Devcontainer Build without cache hangs after mostly successful build

[ontoneio]

So I am running into a weird issue with my devcontainer environment. I am building without the cache inside a Vscode IDE and the image build seems to get to the very last step and then throws this warning and does not ever resolve the build into the devcontainer environment.

 1 warning found (use docker --debug to expand):
 - InvalidDefaultArgInFrom: Default value for ARG $BASE_IMAGE results in empty or invalid base image name (line 2)
[303440 ms] Start: Run: docker events --format {{json .}} --filter event=start
[303442 ms] Start: Starting container

I personally do not have a BASE_IMAGE Argument present in my docker image, so I am not understanding why my build would be failing to propagate due to a variable I don't use?

For debugging sake I even tried adding these lines and still get the error from above...

ARG BASE_IMAGE=mcr.microsoft.com/vscode/devcontainers/base:ubuntu-24.04
FROM ${BASE_IMAGE} AS base

Why would I be getting this error?

[ontoneio]

@samruddhikhandale OR @chrmarti have either of you seen this before?

I have even put this docker check directive in my Dockerfile and it still pauses the build without resolution.

# syntax=docker/dockerfile:1
# check=skip=InvalidDefaultArgInFrom

[sireeshajonnalagadda]

Hi @ontoneio,

Thank you for reporting this issue!

This warning is likely coming from devcontainers/cli’s internal build logic, not from your project’s Dockerfile.

The repo contains an internal Dockerfile fragment like:

Dockerfile
ARG BASE_IMAGE
FROM $BASE_IMAGE
This can trigger BuildKit’s InvalidDefaultArgInFrom warning because the FROM instruction depends on an ARG with no inline default at parse time.

So, seeing a BASE_IMAGE warning does not necessarily mean your project’s Dockerfile defines BASE_IMAGE.

Also, this warning may not be the root cause of the failure — the log suggests the hang happens later, during container startup (Start: Starting container).

If possible, could you please share your Dockerfile so I can try to reproduce the issue? I’ll investigate further once I have that information.

Thank you,
Sireesha

[ontoneio]

Hello @sireeshajonnalagadda

Thanks for the response. I will share my Dockerfile with some info redacted.

# syntax=docker/dockerfile:1
# check=skip=InvalidDefaultArgInFrom

# ----------------------------------------------------------
# VS-Code Development Docker Image
# ----------------------------------------------------------
#
# ARG BASE_IMAGE=mcr.microsoft.com/devcontainers/base:noble
FROM mcr.microsoft.com/devcontainers/base:noble AS base

# BASE ARGS
ARG INSTALL_ZSH="false"
ARG UPGRADE_PACKAGES="true"
ARG USE_MOBY="true"
ARG USERNAME=vscode
ARG USER_UID=1000
ARG USER_GID=$USER_UID
# BASE ENV
ENV HOME=/home/${USERNAME}
# Enable new "BUILDKIT" mode for Docker CLI
ENV DOCKER_BUILDKIT=1

RUN mkdir -p ${HOME}/.vscode-server/extensions && \
    chown -R ${USERNAME} ${HOME}/.vscode-server

FROM base AS op_system

SHELL [ "/bin/bash", "-c" ]
# since we're starting non-interactive shell,
# we wil need to tell bash to load .bashrc manually
ENV BASH_ENV=~/.bashrc

RUN groupadd docker && \
    usermod -aG docker ${USERNAME}

# PACKAGING
FROM op_system AS packaging

ARG BUILD_DATE
ARG RELEASE_VERSION

LABEL org.opencontainers.image.created=${BUILD_DATE}
LABEL org.opencontainers.image.version=${RELEASE_VERSION}
LABEL org.opencontainers.image.description="Image housing all build/development tooling for Magnolia CMS development"

I am not sure if my scripts are the reason this fails, it seems like everything from my devcontainer.json worked just fine.
The container build seemed to succeed, but I had to open it manually and a new VSCode window instead of just being after the build inside the same window.

[sireeshajonnalagadda]

Hi @ontoneio,

I was able to reproduce and validate the warning path locally. The warning appeared, but the build completed successfully. Could you confirm whether this is breaking your code or causing build failures on your side?

Findings

The InvalidDefaultArgInFrom warning originates from internal Dev Containers CLI Dockerfile flows, not from the user Dockerfile.

Specifically, the internal UID-update Dockerfile had an ARG used by FROM without an inline default, which triggered BuildKit linting.

Changes Made Locally

Added a default for BASE_IMAGE in updateUID.Dockerfile.

Updated feature-generated Dockerfile flows to use a safe default pattern in:

containerFeaturesConfiguration.ts

containerFeatures.ts

Why This Helps

BuildKit no longer encounters an empty/invalid default at parse time for ARG values consumed by FROM.

This eliminates the warning noise and avoids confusion that it originated from the user Dockerfile.

Validation

Built and ran the local CLI from source.

Re-ran devcontainer up with --no-cache against the example config.

Container startup completed successfully in local verification.

I am yet to run some more checks and tests, please allow me some time, I will get back to you.

Thanks,
Sireesha

[ontoneio]

@sireeshajonnalagadda
It's not a breaking issue. It breaks the build, but weirdly is able to build the container image fine, but it makes you open it manually through VScode instead of being opened automatically as it used to. So you need two separate windows for the same code base but different environments if that makes sense. So definitely a weird bug from my viewpoint.