hadolint doesn't validate FROM instruction order in Dockerfile as it should #737
Description
- This is a bug report
- This is a feature request
- I searched existing issues before opening this one
Expected behavior
The FROM instruction initializes a new build stage and sets the Base Image for subsequent instructions. As such, a valid Dockerfile must start with a FROM instruction (with the only exceptions of comment lines or ARG).
https://docs.docker.com/engine/reference/builder/#from
However, currently hadolint doesn't check for that instruction sequence, which is a breaking failure error for docker build if this FROM precedence rule isn't followed.
Actual behavior
halolint should error out on any Dockerfile that doesn't start with comments / ARG lines. It doesn't as of version 2.8.0.
Steps to reproduce the behavior
Output of hadolint --version or
docker run --rm hadolint/hadolint hadolint --version or
docker run --rm ghcr.io/hadolint/hadolint hadolint --version:
It looks like the Homebrew installed hadolint doesn't properly display a version, another bug for the recipes.
$ hadolint --version
Haskell Dockerfile Linter UNKNOWN
$ brew info hadolint
hadolint: stable 2.8.0 (bottled)
Smarter Dockerfile linter to validate best practices
https://github.com/hadolint/hadolint
/opt/homebrew/Cellar/hadolint/2.8.0 (5 files, 82MB) *
Poured from bottle on 2021-11-22 at 17:24:54
From: https://github.com/Homebrew/homebrew-core/blob/HEAD/Formula/hadolint.rb
License: GPL-3.0-only
$ cat <<EOF | hadolint -
LABEL maintainer="ye@example.com"
FROM python:3.9-slim-bullseye
ARG DEBIAN_FRONTEND=noninteractive
EOF
$ echo $?
0
cat <<EOF | docker build -f - .
LABEL maintainer="ye@example.com"
FROM python:3.9-slim-bullseye
ARG DEBIAN_FRONTEND=noninteractive
EOF
[+] Building 0.5s (2/2) FINISHED
=> [internal] load build definition from Dockerfile 0.3s
=> => transferring dockerfile: 144B 0.0s
=> ERROR [internal] load .dockerignore 0.2s
=> => transferring context: 40B 0.1s
------
> [internal] load .dockerignore:
------
failed to solve with frontend dockerfile.v0: failed to create LLB definition: no build stage in current contextDockerfile (if relevant)
BAD Dockerfile
LABEL maintainer="ye@example.com"
FROM python:3.9.7-slim-bullseye
ARG DEBIAN_FRONTEND=noninteractiveGOOD Dockerfile
FROM python:3.9.7-slim-bullseye
LABEL maintainer="ye@example.com"
ARG DEBIAN_FRONTEND=noninteractiveAdditional environment details (OS, stack version, etc.)
Switching the instruction lines between LABEL and FROM will make docker build work.