Exemplo de arquivo Dockerfile para projetos Rails somente API usando Alpine e com banco de dados SQLite

docker-compose.yml

version: '3.7'

services:
  web:
    build: .
    ports:
      - ${WEB_PORT:-3000}:3000
    volumes:
      - public:/app/public
      - .:/app
    stdin_open: true
    tty: true

volumes:
  public:
    driver: local

Dockerfile

FROM ruby:3.2.2-alpine
LABEL maintainer="Lucivaldo Castro <lucivaldocb@gmail.com>"

RUN apk update && apk add --virtual build-dependencies build-base

RUN apk add \
  less \
  mailcap \
  sqlite-dev \
  tzdata

# Set timezone env
ENV TZ America/Araguaina

# Set Timezone
RUN cp /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone

# Set locale
ENV LANG pt_BR.UTF-8
ENV LANGUAGE pt_BR.UTF-8
ENV LC_ALL pt_BR.UTF-8

RUN mkdir /app
WORKDIR /app

COPY Gemfile .
COPY Gemfile.lock .
RUN bundle install

COPY . /app

CMD ["./start.sh"]

RUN apk del build-dependencies

start.sh

#!/bin/sh

rm -rf /app/tmp/pids/server.pid
bundle exec rails server -b 0.0.0.0