Synology on Rails Part I: Running

12 December 2023 about a 5 minute read

Following my last post, I was ready to deploy an early version of my Meal Planning/Recording Rails app. Given this is a small app, with really only two users, I didn’t feel it necessary to pay to deploy it to the cloud and to do the work needed to secure it for cloud hosting.

I knew that I could run containerized apps on my Synology NAS. So I just needed to figure out howto get Rails and my app containerized and deployed.

What I Wanted

  • Rails app running in a container on the NAS
  • The SQLite file not in the container
  • Access inside my home network
  • Automatable deployment

What I Had

  • A Rails app using a SQLite database
  • A Mac Mini M2 for development
  • A Synology NAS with an Intel processor running DSM 7.2
  • Me, who despite working at Pivotal on container-based technology, only had a conceptual understanding of all of these pieces working together.

What I Did

First, I needed an image.

1. Install Docker on MacOS

I installed the Homebrew Cask version of Docker

$ brew install --cask docker

I ran Docker, keeping the Docker daemon running in the background on MacOS.

2. Getting The Rails 7.1 Dockerfile

Rails 7.1 ships with a Dockerfile. I built the app with Rails 7.0, but have since upgraded to 7.1, so I generated a new app and copied these two key files:

  • ./Dockerfile
  • ./bin/docker-entrypoint

I’m using cssbuild to turn my SASS into CSS. I decided to keep Node and Yarn out of the container for size, which means I made this change to the Dockerfile to comment out the asset compilation:

# Precompiling assets for production without requiring secret RAILS_MASTER_KEY 
#RUN SECRET_KEY_BASE_DUMMY=1 ./bin/rails assets:precompile

I’ll deal with assets later.

3. Building the Image

It’s possible to build an Intel-targeted container on Apple silicon. Very simple:

$ docker buildx build --platform linux-amd64 -t <tag-name>

However, the when bundling, Bundler complained that the Gemfile needed to support Intel processors. This line adds this support:

$ bundle lock --add-platform x86_64-linux

Then the image build just worked and was in Docker locally. Then I was able to push the image to Docker Hub in the GUI.

4. Running the Image on Synology DSM

I followed this guide to better understand how containers, and the Container Manager, work on Synology. I applied this knowledge by:

  1. Updated Synology DSM to 7.2+
  2. Installed the Container Manager package
  3. Installed the Web Station package
  4. Imported my image from Docker Hub
  5. Ran that image to get a booted container

This almost worked. Everything was good until step 5. The Container Manager had all of the environment variables. Port 3000 was exposed.

I followed the prompts in the UI and made a named Web Station Web Portal - I called it meals.local that pointed to the Container. I also updated my local DNS - I use a Firewalla at home - so that meals.local pointed to my NAS’s IP address.


But Rails wouldn’t start because I didn’t have the master key. This was a simple setting in the Container Manager app, adding a RAILS_MASTER_KEY environment variable and manually copying the key over from config/master.key.

I saved and restarted the container.

6. Whoops - The Database

Now Rails wouldn’t start because there was no database. I did the following:

  1. Created and migrated the production database file in db/production/production.sqlite3 on my dev machine
  2. Updated config/database.yml:
  <<: *default  
  database: db/production/production.sqlite3
  1. Downloaded a Rails .dockerignore (thanks yizeng!) and added db/production to it
    • This keeps the production SQLite file out of the container
  2. Created a directory for my app on the NAS
    • Synology Container Manager makes a directory called /docker, so I made /docker/meals
  3. Shared /docker so I could see it on my network, thus able to copy files from my development machine
  4. Copied production.sqlite to /docker/meals/db/production.sqlite3
  5. Rebuilt the image and uploaded to Docker Hub

From there I was able to stop and delete the container, then update the image from Docker Hub. Before I started it I had to make a container Settings change in Container Manager:

  1. Map a mount point in Container Manager (Container - Settings - Volume Settings in the GUI) for the container so that /rails/db/production in the container pointed to /docker/meals/db on the NAS.

I rebuilt and restarted again.

7. Whoops - Users and File Permissions

Rails still wouldn’t start. This time it was because the rails user, which the Dockerfile creates, didn’t exist. Back to Synology DSM.

  1. Created a user named rails in the users group
  2. Fount the rails user id and group id - I had to sudo to the NAS for this
  3. Updated the Dockerfile’s “useradd” area like this:
# Run and own only the runtime files as a non-root user for security  
# Synology DSM - make a user called 'rails' and save its id (will need to ssh/terminal for this)  

ARG UID=132 # sudo and find this  
ARG GID=100 # likely this value, but sudo and set properly  

RUN useradd -m -u $UID -g $GID --create-home --shell /bin/bash rails && \  
    chown -R rails:users db log storage tmp public

# Switch to this user
USER rails:users

Then I had to do the manual cycle of build image, push image, stop container, delete container, update image, run image, change container settings.

But the app booted and worked! I could visit https://meals.local and see my app. Victory!

This was a lot of trial and error. And I was tired of all the manual building, copying, and GUI work.

Next post: automating the deploy.

This article is part of the series Synology on Rails and is tagged with web development, ruby, rails, software engineering, and deployment.