Docker deployment in Ruby on Rails - Performance & Optimization

Performance: Docker deployment

MEDIUM IMPACT

Docker deployment affects the initial page load speed and server response time by controlling how the Rails app and its dependencies are packaged and started.

Deploying a Rails app with Docker for fast startup and minimal resource use

Ruby on Rails

FROM ruby:3.1-slim
RUN apt-get update && apt-get install -y --no-install-recommends nodejs yarn
WORKDIR /app
COPY Gemfile Gemfile.lock ./
RUN bundle install --without development test
COPY . .
CMD ["rails", "server", "-b", "0.0.0.0"]

Uses slim base image, installs only needed packages, caches bundle install, excludes dev/test gems to reduce image size and speed startup.

📈 Performance GainReduces image size by 300MB, container starts 5 seconds faster

Deploying a Rails app with Docker for fast startup and minimal resource use

Ruby on Rails

FROM ruby:3.1
RUN apt-get update && apt-get install -y nodejs
COPY . /app
WORKDIR /app
RUN bundle install
CMD ["rails", "server", "-b", "0.0.0.0"]

Installs unnecessary packages at build time and copies entire source including development files, causing large image size and slow startup.

📉 Performance CostAdds 500MB+ to image size, blocks container start for 10+ seconds

Performance Comparison

Pattern	Image Size	Startup Time	Resource Usage	Verdict
Full Ruby image with all packages	Large (700MB+)	Slow (10+ sec)	High CPU & Memory	[X] Bad
Slim Ruby image with cached dependencies	Smaller (400MB)	Faster (5 sec)	Lower CPU & Memory	[OK] Good

Rendering Pipeline

Docker deployment impacts server startup and response time, which affects when the browser receives HTML to start rendering.

→Server Startup

→Network Response

→Browser Rendering

⚠️ BottleneckServer Startup time inside the container

Core Web Vital Affected

LCP

Docker deployment affects the initial page load speed and server response time by controlling how the Rails app and its dependencies are packaged and started.

Optimization Tips

1Use minimal base images to reduce Docker image size.

2Cache dependencies like gems to avoid reinstalling on every build.

3Exclude development and test dependencies from production images.

Performance Quiz - 3 Questions

What Docker deployment practice helps reduce Rails app startup time?

A Using a slim base image and caching bundle install

B Installing all development and test gems in the image

C Copying the entire source code before installing dependencies

D Running bundle install on every container start

DevTools: Network

How to check: Open DevTools Network tab, reload page, and observe Time to First Byte (TTFB) and content download times.

What to look for: Long TTFB indicates slow server response, which can be caused by slow Docker container startup.