Fixing Common Issues in Dockerfile: Building and Running Problems

When working with Docker, it’s not uncommon to encounter issues during the build and run stages. Recently, I faced two specific problems in a Dockerfile setup that I believe are worth sharing, along with their solutions. These problems involved the placement of ARG directives and the use of ENTRYPOINT. Let’s dive into the details and solutions.

Problem 1: Building Issue

The Issue

In the current Dockerfile, the ARG PACKAGE=eventindexer directive is placed after the FROM golang:1.21.0 as builder line. This causes an issue when building the Docker image with the command:

docker build . -t taiko-mono

The builder stage correctly receives the PACKAGE=eventindexer argument, but the subsequent stage using alpine does not. This results in an error during the COPY command:

Step 13/14 : COPY --from=builder /taiko-mono/packages/$PACKAGE/bin/$PACKAGE /usr/local/bin/
COPY failed: stat taiko-mono/packages//bin/: file does not exist

The Solution

To resolve this, move the ARG PACKAGE=eventindexer directive to the first line of the Dockerfile. Additionally, add ARG PACKAGE in each stage that needs it. Here’s how you can modify the Dockerfile:

ARG PACKAGE=eventindexer

FROM golang:1.21.0 as builder
ARG PACKAGE
# [Other build instructions]

FROM alpine:latest
ARG PACKAGE
# [Other instructions]
COPY --from=builder /taiko-mono/packages/$PACKAGE/bin/$PACKAGE /usr/local/bin/

This ensures that the PACKAGE variable is available in all stages of the build process.

Problem 2: Running Issue

The Issue

The Dockerfile currently uses:

ENTRYPOINT ["$PACKAGE"]

According to the Dockerfile reference, this form (known as the “exec form”):

makes it possible to avoid shell string munging, and to invoke commands using a specific command shell. This means that normal shell processing, such as variable substitution, doesn’t happen.

As a result, using ENTRYPOINT like this leads to an error when running the container:

docker: Error response from daemon: failed to create task for container: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: exec: "${PACKAGE}": executable file not found in $PATH: unknown.

The Solution

To fix this, add an ENV directive to set the PACKAGE environment variable and change the ENTRYPOINT to use the fully qualified path. Here’s the updated Dockerfile snippet:

ENV PACKAGE=${PACKAGE}
ENTRYPOINT /usr/local/bin/${PACKAGE}

This ensures that the PACKAGE variable is correctly substituted and the executable is found in the specified path.

Conclusion

By addressing these two common issues—correctly placing ARG directives and properly using ENTRYPOINT—you can avoid build and run errors in your Docker setup. These adjustments ensure that all stages of your Docker build process receive the necessary arguments and that your container runs the intended executable without issues.

I hope this guide helps you troubleshoot similar problems in your Docker projects. Happy Dockerizing!