Cilium uses a clustermesh-apiserver when multiple clusters are connected in clustermesh, or when external workloads are connected to the Cilium cluster. If neither is used, then clustermesh-apiserver is never required.

Since etcd is used in a clustermesh for data synchronization, an etcd server container is deployed within clustermesh-apiserver pod.

When used in an External Workloads setup, it also creates a CiliumNode and CiliumEndpoint resources for each workload name and allocates its identity.

Note: ipv4-alloc-cidr set in the CiliumExternalWorkload object spec is currently unused. IP address tied to the CiliumEndpoint and CiliumNode is the one that is registered by cilium-agent (IP address of the external workload).

The API server itself performs the following operations:

It performs the job of synchronizing CiliumIdentites, CiliumEndpoints, CiliumNodes and Kubernetes services from k8s datastore to the KVStore (etcd).

Cilium's heartbeat path key stored in the KVStore is periodically updated by the API server with the current time so that Cilium Agents can correctly validate KVStore updates. The key for this heartbeat is cilium/.heartbeat.

Clustermesh-apiserver is automatically deployed when External Workloads support or clustermesh is enabled using either Helm or the cilium-cli tool.

Users are required to set both cluster.name and a non-zero cluster.id in Helm or cilium install --cluster-name <name> --cluster-id <id>. Otherwise, clustermesh will not be correctly established.

clustermesh-apiserver service type defaults to NodePort. Depending on your k8s provider it may be beneficial to change this to LoadBalancer.

$ cilium clustermesh enable

$ cilium --context "${CONTEXT1}" clustermesh connect --destination-context "${CONTEXT2}"

Note: clustermesh connect command needs to be run for every new cluster (context) that joins clustermesh.

$ cilium --context "${CONTEXT1}" clustermesh status --wait

$ helm install cilium ... \
  --set clustermesh.useAPIServer=true \

Additionally, if your load balancer can give you a static IP address, it may be specified like so:

$ helm install cilium ... \
  --set clustermesh.apiserver.service.loadBalancerIP=xxx.xxx.xxx.xxx \

Clustermesh-apiserver is deployed as a standard k8s deployment with multiple containers. You can check that both clustermesh-apiserver and etcd server are present:

$ kubectl get pods -l k8s-app=clustermesh-apiserver \
  -o jsonpath='{range .items[*].spec.containers[*]}{.image}{"\n"}{end}'
quay.io/coreos/etcd:v3.5.4
quay.io/cilium/clustermesh-apiserver:v1.10.2

In helm installation clusters have to be connected in 2 steps:

1. Extract a cilium-clustermesh secret from each cluster to be applied in another cluster:

   $ contrib/k8s/k8s-extract-clustermesh-nodeport-secret.sh > cluster1-secret.json
   

   Repeat this step in all your clusters, storing the outputs into different files.

2. Apply secrets from all other clusters in each of your clusters, e.g., on cluster1:

   $ contrib/k8s/k8s-import-clustermesh-secrets.sh cluster2-secret.json cluster3-secret.json ...