Choosing a Container Network Interface (CNI) for Kubernetes used to be a simple decision. Does it connect pods? Good enough. Today, that choice is a foundational platform decision that dictates your cluster's security posture, performance limits, and observability capabilities for years to come. Your CNI is no longer just a networking plugin; it's a critical piece of infrastructure that can either accelerate or bottleneck your entire stack.
In 2026, the conversation is dominated by two leaders: Cilium and Calico. Both are powerful, mature, and trusted in massive production environments. But they represent different philosophies and technical approaches. Calico offers battle-tested flexibility with a rich history, while Cilium represents a new, eBPF-native world of networking. This guide will cut through the noise to help your platform team make the right long-term decision, focusing not just on features, but on the strategic implications for performance, security, and operations at scale.
The Core Differentiator: The Rise of eBPF
To understand the Cilium vs. Calico debate, you first have to understand eBPF (extended Berkeley Packet Filter). Think of eBPF as a way to run sandboxed, event-driven programs directly within the Linux kernel without changing kernel source code. For networking, this is a game-changer. You can find a deep dive on the technology at the official eBPF & Cilium community site.
For decades, Kubernetes networking relied on iptables or IPVS. These tools are powerful but operate by creating long, complex chains of rules. As your cluster grows, with thousands of services and pods, traversing these chains for every single packet adds significant CPU overhead and latency. It's like sending a package through a city with thousands of traffic stops.
eBPF offers a direct path. eBPF programs can be attached to network interfaces to make intelligent routing and filtering decisions right at the source, bypassing the cumbersome iptables and conntrack subsystems entirely. The result is a faster, more efficient, and more programmable data path.
- Cilium was built from the ground up with eBPF as its core. Every feature (networking, observability, and security) is designed to leverage the power and efficiency of eBPF.
-
Calico started with a standard Linux networking data plane using
iptablesand IP-in-IP or BGP for routing. It's incredibly robust and well-understood. Recognizing the power of eBPF, Calico introduced a pluggable eBPF data plane. This gives you a choice, but it also means eBPF is an add-on to its core architecture rather than its native foundation.
This fundamental difference in architecture is the source of nearly every other distinction between the two projects.
Network Policy and Security Showdown
Both Cilium and Calico provide robust network security, but their approaches and advanced capabilities differ significantly due to eBPF.
Calico's Policy Engine
Calico has long been the gold standard for network policy. It supports standard Kubernetes NetworkPolicy resources and extends them with its own CRDs like GlobalNetworkPolicy and NetworkPolicy with richer features like explicit deny rules and rule ordering.
A typical Calico policy is direct and focuses on L3/L4 (IP and port) filtering. Here's an example that allows ingress from pods with the app: frontend label to port 6379/TCP on pods with the app: database label.
apiVersion: projectcalico.org/v3
kind: NetworkPolicy
metadata:
name: allow-frontend-to-db
namespace: production
spec:
selector: app == 'database'
types:
- Ingress
ingress:
- action: Allow
protocol: TCP
source:
selector: app == 'frontend'
destination:
ports:
- 6379
This is clear, effective, and works reliably across Calico's standard and eBPF data planes. For many organizations, this level of control is perfectly sufficient.
Cilium's L7-Aware Security
Cilium's eBPF-native approach allows it to operate at a much higher level of the stack. It can parse application-layer protocols like HTTP, gRPC, and Kafka directly from the kernel. This enables incredibly granular, identity-aware policies that iptables-based systems simply cannot match.
Imagine you want to allow the billing-service to read from a metrics-api but not write to it. With Cilium, you can enforce this at the API level.
apiVersion: "cilium.io/v2"
kind: CiliumNetworkPolicy
metadata:
name: api-aware-policy-example
namespace: production
spec:
endpointSelector:
matchLabels:
app: metrics-api
ingress:
- fromEndpoints:
- matchLabels:
app: billing-service
toPorts:
- ports:
- port: "8080"
protocol: TCP
rules:
http:
- method: "GET"
path: "/api/v1/metrics"
This policy enforces that only GET requests to /api/v1/metrics are allowed from the billing-service. Any POST, DELETE, or other requests would be dropped by the CNI, even if they are on the correct port. This is a massive security enhancement, effectively turning your network into a zero-trust environment at the API level without requiring a service mesh.
