Kubernetes Informers are so easy... to misuse!

Kubernetes Informers, integral to managing the reconciliation process in Kubernetes clusters, can be both powerful and challenging to use, particularly in large-scale environments. Render, a cloud infrastructure company, recently shared insights from their experience with Informers while tracking data on their Kubernetes clusters to measure compute efficiency. The post highlights the potential pitfalls of Informers, such as the risk of relying on edge-driven logic instead of the recommended level-driven approach, which can lead to missed state transitions and issues during production rollouts. Additionally, they warn about the "OOMLoop," where inefficient handling of events can lead to excessive memory usage and crashes. To mitigate these challenges, Render suggests using Informer's in-memory cache, employing label selectors with SharedInformerFactory to limit resource updates, and using SetTransform to manage memory usage effectively. The article emphasizes the need for careful design and understanding of Informers' architecture to avoid common problems and improve controller performance at scale.