Warning at multistage build about dockerfilelint HOT 6 CLOSED

Found this issue after discovering there's no multistage support.

For anyone that needs such a thing, consider the alternative linter hadolint.

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@SimonHeimberg I checked the Dockerfile posted by @AuthorProxy and the one I posted as an example in http://www.dockerfilelint.com and noticed that the line FROM base AS dependencies gives a warning because of the FROM <any_image>:<tag> is correctly using the image base but it doesn't have a tag associated to it.

dockerfilelint must be thinking that base is a published image and using the latest tag (assumed because the tag is not present) is not recommended.

The bug could be summarized into: When reusing stages with the FROM directive in a multistage Dockerfile, dockerfilelint gives a false positive warning for not having a tag associated to it.

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@darkvertex Thanks!. The multistage Dockerfile I used as an example before shows no warnings on the online version of hadolint.

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There are two online checkers using this tool:

• https://www.fromlatest.io/#/ , the original one, which is outdated
• http://www.dockerfilelint.com/#/ , which uses a newer version of this tool. It supports multistage dockerfiles

But the other problem:
Both ask for a tag for line 15 (FROM base AS dependencies), which does not make sense (at least probably) because base is defined in the dockerfile. This also happens on version 1.5.0 running locally. The alternative hadolint does not have this problem.

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@AmauryOrtega Thanks for this nice summary. I can confirm your findings.

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@AuthorProxy This warning appears because you don't specify the tag on the FROM statements.
An example for a multistage build that doesn't show those warnings:

FROM node:8.4.0-slim as clientbuilder
WORKDIR /app
COPY src/main/frontend .
RUN yarn
RUN npm run build

FROM openjdk:8u141-jdk-slim as serverbuilder
WORKDIR /app
COPY . .
COPY --from=clientbuilder /app/dist /app/src/main/resources/static
RUN ./gradlew build

FROM openjdk:8-jre-alpine
ENV artifact app-0.0.1.jar
WORKDIR /app
COPY --from=serverbuilder /app/build/libs/${artifact} /app
EXPOSE 8080
ENTRYPOINT ["sh", "-c"]
CMD ["java -jar ${artifact}"]

In this case, the warning that appears are:

• Line 8: First Command Must Be FROM (Possible Bug)
• Line 15: First Command Must Be FROM (Possible Bug)

This is expected since there is no multistage support.

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