Modern applications are no longer confined to a single data center or cloud. For resilience, data sovereignty, or performance, they are increasingly distributed across multiple Kubernetes clusters that can be spread across different public clouds, on-premise data centers, and edge locations.
This distribution creates a significant challenge. While Kubernetes networking is brilliantly simple inside a single cluster, connecting a service in your AWS cluster to a database in your on-premise OpenShift cluster can be a networking nightmare. It often involves a complex tangle of VPNs, ingress gateways, firewall configurations, and IP address management.
Skupper, an open-source project, offers a radically simpler and more elegant solution. It is not a VPN or a complex networking layer, but a Layer 7 Service Interconnect designed to make multi-cluster communication easy, secure, and resilient.
How Skupper Works: The Virtual Application Network
Skupper’s approach is to abstract away the underlying network complexity entirely. It allows your distributed services to communicate as if they were all running in the same local cluster. It achieves this by creating a Virtual Application Network (VAN).
The process is simple:
- Deploy Skupper: You deploy a Skupper instance into each Kubernetes cluster you want to connect. These instances automatically discover each other and form a secure, peer-to-peer network of intelligent Layer 7 routers.
- Expose a Service: Using a simple command (skupper expose), you tell Skupper which service you want to share with the network. You don’t expose your whole cluster, only the specific services you choose.
- Connect Locally: This is the magic. When you expose a service in one cluster, Skupper automatically creates a local proxy for it in all the other connected clusters. An application in your AWS cluster can now communicate with a database running on-premise by simply connecting to its standard local Kubernetes DNS address (e.g., my-database.svc.cluster.local).
Skupper intercepts this local call and securely proxies the traffic over its encrypted network to the real service in the other cluster. From the application’s perspective, the remote service is running right next to it.
What Skupper is NOT
To understand Skupper’s value, it’s crucial to understand what it isn’t.
- It is not a Service Mesh: A service mesh like Istio is primarily focused on providing observability, security, and traffic management for services within a single cluster. Skupper is focused on the simpler problem of connecting services between clusters. They solve different problems but can be used together.
- It is not a VPN or CNI: Skupper operates at the application layer (Layer 7), not the network layer (Layer 3/4). It doesn’t care about IP addresses or network topologies. This is its key advantage, as it eliminates the need for complex network-level tunnels and firewall rules.
The Key Benefits of Using Skupper
- Radical Simplicity: Skupper replaces the need for specialized network engineering to configure complex VPNs with a simple command that any developer or DevOps engineer can run. It dramatically lowers the barrier to creating distributed applications.
- Secure by Default: All traffic sent over the Skupper network is automatically secured with mutual TLS (mTLS), providing end-to-end encryption without complex certificate management. By default, no services are exposed; you must explicitly opt-in, ensuring a secure posture.
- Hybrid and Multi-Cloud Native: Skupper is built for the reality of modern IT. It works identically across any Kubernetes distribution (OpenShift, EKS, AKS, GKE, K3s), allowing you to seamlessly connect services regardless of where they are running.
- Resilient and Performant: The network of Skupper routers can establish multiple paths between clusters. If one network link goes down, traffic can be automatically and transparently rerouted through an alternate path, increasing the resilience of your distributed application.
Conclusion
As applications become more geographically distributed, the need for a simple and secure way to connect them becomes paramount. Skupper provides an elegant, application-centric solution to the complex problem of multi-cluster communication. It abstracts away the underlying network chaos, allowing your distributed services to function as a single, cohesive unit. In doing so, it provides the virtual superhighway that truly enables the promise of hybrid and multi-cloud computing.
