- Getting Started
- Support for K8s Installers
- Deploying on Kind
- Deploying on Minikube
- Installing with Helm
- Antrea Network Policy
- Traffic Encryption (Ipsec / WireGuard)
- Securing Control Plane
- Security considerations
- OS-specific Known Issues
- OVS Pipeline
- Feature Gates
- Antrea Proxy
- Network Flow Visibility
- Traceflow Guide
- NoEncap and Hybrid Traffic Modes
- Egress Guide
- NodePortLocal Guide
- Antrea IPAM Guide
- Exposing Services of type LoadBalancer
- Traffic Control
- Antrea API Groups
- Antrea API Reference
Antrea Multi-cluster Architecture
Antrea Multi-cluster implements Multi-cluster Service API, which allows users to create multi-cluster Services that can be accessed cross clusters in a ClusterSet. Antrea Multi-cluster also supports Antrea ClusterNetworkPolicy replication. Multi-cluster admins can define ClusterNetworkPolicies to be replicated across the entire ClusterSet, and enforced in all member clusters.
An Antrea Multi-cluster ClusterSet includes a leader cluster and multiple member clusters. Antrea Multi-cluster Controller needs to be deployed in the leader and all member clusters. A cluster can serve as the leader, and meanwhile also be a member cluster of the ClusterSet.
The diagram below depicts a basic Antrea Multi-cluster topology with one leader cluster and two member clusters.
ClusterSet is a placeholder name for a group of clusters with a high degree of mutual trust and shared ownership that share Services amongst themselves. Within a ClusterSet, Namespace sameness applies, which means all Namespaces with a given name are considered to be the same Namespace. The ClusterSet Custom Resource Definition(CRD) defines a ClusterSet including the leader and member clusters information.
The ClusterClaim CRD is used to claim a ClusterSet with a unique ClusterSet ID, and to claim the cluster itself as a member of a ClusterSet with a unique cluster ID.
The MemberClusterAnnounce CRD declares a member cluster configuration to the leader cluster.
The Common Area is an abstraction in the Antrea Multi-cluster implementation provides a storage interface for resource export/import that can be read/written by all member and leader clusters in the ClusterSet. The Common Area is implemented with a Namespace in the leader cluster for a given ClusterSet.
Antrea Multi-cluster Controller
Antrea Multi-cluster Controller implements ClusterSet management and resource export/import in the ClusterSet. In either a leader or a member cluster, Antrea Multi-cluster Controller is deployed with a Deployment of a single replica, but it takes different responsibilities in leader and member clusters.
In a member cluster, Multi-cluster Controller watches and validates the ClusterSet and ClusterClaim CRs, and creates a MemberClusterAnnounce CR in the Common Area of the leader cluster to join the ClusterSet.
In the leader cluster, Multi-cluster controller watches and validates the ClusterSet and Clusterclaim CRs, and initializes the ClusterSet. It also validates the MemberClusterAnnounce CR created by a member cluster and adds the cluster to the ClusterSet CR’s member cluster list.
Resource Export and Import
In a member cluster, Multi-cluster controller watches exported resources (e.g. ServiceExports, Services, Multi-cluster Gateways), encapsulates an exported resource into a ResourceExport and creates the ResourceExport CR in the Common Area of the leader cluster.
In the leader cluster, Multi-cluster Controller watches ResourceExports created by member clusters (in the case of Service and ClusterInfo export), or by the ClusterSet admin (in the case of Multi-cluster NetworkPolicy), converts ResourceExports to ResourceImports, and creates the ResourceImport CRs in the Common Area for member clusters to import them. Multi-cluster Controller also merges ResourceExports from different member clusters to a single ResourceImport, when these exported resources share the same kind, name, and original Namespace (matching Namespace sameness).
Multi-cluster Controller in a member cluster also watches ResourceImports in the Common Area of the leader cluster, decapsulates the resources from them, and creates the resources (e.g. Services, Endpoints, Antrea ClusterNetworkPolicies, ClusterInfoImports) in the member cluster.
For more information about multi-cluster Service export/import, please also check the Service Export and Import section.
Service Export and Import
Antrea Multi-cluster Controller implements Service export/import among member clusters. The above diagram depicts Antrea Multi-cluster resource export/import pipeline, using Service export/import as an example.
Given two Services with the same name and Namespace in two member clusters -
foo.ns.cluster-b.local, a multi-cluster Service can
be created by the following resource export/import workflow.
- User creates a ServiceExport
nsin each of the two clusters.
- Multi-cluster Controllers in
foo, and both create two ResourceExports for the Service and Endpoints respectively in the Common Area of the leader cluster.
