valueFromresourceFieldRef

valueFromresourceFieldRef is a feature in Kubernetes Pod specifications that allows an environment variable to be populated from a resource field reference. It is used within a container’s environment variable definition, under valueFrom and resourceFieldRef, to expose resource-related values of a container in the same pod.

Syntax and fields

- containerName (optional): the name of the target container in the pod whose resources are being referenced. If omitted, the resources of the current container (the one defining the env var) are used.

- resource (required): the specific resource field to reference. Typical values include requests.cpu, limits.cpu, requests.memory, limits.memory, requests.ephemeral-storage, and limits.ephemeral-storage.

Behavior and interpretation

The referenced resource value is injected as a string into the environment variable at runtime. CPU values use the standard Kubernetes quantity format (for example 1000m for 1 CPU, or 0.5 as 0.5 cores). Memory and ephemeral storage are represented using their quantity units (for example 524288Ki for bytes with a unit suffix). The result is a string that downstream processes can parse as needed.

Examples

- An environment variable that captures the CPU limit for a container named web:

name: CPU_LIMIT

valueFrom:

resourceFieldRef:

containerName: web

resource: limits.cpu

- An environment variable that captures memory requests for the current container:

name: MEM_REQUEST

valueFrom:

resourceFieldRef:

resource: requests.memory

Notes

valueFromresourceFieldRef is a form of the Pod’s Downward API that enables dynamic configuration based on container resource specifications. It is particularly useful for debugging, logging, or configuring applications that adapt to their resource constraints.