ResourceFieldRef

ResourceFieldRef is a component of the Kubernetes Downward API that enables a container to expose its resource values, such as CPU and memory requests or limits, to the Pod at runtime. It allows these resource quantities to be injected into environment variables or consumed by downward API projections, facilitating dynamic configuration based on the container’s defined resources.

Usage and structure: ResourceFieldRef is used in the Pod specification where a container defines environment variables with a valueFrom/resourceFieldRef reference. The relevant fields typically include an optional containerName (when referencing resources from another container in the same Pod), resource (for example, requests.cpu, limits.memory, etc.), and an optional divisor to scale the returned value. The value produced is a string representing the specified resource quantity, possibly adjusted by the divisor. In practice, common usage is to expose a container’s CPU or memory requests or limits as an environment variable.

Supported resources and behavior: The resource field generally supports the standard container resource names such as requests.cpu, limits.cpu, requests.memory, and limits.memory. The divisor is an optional scaling factor that can alter the unit or magnitude of the reported value. The value reflects the resource specification defined in the Pod (not the container’s runtime usage) and remains static for the life of the Pod unless the Pod spec is changed.

Limitations and notes: ResourceFieldRef is part of the downward API and is primarily intended for configuration and instrumentation, not real-time usage tracking. It is commonly used to adapt application behavior to the resources allocated to the container.

See also: Downward API, FieldRef, Resource requirements.