.. _clustermesh: .. _gs_clustermesh:

Setting up Cluster Mesh

This is a step-by-step guide on how to build a mesh of Kubernetes clusters. This guide shows you how to connect the clusters together, enable pod-to-pod connectivity across all clusters, set up cross-cluster :ref:service discovery and load-balancing <gs_clustermesh_load_balancing> and finally enforce security policies to restrict access.

.. admonition:: Video :class: attention

Aside from this step-by-step guide, if you would like to watch how Cilium's Clustermesh feature works, check out eCHO Episode 41: Cilium Clustermesh <https://www.youtube.com/watch?v=VBOONHW65NU&t=342s>__.

Prerequisites #############

Cluster Addressing Requirements

All clusters must be configured with the same datapath mode. Cilium install may default to :ref:arch_overlay or :ref:native_routing mode depending on the specific cloud environment.
PodCIDR ranges in all clusters and all nodes must be non-conflicting and unique IP addresses.
Nodes in all clusters must have IP connectivity between each other using the configured InternalIP for each node. This requirement is typically met by establishing peering or VPN tunnels between the networks of the nodes of each cluster.
The network between clusters must allow the inter-cluster communication. The exact ports are documented in the :ref:firewall_requirements section.

.. note::

For cloud-specific deployments, the following guides show how to meet the above requirements:

.. toctree:: :maxdepth: 1

 aks-clustermesh-prep
 eks-clustermesh-prep
 gke-clustermesh-prep

Additional Requirements for Native-routed Datapath Modes

Cilium in each cluster must be configured with a native routing CIDR that covers all the PodCIDR ranges across all connected clusters. Cluster CIDRs are typically allocated from the 10.0.0.0/8 private address space. When this is the case a native routing CIDR such as 10.0.0.0/8 should cover all clusters:
ConfigMap option ipv4-native-routing-cidr=10.0.0.0/8
Helm option --set ipv4NativeRoutingCIDR=10.0.0.0/8
cilium install option --set ipv4NativeRoutingCIDR=10.0.0.0/8
In addition to nodes, pods in all clusters must have IP connectivity between each other. This requirement is typically met by establishing peering or VPN tunnels between the networks of the nodes of each cluster
The network between clusters must allow pod-to-pod inter-cluster communication across any ports that the pods may use. This is typically accomplished with firewall rules allowing pods in different clusters to reach each other on all ports.

Scaling Limitations

By default, the maximum number of clusters that can be connected together using Cluster Mesh is 255. By using the option maxConnectedClusters this limit can be set to 511, at the expense of lowering the maximum number of cluster-local identities. Reference the following table for valid configurations and their corresponding cluster-local identity limits:

+------------------------+------------+----------+----------+ | MaxConnectedClusters | Maximum cluster-local identities | +========================+============+==========+==========+ | 255 (default) | 65535 | +------------------------+------------+----------+----------+ | 511 | 32767 | +------------------------+------------+----------+----------+

All clusters across a Cluster Mesh must be configured with the same maxConnectedClusters value.
ConfigMap option max-connected-clusters=511
Helm option --set clustermesh.maxConnectedClusters=511
cilium install option --set clustermesh.maxConnectedClusters=511

.. note::

This option controls the bit allocation of numeric identities and will affect the maximum number of cluster-local identities that can be allocated. By default, cluster-local :ref:security_identities are limited to 65535, regardless of whether Cluster Mesh is used or not.

.. warning:: MaxConnectedClusters can only be set once during Cilium installation and should not be changed for existing clusters. Changing this option on a live cluster may result in connection disruption and possible incorrect enforcement of network policies

Install the Cilium CLI

.. include:: ../../installation/cli-download.rst

.. warning::

Don't use the Cilium CLI helm mode to enable Cluster Mesh or connect clusters configured using the Cilium CLI operating in classic mode, as the two modes are not compatible with each other.

Prepare the Clusters ####################

For the rest of this tutorial, we will assume that you intend to connect two clusters together with the kubectl configuration context stored in the environment variables $CLUSTER1 and $CLUSTER2. This context name is the same as you typically pass to kubectl --context.

Specify the Cluster Name and ID

Cilium needs to be installed onto each cluster.

Each cluster must be assigned a unique human-readable name as well as a numeric cluster ID (1-255). The cluster name must respect the following constraints:

It must contain at most 32 characters;
It must begin and end with a lower case alphanumeric character;
It may contain lower case alphanumeric characters and dashes between.

It is best to assign both the cluster name and the cluster ID at installation time:

ConfigMap options cluster-name and cluster-id
Helm options cluster.name and cluster.id
Cilium CLI install options --set cluster.name and --set cluster.id

Review :ref:k8s_install_quick for more details and use cases.

