How to Fix Docker Build Failure in Rails

A Docker Build Failure in Rails usually signals a straightforward configuration problem. Here's exactly how to fix it.

Understanding the Problem

Docker build failures in Rails usually come from missing system dependencies, incorrect base images, or build steps that require files not yet copied into the container. The minimal container environment differs significantly from your local machine.

Solution

The key is to install native extensions in the build stage and use a slim image for production:

FROM ruby:3.2-slim AS build
RUN apt-get update && apt-get install -y build-essential libpq-dev
WORKDIR /app
COPY Gemfile Gemfile.lock ./
RUN bundle install --without development test
COPY . .
RUN SECRET_KEY_BASE=dummy rails assets:precompile

FROM ruby:3.2-slim
RUN apt-get update && apt-get install -y libpq5 && rm -rf /var/lib/apt/lists/*
WORKDIR /app
COPY --from=build /app .
CMD ["rails", "server", "-b", "0.0.0.0"]

Common Pitfall

Don't overlook your CI/CD pipeline — sometimes the fix works locally but the deployment environment has different defaults. Make sure your Rails configuration is explicit rather than relying on defaults. Review your Rails project's dependency tree after applying this fix. Outdated packages are a common source of subtle incompatibilities.

Confirming It Works

To confirm the fix is working, check your Rails application logs for any remaining error traces. You should see clean request/response cycles without the previous error. Deploy to a staging environment to verify the fix holds under production-like conditions.

Going Forward

Consider integrating [Bugsly](https://bugsly.dev) into your Rails workflow to catch, track, and resolve errors like this automatically.