Submariner consists of several main components that work in conjunction to securely connect workloads across multiple Kubernetes clusters.
For more information about Submariner’s architecture, please refer to the Architecture section.
The Broker is an API that all participating clusters are given access to, and where two objects are exchanged via CRDs in
- Cluster: defines a participating cluster and its IP CIDRs.
- Endpoint: defines a connection endpoint to a cluster, and the reachable cluster IPs from the endpoint.
The Broker must be deployed on a single Kubernetes cluster. This cluster’s API server must be reachable by all Kubernetes clusters connected
by Submariner. It can be a dedicated cluster, or one of the connected clusters.
The Submariner Deployment on a Cluster
Once Submariner is deployed on a cluster with the proper credentials to the Broker it will exchange Cluster and Endpoint objects with other
clusters (via push/pull/watching), and start forming connections and routes to other clusters.
Submariner has a few requirements to get started:
- At least two Kubernetes clusters, one of which is designated to serve as the central Broker that is accessible by all of your connected
clusters; this can be one of your connected clusters, or a dedicated cluster.
- The oldest tested Kubernetes version is 1.19.
Older versions are known not to work with Submariner. Service discovery requires Kubernetes 1.21 or later.
- Non-overlapping Pod and Service CIDRs between clusters. This is to prevent routing conflicts. For cases where addresses do
overlap, Globalnet can be set up.
- IP reachability between the gateway nodes. When connecting two clusters, the gateways must have at least one-way connectivity
to each other on their public or private IP address and encapsulation port. This is needed for creating the tunnels between
the clusters. The default encapsulation port is 4500/UDP, for NAT Traversal discovery port
4490/UDP is used.
For clusters behind corporate firewalls that block the default ports, Submariner also supports NAT Traversal
(NAT-T) with the option to set custom non-standard ports like 4501/UDP.
- Submariner uses UDP port 4800 to encapsulate Pod traffic from worker and master nodes to the Gateway nodes. This is required in order to
preserve the source IP addresses of the Pods. Ensure that firewall configuration allows 4800/UDP across all nodes in the cluster in both
directions. This is not a requirement when using OVN-Kubernetes CNI.
- If the gateway nodes are directly reachable over their private IPs without any NAT in between, ensure that firewall configuration allows
ESP protocol on the gateway nodes.
- Worker node IPs on all connected clusters must be outside of the Pod/Service CIDR ranges.
- Submariner can be deployed on x86-64 and ARM64 nodes.
(Submariner components are deployed on all nodes in the cluster,
so all nodes must be x86-64 or ARM64.)
An example of three clusters configured to use with Submariner (without Globalnet) would look like the following:
||Cluster Nodes CIDR
Submariner is designed to be cloud provider agnostic, and should run in any standard Kubernetes cluster. Submariner has been tested with the
following network (CNI) Plugins:
Submariner supports all currently-supported Kubernetes versions, as determined by the Kubernetes release policy.
Submariner is deployed and managed using its Operator. Submariner’s Operator can be
deployed using subctl or Helm.
The recommended deployment method is
subctl, as it is currently the default in CI and provides diagnostic features.