For encryption, both projects support WireGuard for transparent, in-transit encryption between nodes, providing a modern and performant alternative to IPsec.
Performance and Scalability in 2026
In a small cluster, the performance difference between Cilium and Calico's eBPF mode might be negligible. But when you scale to hundreds of nodes and tens of thousands of pods, the architectural differences become stark.
The primary performance advantage of eBPF comes from avoiding the iptables and conntrack kernel subsystems.
-
Reduced CPU Overhead: Every packet doesn't need to traverse long chains of
iptablesrules. This frees up significant CPU cycles on each node, which can then be used by your applications. This is especially noticeable on nodes with high connection churn. - Lower Latency: By processing packets on a more direct path, eBPF reduces the per-packet latency within the cluster. This can have a meaningful impact on the performance of latency-sensitive applications like databases or real-time APIs.
- Improved Throughput: The efficiency of the eBPF data path allows for higher overall network throughput, a key consideration for data-intensive workloads.
While Calico's eBPF mode also gains these benefits, Cilium's eBPF implementation is often considered more mature and deeply integrated, having been the project's sole focus since its inception. In large-scale clusters, this maturity can translate to better stability and more predictable performance under extreme load. If you are deploying large clusters, for example when you deploy an EKS cluster with Terraform, this long-term performance profile becomes a critical factor.
Observability: Seeing the Unseen
Troubleshooting network issues in Kubernetes can be a nightmare. Is a packet being dropped by a network policy? Is a service not responding? This is where built-in observability tools make a huge difference.
Cilium's Hubble
Cilium comes with Hubble, a powerful, purpose-built observability platform that leverages eBPF to provide deep visibility into network flows without any application instrumentation. It gives you a service dependency map, real-time flow data, and policy troubleshooting tools out of the box.
With the Hubble CLI, you can immediately see what's happening. For instance, to see all DNS requests and replies in real time:
$ # Assuming Cilium v1.15+ and Hubble is enabled
$ hubble observe --protocol dns -f
TIMESTAMP SOURCE DESTINATION TYPE VERDICT SUMMARY
May 20 12:34:56.123Z kube-system/coredns-abcde default/my-app-fghij L7:response FORWARDED DNS Qry: A, Rcode: NOERROR
May 20 12:34:56.456Z default/my-app-fghij kube-system/coredns-abcde L7:request FORWARDED DNS Qry: my-external-service.com.
The Hubble UI provides a graphical representation of this data, making it incredibly easy to spot anomalies or understand service communication patterns. If you're constantly fighting weird networking bugs or dealing with a CrashLoopBackOff, this level of insight can save hours of debugging.
Calico's Observability
Calico Enterprise offers similar observability features, including a dynamic service graph and flow visualization. In the open-source version, observability is typically achieved by exporting metrics to Prometheus and building Grafana dashboards. This is a powerful and flexible approach, but it requires more setup and integration effort. You can get flow logs, but they are not as rich or easily queryable as what Hubble provides out of the box.
For teams that want a "batteries-included" observability solution tightly coupled with their CNI, Hubble is a clear winner. For teams that prefer to build their own observability stack around standards like Prometheus, Calico's approach is perfectly viable.
The Blurring Lines with Service Mesh
The next battleground for CNIs is the service mesh. Both Cilium and Calico are expanding their feature sets to provide capabilities traditionally associated with tools like Istio or Linkerd.
