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Metadata
ID:docker-best-practices/copy-reference-from
Language: Docker
Severity: Warning
Category: Best Practices
Description
This rule enforces that the COPY instruction must reference a valid build stage alias defined by a preceding FROM statement using the as keyword. Specifically, the --from flag in COPY should only point to an existing build stage alias, ensuring that the source files are correctly retrieved from the intended build context.
To avoid violations, always declare build stages with FROM <image> as <alias> before using COPY --from=<alias>. Verify that the alias used in COPY matches exactly with the alias declared in the earlier FROM statement. For example, using FROM debian:jesse as build followed by COPY --from=build ... ensures compliance and reliable builds.
Non-Compliant Code Examples
FROMdebian:jesseasbuildCOPY --from=build some stuff ./
Compliant Code Examples
FROMdebian:jesseasbuildRUN stuffFROMdebian:jesseCOPY --from=build some stuff ./
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rulesets:- docker-best-practices # Rules to enforce Docker best practices.
