Using Fullstaq Ruby on Heroku

app.json

{
    "stack": "container",
    "formation": {
        "web": {
            "quantity": 1,
            "size": "free"
        }
    },
    "addons": [{
            "plan": "heroku-postgresql:hobby-dev",
            "as": "DATABASE"
        },
        {
            "plan": "heroku-redis:hobby-dev",
            "as": "REDIS"
        }
    ],
    "env": {
        "SECRET_KEY_BASE": {
            "required": true,
            "generator": "secret"
        }
    }
}

Dockerfile.prod

# base dockerfile from https://github.com/evilmartians/terraforming-rails/blob/567566348a6a9893e10b9f857f1e5e58ba581b41/examples/dockerdev/.dockerdev/Dockerfile

# See explanation below
ARG RUBY_VERSION

FROM quay.io/evl.ms/fullstaq-ruby:$RUBY_VERSION-jemalloc-buster-slim as builder

ARG PG_MAJOR
ARG NODE_MAJOR
ARG BUNDLER_VERSION
ARG YARN_VERSION
ARG SECRET_KEY_BASE

# Common dependencies
RUN apt-get update -qq \
  && DEBIAN_FRONTEND=noninteractive apt-get install -yq --no-install-recommends \
    build-essential \
    zlib1g-dev \
    liblzma-dev \
    gnupg2 \
    curl \
    less \
    git \
  && apt-get clean \
  && rm -rf /var/cache/apt/archives/* \
  && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* \
  && truncate -s 0 /var/log/*log

# Add PostgreSQL to sources list
RUN curl -sSL https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add - \
  && echo 'deb http://apt.postgresql.org/pub/repos/apt/ buster-pgdg main' $PG_MAJOR > /etc/apt/sources.list.d/pgdg.list

# Add NodeJS to sources list
RUN curl -sL https://deb.nodesource.com/setup_$NODE_MAJOR.x | bash -

# Add Yarn to the sources list
RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - \
  && echo 'deb http://dl.yarnpkg.com/debian/ stable main' > /etc/apt/sources.list.d/yarn.list

# Application dependencies
# We use an external Aptfile for that, stay tuned
RUN apt-get update -qq && DEBIAN_FRONTEND=noninteractive apt-get -yq dist-upgrade && \
  DEBIAN_FRONTEND=noninteractive apt-get install -yq --no-install-recommends \
    libpq-dev \
    postgresql-client-$PG_MAJOR \
    nodejs \
    yarn=$YARN_VERSION-1 \
    $(cat /tmp/Aptfile | xargs) &&\
    apt-get clean && \
    rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* && \
    truncate -s 0 /var/log/*log

# Configure bundler
ENV LANG=C.UTF-8 \
  BUNDLE_JOBS=4 \
  BUNDLE_RETRY=3

ENV RAILS_ENV=production
ENV NODE_ENV=production
ENV SECRET_KEY_BASE=$SECRET_KEY_BASE
# Uncomment this line if you store Bundler settings in the project's root
# ENV BUNDLE_APP_CONFIG=.bundle

# Uncomment this line if you want to run binstubs without prefixing with `bin/` or `bundle exec`
# ENV PATH /app/bin:$PATH

# Upgrade RubyGems and install required Bundler version
RUN gem update --system && \
    gem install bundler:$BUNDLER_VERSION

# Create a directory for the app code
RUN mkdir -p /app

WORKDIR /app

COPY Gemfile Gemfile.lock ./

RUN bundle install --without development test

COPY . .

RUN bundle exec rails assets:precompile \
 && yarn cache clean \
 && rm -rf node_modules tmp/cache

CMD [ "bundle", "exec", "puma", "-C", "config/puma.rb" ]

heroku.yml

setup:
  addons:
    - plan: heroku-postgresql
      as: DATABASE
    - plan: heroku-redis
      as: REDIS
build:
  docker:
    web: Dockerfile.prod
  config:
    RUBY_VERSION: '2.7.1'
    PG_MAJOR: '12'
    NODE_MAJOR: '12'
    YARN_VERSION: '1.22.4'
    BUNDLER_VERSION: '2.1.4'
    SECRET_KEY_BASE: $SECRET_KEY_BASE