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ruby-deploy

DevOps & Security
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Build and deploy Ruby applications — Bundler, Rails, Rack, asset pipeline, bootsnap, and Dockerfile patterns. Use when deploying a Ruby or Rails project, or when a Gemfile is detected.

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Ruby Deployment

Detection

Project is Ruby if Gemfile exists at the root.

Versions

Ruby version priority:

  1. .ruby-version file
  2. Gemfile → ruby directive
  3. mise.toml or .tool-versions
  4. Defaults to 3.4

Package Manager

Bundler. Detect Gemfile and Gemfile.lock.

Bundler Version

Read from BUNDLED WITH in Gemfile.lock. Install: gem install bundler -v <version>.

Install Commands

ContextCommand
Productionbundle config set --local without 'development test' then bundle install
With lockfilebundle install --frozen
Without lockfilebundle install

Runtime Variables

BUNDLE_GEMFILE=/app/Gemfile
GEM_PATH=/usr/local/bundle
GEM_HOME=/usr/local/bundle
MALLOC_ARENA_MAX=2

Build & Start

Start Command Resolution

  1. Framework-specific (see below)
  2. config/environment.rb → load and run
  3. config.ru → Rack: bundle exec rackup config.ru
  4. Rakefile → bundle exec rake <task>

Framework Detection

SignalFramework
config/application.rbRails
config.ruRack
RakefileRake-based app

Rails-Specific

When config/application.rb is present:

  • Asset precompile: bundle exec rake assets:precompile (Sprockets or Propshaft)
  • API-only Rails (no asset pipeline gems) skip asset compilation
  • Bootsnap: bundle exec bootsnap precompile --gemfile during deps; bundle exec bootsnap precompile app/ lib/ during build

System Dependencies

Gem / useSystem dependency
pglibpq-dev
mysql2default-libmysqlclient-dev
rmagicklibmagickwand-dev
image_processing (vips)libvips-dev
charlock_holmeslibicu-dev, libxml2-dev, libxslt-dev

Asset Pipeline

GemBuild command
Sprocketsbundle exec rake assets:precompile
Propshaftbundle exec rake assets:precompile

Rails API-only (no sprockets-rails, propshaft) skip asset compilation.

Bootsnap

When bootsnap is in Gemfile:

  • During deps: bundle exec bootsnap precompile --gemfile
  • During build (Rails): bundle exec bootsnap precompile app/ lib/

Node.js Integration

If package.json detected, or execjs gem is used:

  • Install Node.js
  • Run npm install (or equivalent)
  • Execute build scripts
  • Prune dev dependencies

Common for Rails with Webpacker, Vite, or other frontend tooling.

Performance Optimizations

OptimizationWhen
jemallocInstall libjemalloc2 for improved memory allocation
YJITRuby 3.2+: may need rustc and cargo for compilation

Install Stage Optimization

Copy Gemfile + Gemfile.lock first for layer caching.

Caching

RUN --mount=type=cache,target=/usr/local/bundle \
    bundle config set --local path /usr/local/bundle \
    && bundle install --frozen

Base Images

StageImage
Buildruby:3.4-bookworm or ruby:3.4-alpine
Runtimeruby:3.4-slim or ruby:3.4-alpine

Dockerfile Patterns

Rails

FROM ruby:3.4-bookworm AS base

FROM base AS deps
WORKDIR /app
COPY Gemfile Gemfile.lock ./
RUN bundle config set --local path /usr/local/bundle \
    && bundle install --frozen

FROM base AS build
WORKDIR /app
COPY --from=deps /usr/local/bundle /usr/local/bundle
COPY . .
ENV RAILS_ENV=production
RUN bundle exec bootsnap precompile app/ lib/ \
    && bundle exec rake assets:precompile

FROM ruby:3.4-slim
WORKDIR /app
ENV RAILS_ENV=production
ENV BUNDLE_GEMFILE=/app/Gemfile
ENV GEM_HOME=/usr/local/bundle
ENV GEM_PATH=/usr/local/bundle
COPY --from=deps /usr/local/bundle /usr/local/bundle
COPY --from=build /app/public/assets /app/public/assets
COPY . .
EXPOSE 3000
CMD ["bundle", "exec", "puma", "-C", "config/puma.rb"]

Rack (config.ru)

FROM ruby:3.4-slim
WORKDIR /app
COPY Gemfile Gemfile.lock ./
RUN bundle config set --local path /usr/local/bundle \
    && bundle install --frozen
COPY . .
EXPOSE 9292
CMD ["bundle", "exec", "rackup", "config.ru", "-o", "0.0.0.0", "-p", "9292"]

Gotchas

  • Bundler version mismatch is a top build failure — always install the exact version from BUNDLED WITH in Gemfile.lock
  • Rails SECRET_KEY_BASE must be set even for asset precompilation — use a dummy value at build time: SECRET_KEY_BASE=dummy bundle exec rake assets:precompile
  • bundle exec is required in Docker CMD — running puma directly may use a system gem instead of the bundled one
  • jemalloc can reduce Rails memory usage 30-40% — LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.2 or install libjemalloc2
  • Bootsnap precompilation caches must happen AFTER gems are installed — running bootsnap precompile --gemfile before bundle install will fail silently