Sidecar
In plain terms
A helper container that runs alongside a main app to add capabilities.
Going deeper
The sidecar pattern attaches a secondary process (for logging, proxying, or security) next to the main container, sharing its environment. It adds features without modifying the app itself.
Under the hood
Decouples cross-cutting concerns from app code but adds resource overhead and lifecycle coupling; central to service-mesh data planes.
Examples
Envoy proxy sidecar, log shippers (Fluentd), Istio, config reloaders.
Think of it like...
Like a motorcycle sidecar: it rides attached to the main bike, carrying extra gear without changing how the motorcycle itself works.