Example install using the Cilium CLI:

.. code-block:: shell-session

cilium install --set cluster.name=$CLUSTER1 --set cluster.id=1 --context $CLUSTER1 cilium install --set cluster.name=$CLUSTER2 --set cluster.id=2 --context $CLUSTER2

.. important::

If you change the cluster ID and/or cluster name in a cluster with running workloads, you will need to restart all workloads. The cluster ID is used to generate the security identity and it will need to be re-created in order to establish access across clusters.

Shared Certificate Authority

If you are planning to run Hubble Relay across clusters, it is best to share a certificate authority (CA) between the clusters as it will enable mTLS across clusters to just work.

You can propagate the CA copying the Kubernetes secret containing the CA from one cluster to another:

.. code-block:: shell-session

kubectl --context=$CLUSTER1 get secret -n kube-system cilium-ca -o yaml |
kubectl --context $CLUSTER2 create -f -

.. _enable_clustermesh:

Enable Cluster Mesh

Enable all required components by running cilium clustermesh enable in the context of both clusters. This will deploy the clustermesh-apiserver into the cluster and generate all required certificates and import them as Kubernetes secrets. It will also attempt to auto-detect the best service type for the LoadBalancer to expose the Cluster Mesh control plane to other clusters.

.. code-block:: shell-session

cilium clustermesh enable --context $CLUSTER1 cilium clustermesh enable --context $CLUSTER2

.. important::

In some cases, the service type cannot be automatically detected and you need to specify it manually. This can be done with the option --service-type. The possible values are:

LoadBalancer: A Kubernetes service of type LoadBalancer is used to expose the control plane. This uses a stable LoadBalancer IP and is typically the best option.

NodePort: A Kubernetes service of type NodePort is used to expose the control plane. This requires stable Node IPs. If a node disappears, the Cluster Mesh may have to reconnect to a different node. If all nodes have become unavailable, you may have to re-connect the clusters to extract new node IPs.

ClusterIP: A Kubernetes service of type ClusterIP is used to expose the control plane. This requires the ClusterIPs are routable between clusters. This is typically only available via the helm chart installation method.

Wait for the Cluster Mesh components to come up by invoking cilium clustermesh status --wait. If you are using a service of type LoadBalancer then this will also wait for the LoadBalancer to be assigned an IP.

.. code-block:: shell-session

cilium clustermesh status --context $CLUSTER1 --wait cilium clustermesh status --context $CLUSTER2 --wait

.. code-block:: shell-session

✅ Cluster access information is available:
  - 10.168.0.89:2379
✅ Service "clustermesh-apiserver" of type "LoadBalancer" found
🔌 Cluster Connections:

Connect Clusters

Finally, connect the clusters. This step only needs to be done in one direction. The connection will automatically be established in both directions:

.. code-block:: shell-session

cilium clustermesh connect --context $CLUSTER1 --destination-context $CLUSTER2

It may take a bit for the clusters to be connected. You can run cilium clustermesh status --wait to wait for the connection to be successful:

.. code-block:: shell-session

cilium clustermesh status --context $CLUSTER1 --wait

The output will look something like this:

.. code-block:: shell-session

✅ Cluster access information is available:
  - 10.168.0.89:2379
✅ Service "clustermesh-apiserver" of type "LoadBalancer" found
⌛ Waiting (12s) for clusters to be connected: 2 nodes are not ready
⌛ Waiting (25s) for clusters to be connected: 2 nodes are not ready
⌛ Waiting (38s) for clusters to be connected: 2 nodes are not ready
⌛ Waiting (51s) for clusters to be connected: 2 nodes are not ready
⌛ Waiting (1m4s) for clusters to be connected: 2 nodes are not ready
⌛ Waiting (1m17s) for clusters to be connected: 1 nodes are not ready
✅ All 2 nodes are connected to all clusters [min:1 / avg:1.0 / max:1]
🔌 Cluster Connections:
- cilium-cli-ci-multicluster-2-168: 2/2 configured, 2/2 connected

If this step does not complete successfully, proceed to the troubleshooting section.

Test Pod Connectivity Between Clusters

Congratulations, you have successfully connected your clusters together. You can validate the connectivity by running the connectivity test in multi cluster mode:

.. code-block:: shell-session

cilium connectivity test --context $CLUSTER1 --multi-cluster $CLUSTER2

Next Steps

Logical next steps to explore from here are:

:ref:gs_clustermesh_load_balancing
:ref:gs_clustermesh_network_policy

Troubleshooting ###############

Use the following list of steps to troubleshoot issues with ClusterMesh:

#. Validate that Cilium pods are healthy and ready:

.. code-block:: shell-session

   cilium status --context $CLUSTER1
   cilium status --context $CLUSTER2

#. Validate that Cluster Mesh is enabled and operational:

.. code-block:: shell-session

   cilium clustermesh status --context $CLUSTER1
   cilium clustermesh status --context $CLUSTER2

If you cannot resolve the issue with the above commands, see the :ref:troubleshooting_clustermesh for a more detailed troubleshooting guide.