+| server-2 | 10.10.10.52 |
+
+### Load Balancer
+
+I'm using [haproxy](https://www.haproxy.org/) as it supports later expansion to multiple LB nodes (via keepalived).
+
+SSH into the load balancer and install haproxy:
+
+```bash
+sudo apt install haproxy
+```
+
+The haproxy config is simple, just forward traffic to the servers:
+
+```
+#/etc/haproxy/haproxy.cfg
+frontend k3s
+    bind *:6443
+    mode tcp
+    default_backend k3s
+
+backend k3s
+    mode tcp
+    option tcp-check
+    balance roundrobin
+    server server-1 10.10.10.50:6443 check
+    server server-2 10.10.10.51:6443 check
+    server server-3 10.10.10.52:6443 check
+```
+
+Restart haproxy to apply the config:
+
+```bash
+systemctl restart haproxy
+```
+
+### Install K3s on first server
+
+On the first server, install K3s with embedded etcd and a known token:
+
+```bash
+curl -sfL https://get.k3s.io | INSTALL_K3S_CHANNEL=v1.31 sh -s - \
+--cluster-init --token k3sblog --tls-san 10.10.10.100
+```
+
+### Join the other servers
+
+On the other servers, join the cluster via the load balancer:
+
+```bash
+curl -sfL https://get.k3s.io | INSTALL_K3S_CHANNEL=v1.31 sh -s - \
+--server https://10.10.10.100:6443 --token k3sblog
+```
+
+### Grab the kubeconfig
+
+Now that the cluster is up, we can grab the kubeconfig from the first server:
+
+```bash
+scp server-0:/etc/rancher/k3s/k3s.yaml k3s.yaml
+```
+
+Modify it to access the cluster via the load balancer:
+
+```bash
+sed -i 's/127.0.0.1/10.10.10.100/' k3s.yaml
+```
+
+No we can manage the cluster from our local machine:
+
+```bash
+export KUBECONFIG=$(pwd)/k3s.yaml
+kubectl get nodes
+```
+
+## Upgrade Plan 🏗️📝📐
+
+The plan I'm using will keep k3s updated to the latest patch version of the channel we give. In this case I'm using the `v1.31` channel, the same channel used above. Kubernetes v1.31.4 just released at time of writing this post, so with this plan we have stable upgrades handled for the next 10-12 months (depending on how many patch releases this minor gets).
+
+### Install the system-upgrade-controller
+
+The upgrade plan is managed by the system-upgrade-controller. Install it:
+
+```bash
+kubectl apply -f https://github.com/rancher/system-upgrade-controller/releases/latest/download/system-upgrade-controller.yaml
+kubectl apply -f https://github.com/rancher/system-upgrade-controller/releases/latest/download/crd.yaml
+```
+
+### Create the upgrade plan
+```yaml
+#server-plan.yaml
+apiVersion: upgrade.cattle.io/v1
+kind: Plan
+metadata:
+  name: server-plan
+  namespace: system-upgrade
+spec:
+  concurrency: 1
+  cordon: true
+  nodeSelector:
+    matchExpressions:
+    - key: node-role.kubernetes.io/control-plane
+      operator: In
+      values:
+      - "true"
+  serviceAccountName: system-upgrade
+  upgrade:
+    image: rancher/k3s-upgrade
+  channel: https://update.k3s.io/v1-release/channels/v1.31
+```
+
+```bash
+kubectl apply -f server-plan.yaml
+```
+
+See the [automated upgrade docs](/docs/ha/automated-upgrades) for more details.
+
+
+## Conclusion 🚀
+
+![kubectl summary](kubectl.png)
+
+We now have a high-availability cluster, accessible via a single IP. Upgrades are handled for the next year. This is a great starting point to:
+- Add agent nodes to expand our workload capacity
+- Add another load-balancer for additional redundancy