- Multi-cluster Controller in the leader cluster sees the ResourcesExports in
the Common Area, including the two for Service
cluster-b-ns-foo-service; and the two for the Endpoints:
cluster-b-ns-foo-endpoints. It then creates a ResourceImport
ns-foo-servicefor the multi-cluster Service; and a ResourceImport
ns-foo-endpointsfor the Endpoints, which includes the exported endpoints of both
- Multi-cluster Controller in each member cluster watches the ResourceImports
from the Common Area, decapsulates them and gets Service
ns/antrea-mc-foo, and creates the Service and Endpoints, as well as a ServiceImport
fooin the local Namespace
Service Access Across Clusters
Since Antrea v1.7.0, the Service’s ClusterIP is exported as the multi-cluster Service’s Endpoints. Multi-cluster Gateways must be configured to support multi-cluster Service access across member clusters, and Service CIDRs cannot overlap between clusters. Please refer to Multi-cluster Gateway for more information. Before Antrea v1.7.0, Pod IPs are exported as the multi-cluster Service’s Endpoints. Pod IPs must be directly reachable across clusters for multi-cluster Service access, and Pod CIDRs cannot overlap between clusters. Antrea Multi-cluster only supports creating multi-cluster Services for Services of type ClusterIP.
Antrea started to support Multi-cluster Gateway since v1.7.0. User can choose one K8s Node as the Multi-cluster Gateway in a member cluster. The Gateway Node is responsible for routing all cross-clusters traffic from the local cluster to other member clusters through tunnels. The diagram below depicts Antrea Multi-cluster connectivity with Multi-cluster Gateways.
Antrea Agent is responsible for setting up tunnels between Gateways of member clusters. The tunnels between Gateways use Antrea Agent’s configured tunnel type. All member clusters in a ClusterSet need to deploy Antrea with the same tunnel type.
The Multi-cluster Gateway implementation introduces two new CRDs
Gateway includes the local Multi-cluster Gateway
internalIP for tunnels to local Nodes, and
for tunnels to remote cluster Gateways.
ClusterInfoImport includes Gateway
and network information of member clusters, including Gateway IPs and Service
CIDRs. The existing esource export/import pipeline is leveraged to exchange
the cluster network information among member clusters, generating
ClusterInfoImports in each member cluster.
Multi-cluster Service Traffic Walk
Let’s use the ClusterSet in the above diagram as an example. As shown in the diagram:
- Cluster A has a client Pod named
pod-arunning on a regular Node, and a multi-cluster Service named
- Cluster B exported a Service named
defaultNamespace. The Service has one Endpoint
- Cluster C exported a Service named
10.11.12.33also in the
defaultNamespace. The Service has one Endpoint
The multi-cluster Service
antrea-mc-nginx in cluster A will have two
10.96.2.22from cluster B.
10.11.12.33from cluster C.
When the client Pod
pod-a on cluster A tries to access the multi-cluster
antrea-mc-nginx, the request packet will first go through the Service
load balancing pipeline on the source Node
node-a2, with one endpoint of the
multi-cluster Service being chosen as the destination. Let’s say endpoint
10.11.12.33 from cluster C is chosen, then the request packet will be DNAT’d
10.11.12.33 and tunnelled to the local Gateway Node
node-a1 knows from the destination IP (
10.11.12.33) the packet is
multi-cluster Service traffic destined for cluster C, and it will tunnel the
packet to cluster C’s Gateway Node
node-c1, after performing SNAT and setting
the packet’s source IP to its own Gateway IP. On
node-c1, the packet will go
through the Service load balancing pipeline again with an endpoint of Service
nginx being chosen as the destination. As the Service has only one endpoint -
pod-c, the request packet will be DNAT’d to
and tunnelled to
pod-c is running. Finally, on
packet will go through the normal Antrea forwarding pipeline and be forwarded
Antrea Multi-cluster NetworkPolicy
At this moment, Antrea does not support Pod-level policy enforcement for
cross-cluster traffic. Access towards multi-cluster Services can be regulated
with Antrea ClusterNetworkPolicy
toService rules. In each member cluster,
users can create an Antrea ClusterNetworkPolicy selecting Pods in that cluster,
with the imported Mutli-cluster Service name and Namespace in an egress
toService rule, and the Action to take for traffic matching this rule.
For more information regarding Antrea ClusterNetworkPolicy (ACNP), refer
Multi-cluster admins can also specify certain ClusterNetworkPolicies to be replicated across the entire ClusterSet. The ACNP to be replicated should be created as a ResourceExport in the leader cluster, and the resource export/import pipeline will ensure member clusters receive this ACNP spec to be replicated. Each member cluster’s Multi-cluster Controller will then create an ACNP in their respective clusters.
Antrea Traffic Modes
Multi-cluster Gateway supports all of
networkPolicyOnly modes. In all supported modes, the cross-cluster traffic
is routed by Multi-cluster Gateways of member clusters, and the traffic goes
through Antrea overlay tunnels between Gateways. In
networkPolicyOnly modes, even when in-cluster Pod traffic does not go through
tunnels, antrea-agent still creates tunnels between the Gateway Node and other
Nodes, and routes cross-cluster traffic to reach the Gateway through the tunnels.
networkPolicyOnly mode, Antrea only
handles multi-cluster traffic routing, while the primary CNI takes care of in-cluster