DNS policies play a critical role in managing and securing workload communication for cloud-native applications running on Kubernetes clusters. Two popular options for implementing DNS policies are Calico and Cilium. While both have their merits, Calico’s approach offers several distinct advantages over Cilium’s, particularly in terms of flexibility, scalability, and overall operational simplicity.
In this blog post, we’ll explore these differences and why Calico might be the better choice for your Kubernetes and container environment.
Out-of-Box Experience
When setting up DNS policies, the initial experience can greatly influence the adoption and ease of use of a solution. A seamless integration without complex configurations is often preferred by teams to avoid operational overhead.
Calico
Calico integrates seamlessly with the Kubernetes DNS service (whether it’s CoreDNS or kube-dns). It snoops on DNS traffic without requiring any modifications to how DNS queries are handled in the cluster. This means that Calico provides out-of-the-box DNS policies without the need for additional customizations, making it a straightforward solution for teams looking to implement DNS security quickly and effectively.
Cilium
On the other hand, Cilium uses a DNS proxy to intercept DNS requests and enforce network policies based on the domain names queried. While this method is effective, it adds complexity by introducing an additional component that needs to be configured and maintained. This proxy setup can become a single point of failure, requiring high availability (HA) configurations, which increase both the operational burden and the cost.
Avoidance of Single Point of Failure
Resilience is a critical factor in networking solutions, especially in environments where downtime can have significant impacts. Ensuring that no single component can disrupt service is a key design consideration.
Calico
Calico takes a decentralized approach by not using a DNS proxy, which means that DNS resolution remains unaffected even if some components fail. This design ensures that the cluster’s ability to perform DNS resolution is maintained, reducing the risk of downtime and improving overall reliability.
Cilium
Conversely, Cilium’s DNS proxy acts as a critical component within the cluster. If the proxy fails, it could disrupt DNS resolution and policy enforcement across the entire cluster. Since Cilium embeds the DNS proxy within the Cilium agent on each node, any issue with a Cilium node could impact DNS traffic for all workloads on that node, creating a potential single point of failure.
Scalability
As Kubernetes environments grow, the ability of a DNS policy implementation to scale efficiently becomes increasingly important. A solution that can handle increased load without degradation in performance is essential for maintaining a healthy cluster.
Calico
Calico’s decentralized approach allows it to scale more efficiently. By using external DNS resolvers and custom scripts, each component of the DNS policy implementation can scale independently according to its load. This flexibility can lead to better overall performance under heavy DNS query loads, making Calico an ideal choice for large-scale environments.
Cilium
Cilium, however, might face scalability challenges due to its reliance on the DNS proxy, which must handle all DNS queries within the cluster. As DNS query volumes increase, the proxy could become a bottleneck, limiting scalability and potentially impacting performance. Additionally, the need to monitor and maintain the DNS proxy adds to the operational complexity.
Granular Control and Visibility
For effective network management, having detailed insights and control over DNS traffic is crucial. The ability to monitor, log, and customize DNS behavior enhances security and troubleshooting capabilities.
Calico
Calico excels in this area by offering DNS logging out-of-the-box. This feature allows teams to configure detailed logging, monitoring, and even custom behavior based on DNS responses. The flexibility provided by Calico’s approach ensures that teams can have comprehensive visibility into DNS activities and tailor their DNS policies to meet specific needs.
Cilium
In contrast, Cilium also provides logs and monitoring, but its integrated DNS proxy might offer less flexibility in terms of detailed control and customization. For example, redirecting DNS traffic to a proxy for a network traffic visualization tool like Hubble requires layer 7 policy configurations, which adds complexity and reduces the ease of customization.
data plane Lock-in
The underlying technology stack of a DNS policy implementation can influence its compatibility and performance in different environments. Flexibility in this area ensures that the solution can adapt to various infrastructure requirements.
Calico
Calico’s DNS policy implementation is independent of eBPF, which can be an advantage in environments where eBPF is not available or preferred due to compatibility or performance concerns. This independence allows Calico to be more versatile and adaptable to various environments.
Cilium
On the other hand, Cilium relies heavily on eBPF for its functionality. While eBPF offers powerful capabilities, this dependency can be a limitation in certain environments where eBPF is not supported or where its use may cause performance issues.
Summary
|
Calico’s DNS Policy Implementation |
Cilium’s DNS Policy Implementation |
|
| DNS Proxy Usage | Does not use a DNS proxy; snoops DNS requests directly. | Uses an FQDN proxy to intercept DNS requests, which adds complexity. |
| Out-of-Box Experience | Integrates seamlessly with Kubernetes DNS (CoreDNS or kube-dns); no modifications needed. | Requires configuration of DNS proxy, adding complexity and potential points of failure. |
| Avoidance of Single Point of Failure | Does not impact DNS resolution if it fails. | DNS proxy failure can disrupt DNS resolution and policy enforcement cluster-wide. |
| Scalability | Decentralized approach; scales independently, better performance under heavy loads. | Scalability limited by DNS proxy capacity, adding operational complexity. |
| Granular Control and Visibility | Offers out-of-the-box DNS logging, detailed logging, monitoring, and custom behavior based on DNS responses. | Provides logs and monitoring but with less flexibility and requires additional layer 7 policy for detailed DNS logging. |
| data plane Lock-in | Independent of eBPF; compatible with environments where eBPF is not preferred. | Relies heavily on eBPF, which can be limiting in certain environments. |
| Summary | Offers flexibility, scalability, control, and resilience. | Simpler, faster to get started but with less flexibility and potential scalability limitations. |
Conclusion
Calico’s approach to DNS policy implementation offers significant advantages in terms of flexibility, scalability, control, and resilience. While Cilium provides a simpler and faster way to get started with DNS policies, its reliance on a DNS proxy introduces potential complexity and scalability limitations. For teams seeking a robust, scalable, and customizable DNS policy solution for their Kubernetes environments, Calico is the clear choice.
For more information, download the Calico and Cilium buyer’s guide.
