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In Kubernetes, pods often need to securely communicate with external resources, such as internet services or APIs. Traditional Kubernetes network policies use IP addresses to identify these external resources. However, managing policies with IP addresses can be challenging because IPs often change, especially when dealing with dynamic websites or APIs.
Calico Enterprise addresses this challenge by extending Kubernetes network policies to support Fully Qualified Domain Names (FQDNs). This allows users to define policies using domain names instead of IP addresses, making it easier to manage and secure egress traffic. By dynamically mapping domain names to IPs, Calico ensures that policies remain up-to-date, enabling seamless and secure connectivity to external resources.
While this approach is conceptually simple, practical implementation is tricky. DNS mappings are dynamic: domain names often resolve to different IPs with each query, and wildcard support (e.g., *.example.com) adds complexity. To address this, Calico monitors DNS traffic to create and manage domain-to-IP mappings dynamically, translating high-level DNS-based rules into efficient low-level constructs like iptables, nftables, or eBPF.
Evolution of Calico DNS policy implementation
The DNS policy implementation significantly impacts performance and reliability. Currently, Calico offers three different modes to operate the DNS Continue reading