Dockerfile ARG not being properly set in FROM

January 23, 2023

In my Dockerfile I have a typical setup for an image tag but I’m trying to make a multi-stage build:

FROM docker.io/library/alpine as first-stage

RUN echo "test"

ARG VERSION="latest"

FROM docker.io/library/hello-world:${VERSION} as second-stage

but when I try to build it with a command like:

docker build \
    --tag=img-name-dev:latest \
    .

(running from the directory that the Dockerfile lives in)

I get in my real code:

failed to solve with frontend dockerfile.v0: failed to create LLB definition: failed to parse stage name "link.to.my/image:": invalid reference format

or in the minimal reproducible example:

Step 4/4 : FROM docker.io/library/hello-world:${VERSION} as second-stage
invalid reference format

which indicates to me that the VERSION is empty, rather than being filled with latest. If I remove the ${VERSION} and replace it simply with latest it works (so it’s not a permissions issue pulling the image).

What am I doing wrong?

Docker version:

Client: Docker Engine - Community
 Version:           20.10.23
 API version:       1.41
 Go version:        go1.18.10
 Git commit:        7155243
 Built:             Thu Jan 19 17:34:12 2023
 OS/Arch:           linux/amd64
 Context:           default
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          20.10.23
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.18.10
  Git commit:       6051f14
  Built:            Thu Jan 19 17:32:03 2023
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.15
  GitCommit:        5b842e528e99d4d4c1686467debf2bd4b88ecd86
 runc:
  Version:          1.1.4
  GitCommit:        v1.1.4-0-g5fd4c4d
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Docker Compose version v2.13.0

>Solution :

Any ARG that is used within a FROM command must occur before the first FROM statement. So move your ARG to the very top of your file — above the additional first stage that you mentioned in the comments. See the Dockerfile reference.