How to Rollout an Update for a CNI Without Breaking the World Wide Web

Introduction

Container Network Interface (CNI) is a critical component in modern containerized environments, enabling seamless network communication between containers. As cloud-native technologies evolve, the need for robust, flexible, and reliable CNI solutions becomes increasingly important. This article explores how to safely update a CNI implementation, such as Calico, while minimizing risks to the broader ecosystem, including the global internet.

Calico Overview

Calico is an open-source network and security solution designed for cloud, Kubernetes, bare metal, and virtualized environments. It provides a unified networking layer across all environments, supporting multiple data planes including eBPF, IPTables, Windows HNS, and VPP. Its enterprise-grade security and scalability make it a preferred choice for organizations like NASA, Reddit, and Walmart.

Feature Flags in CNI Management

Feature flags are a vital mechanism for managing CNI updates. They allow for controlled deployment of new features without disrupting existing services. Key applications include:

• Feature Toggle Mechanism: Variables control application behavior, enabling feature activation or deactivation without restarting services.
• Data Plane Plugin Switching: Flags determine which data plane (e.g., VPP) is used, allowing for seamless transitions between different network implementations.
• Experimental Feature Testing: New features can be tested in production environments, reducing the risk of unintended consequences.
• Flag Providers: Support for JSON/YAML/database formats or standardized solutions like Open Feature ensures flexibility in managing flags.

Case Study: Reddit Upgrade Incident

A recent upgrade from Kubernetes 1.123 to 1.124 caused a critical outage for Reddit. The root cause was the removal of the master label from control plane nodes in Kubernetes 1.124. Calico relied on this label to detect BGP devices, leading to a failure in establishing BGP connections. The lack of automatic label detection exacerbated the issue, resulting in network disruptions.

Post-Upgrade Improvements:

• Introduced Calico API Server and Tigera Operator to streamline upgrade processes.
• Enhanced documentation to emphasize label configuration and BGP setup accuracy.
• Provided CubeCTL as an alternative to deprecated commands, improving operational efficiency.

Key Technical Considerations

• BGP Configuration: Managed via bird tool, dependent on the bgp flag to initiate BGP processes.
• Label Dependency: Calico depends on master labels to identify BGP devices on control plane nodes.
• Upgrade Risks: Inadequate documentation review or testing can lead to environment compatibility issues.
• Mitigation Strategies: Strict adherence to documentation, pre-upgrade testing, and verification of flag configurations are essential.

Conclusion

Updating a CNI like Calico requires meticulous attention to documentation, flag configurations, and environment compatibility. By leveraging feature flags, organizations can safely test and deploy changes without compromising the stability of the global internet. Always prioritize thorough testing and documentation review before implementing updates to avoid widespread disruptions.