Multi-cluster mesh routing /w GitOps

This demo will build you 3 clusters that will all share their routing information with each other and forward DNS for cross-cluster Services.

The clusters are created using kind, and cluster0 is used as a Flux management cluster. Access to apply to the remaining clusters is done by mocking ClusterAPI kubeconfigs.

Discovery of other clusters' Nodes is accomplished through a fun bash controller that queries a multicast Serf cluster. This works well on a single docker network or any network that supports multicast. You can also configure Serf to bootstrap from some fixed IP's.

A neat thing about this strategy is that it's declarative! Fork this repo and try it out :)

Requirements:

• hub (optional)
• flux
• docker
• kind
• kubectl

Demo

kind/setup.sh
kind/load.sh

# bootstrap Calico for Flux
kubectl apply --context kind-cluster0 -k ./config/cluster0/kube-system
kubectl apply --context kind-cluster1 -k ./config/cluster0/kube-system
kubectl apply --context kind-cluster2 -k ./config/cluster0/kube-system

GITHUB_USER=adavarski
# set your own user here to match your fork

export GITHUB_TOKEN="<personal access token with repo and SSH key rights>"

kubectl config use-context kind-cluster0
flux bootstrap github \
  --owner "${GITHUB_USER}" \
  --personal \
  --repository "flux-multicluster-gitops" \
  --path "./config/cluster0"

kubectl config use-context kind-cluster1
flux bootstrap github \
  --owner "${GITHUB_USER}" \
  --personal \
  --repository "flux-multicluster-gitops" \
  --path "./config/cluster1"

kubectl config use-context kind-cluster2
flux bootstrap github \
  --owner "${GITHUB_USER}" \
  --personal \
  --repository "flux-multicluster-gitops" \
  --path "./config/cluster2"

alternatively, if you want to not use github & flux, apply the kube-system and default kustomizations to the proper clusters:

for cl in cluster{0..2}; do
  kubectl apply --context "kind-${cl}" -k "./config/${cl}/"{default,kube-system}
done

Looking around

• Get the Kustomization resources the cluster0 flux-system uses to apply to the other clusters
• Use the kubectl config use-context kind-{cluster0|cluster1|cluster2} to switch between kind-cluster0|1|2 on demand
• Check that the serf and calico dameonsets and deploys become ready
• Check out the Corefile ConfigMap extensions in kube-system
• Examine the BGPPeer resources that the serf-query controller created from the serf member list
• Exec into the debug pods for each cluster and run host podinfo.default.svc.cluster1.lan
• Try curling the service from and to different clusters!

Clean Up

kind/cleanup.sh

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More demos:

Flux's GPG signature verification and remote-cluster management over Cluster API: https://github.com/stealthybox/capi-flux-demo