- Cilium Service Mesh: Cilium offers service mesh features like traffic management (retries, timeouts), canary deployments, and mTLS encryption without requiring a sidecar proxy. It achieves this by embedding Envoy proxy functionality directly into the CNI layer, managed by eBPF. This sidecar-less model promises better performance and lower resource overhead compared to traditional service meshes.
- Calico and Istio: Calico's strategy is to provide best-in-class integration with Istio. It can accelerate Istio's data plane by offloading some of the networking functions to its eBPF layer. This allows you to combine Calico's robust CNI and policy engine with the full, mature feature set of the Istio service mesh.
This presents a strategic choice: do you want a single, integrated platform for networking, security, and service mesh (Cilium), or do you prefer a modular approach, combining a dedicated CNI (Calico) with a dedicated service mesh (Istio)?
Making the Choice: A Decision Framework
There is no single "best" CNI. The right choice depends entirely on your team's priorities, existing infrastructure, and future goals.
Choose Cilium if
- Performance is your top priority. You run latency-sensitive or high-throughput applications and want to squeeze every ounce of performance from your infrastructure.
- You need advanced, L7-aware security. Your security model requires enforcing policies at the API level (HTTP, gRPC) and you want to build a zero-trust network.
- You want built-in, out-of-the-box observability. Your team values integrated tools like Hubble for rapid troubleshooting and dependency mapping.
- You are building a new platform and are "all-in" on eBPF. You are comfortable adopting a modern, eBPF-native stack and are interested in its integrated service mesh capabilities.
Choose Calico if
- You need maximum flexibility and a proven track record. You operate in diverse environments (on-prem, multiple clouds) and need a CNI that supports various data planes (standard Linux, eBPF, Windows).
- Your organization already has a significant investment in Istio. Calico's deep integration with Istio allows you to enhance your existing service mesh with a powerful CNI.
- You prefer a more gradual adoption of eBPF. You want the option to run some clusters with the well-understood standard Linux data plane while experimenting with the eBPF data plane in others.
- Your team has deep expertise in traditional Linux networking. Calico's architecture will feel familiar and its use of BGP for routing is a standard in many enterprises.
Frequently Asked Questions (FAQ)
1. Is eBPF mature enough for production in 2026?
Absolutely. eBPF has been a stable part of the Linux kernel for years. It's used in production by massive tech companies like Google, Meta, and Netflix to handle networking, security, and observability at an immense scale. Both Cilium and Calico's eBPF implementations are considered production-grade.
2. Can I migrate from Calico to another CNI like Cilium?
Yes, but it's a complex and disruptive process. A CNI migration typically requires a "rip and replace" approach, which involves draining nodes, uninstalling the old CNI, installing the new one, and then uncordoning the nodes. This requires careful planning and significant downtime. It's far better to make the right choice from the beginning.
3. Does Calico's standard Linux data plane still have a place?
Yes. For environments with older Linux kernels that lack the necessary eBPF features, or for teams who prioritize stability and familiarity over cutting-edge performance, the standard iptables-based data plane is still a very solid and reliable choice. It's one of Calico's key strengths: providing that flexibility.
4. What about other CNIs like Flannel or Weave Net?
While Flannel and Weave Net are excellent for getting started or for smaller, less demanding clusters, they generally lack the advanced security, observability, and performance features of Cilium and Calico. For any serious production platform, the choice has largely narrowed to these two.
Conclusion
Choosing between Cilium and Calico is a strategic decision that will shape your Kubernetes platform for years. It's a choice between an eBPF-native, all-in-one solution that pushes the boundaries of performance and security (Cilium), and a flexible, battle-hardened CNI that offers a choice of data planes and deep integration with the wider ecosystem (Calico).
Your next step should be hands-on evaluation. Don't just read about it. Spin up two identical test clusters. Install Cilium on one and Calico with the eBPF data plane on the other. Deploy a sample application and use tools like netperf to measure throughput and latency. Test a complex network policy on each. Use Hubble to visualize traffic. Only by seeing how they operate in your environment can you make a truly informed decision for the future of your platform.
