Creating a basic Rails app using PostgreSQL in a Docker container
I am working on several web apps using different technologies. One thing I really don't like to do is installing everything I need on my machine. I prefer to keep my machine as clean as possible. Therefore I was asking myself how to set up a Rails project using a different database than SQLite. So I decided to set up a Rails project following Daniela Baron's blog post "Setup a Rails Project with Postgres and Docker" which is pretty much the technology we are using in my current team as well.
As I was not able to set up a connection to the PostgreSQL inside the Docker container I thought I had to install the PostgreSQL client on my machine. As I am using homebrew setting this up was pretty straight forward:
brew install postgresqlThe next step would be creating the basic application structure of our Rails application. Please note that you have to specify which database you want to use. In our case it is PostgreSQL. You can set it up like this:
rails new rails_blog_pg --database=postgresqlBy executing the command
rails new rails_blog_pg --database=postgresqla new rails appliciation is creating using PostgreSQL as a database:
# config/database.yml
default: &default
adapter: postgresql
encoding: unicode
pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
development:
<<: *default
database: blogpg_development
test:
<<: *default
database: blogpg_test
production:
<<: *default
database: blogpg_production
username: blogpg
password: <%= ENV['BLOGPG_DATABASE_PASSWORD'] %>But there are some challenges we need to overcome. In order to be able to use our PostgreSQL database inside Docker we need to set up some additional data inside our database.yml configuration:
default: &default
adapter: postgresql
encoding: unicode
pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
database: <%= ENV['DATABASE_NAME'] || "blogpg" %>
username: <%= ENV['DATABASE_USER'] || "blogpg" %>
password: <%= ENV['DATABASE_PASSWORD'] || "blogpg" %>
port: <%= ENV['DATABASE_PORT'] || "5432" %>
host: <%= ENV['DATABASE_HOST'] || "127.0.0.1" %>
development:
<<: *default
port: 5434
test:
<<: *default
database: blogpg_test
port: 5434
production:
<<: *default
database: blogpg_production
username: blogpg
password: <%= ENV['BLOGPG_DATABASE_PASSWORD'] %>As we are using a docker compose file starting the container is pretty easy:
docker compose upYou should see something like this on your terminal:
WARN[0000] /Users/bjensen/Development/rails_blog_pg/docker-compose.yml: the attribute `version` is obsolete, it will be ignored, please remove it to avoid potential confusion
unable to get image 'postgres:14': Cannot connect to the Docker daemon at unix:///Users/bjensen/.docker/run/docker.sock. Is the docker daemon running?
bjensen@MMM2pro-Bjrn rails_blog_pg % docker compose up
[+] Running 15/15
✔ database Pulled 7.9s
✔ 7ce705000c39 Already exists 0.0s
✔ a17abc86e878 Already exists 0.0s
✔ 533f47cc37b3 Already exists 0.0s
✔ 2c171c713eb0 Already exists 0.0s
✔ ed0c27b12f94 Already exists 0.0s
✔ 6a797b38b71e Already exists 0.0s
✔ 04627f37bf24 Already exists 0.0s
✔ f51bf6ebfbc0 Already exists 0.0s
✔ 7a636815af7b Pull complete 5.9s
✔ 215c42f6b78a Pull complete 5.9s
✔ 267a3f8f7fab Pull complete 5.9s
✔ 90b4408a45e2 Pull complete 5.9s
✔ 7d7cee0a2c46 Pull complete 5.9s
✔ c207d0db79d4 Pull complete 5.9s
[+] Running 3/3
✔ Network rails_blog_pg_default Created 0.0s
✔ Volume "rails_blog_pg_db_pg_data" Created 0.0s
✔ Container rails_blog_pg-database-1 Created 0.2s
Attaching to database-1
database-1 | The files belonging to this database system will be owned by user "postgres".
database-1 | This user must also own the server process.
database-1 |
database-1 | The database cluster will be initialized with locale "en_US.utf8".
database-1 | The default database encoding has accordingly been set to "UTF8".
database-1 | The default text search configuration will be set to "english".
database-1 |
database-1 | Data page checksums are disabled.
database-1 |
database-1 | fixing permissions on existing directory /var/lib/postgresql/data ... ok
database-1 | creating subdirectories ... ok
database-1 | selecting dynamic shared memory implementation ... posix
database-1 | selecting default max_connections ... 100
database-1 | selecting default shared_buffers ... 128MB
database-1 | selecting default time zone ... Etc/UTC
database-1 | creating configuration files ... ok
database-1 | running bootstrap script ... ok
database-1 | performing post-bootstrap initialization ... ok
database-1 | syncing data to disk ... ok
database-1 |
database-1 |
database-1 | Success. You can now start the database server using:
database-1 |
database-1 | pg_ctl -D /var/lib/postgresql/data -l logfile start
database-1 |
database-1 | initdb: warning: enabling "trust" authentication for local connections
database-1 | You can change this by editing pg_hba.conf or using the option -A, or
database-1 | --auth-local and --auth-host, the next time you run initdb.
database-1 | waiting for server to start....2025-01-30 16:50:29.490 UTC [47] LOG: starting PostgreSQL 14.15 (Debian 14.15-1.pgdg120+1) on aarch64-unknown-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit
database-1 | 2025-01-30 16:50:29.490 UTC [47] LOG: listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
database-1 | 2025-01-30 16:50:29.492 UTC [48] LOG: database system was shut down at 2025-01-30 16:50:29 UTC
database-1 | 2025-01-30 16:50:29.494 UTC [47] LOG: database system is ready to accept connections
database-1 | done
database-1 | server started
database-1 |
database-1 | /usr/local/bin/docker-entrypoint.sh: running /docker-entrypoint-initdb.d/init.sql
database-1 | CREATE ROLE
database-1 |
database-1 |
database-1 | waiting for server to shut down....2025-01-30 16:50:29.634 UTC [47] LOG: received fast shutdown request
database-1 | 2025-01-30 16:50:29.635 UTC [47] LOG: aborting any active transactions
database-1 | 2025-01-30 16:50:29.636 UTC [47] LOG: background worker "logical replication launcher" (PID 54) exited with exit code 1
database-1 | 2025-01-30 16:50:29.636 UTC [49] LOG: shutting down
database-1 | 2025-01-30 16:50:29.645 UTC [47] LOG: database system is shut down
database-1 | done
database-1 | server stopped
database-1 |
database-1 | PostgreSQL init process complete; ready for start up.
database-1 |
database-1 | 2025-01-30 16:50:29.750 UTC [1] LOG: starting PostgreSQL 14.15 (Debian 14.15-1.pgdg120+1) on aarch64-unknown-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit
database-1 | 2025-01-30 16:50:29.750 UTC [1] LOG: listening on IPv4 address "0.0.0.0", port 5432
database-1 | 2025-01-30 16:50:29.750 UTC [1] LOG: listening on IPv6 address "::", port 5432
database-1 | 2025-01-30 16:50:29.751 UTC [1] LOG: listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
database-1 | 2025-01-30 16:50:29.752 UTC [62] LOG: database system was shut down at 2025-01-30 16:50:29 UTC
database-1 | 2025-01-30 16:50:29.756 UTC [1] LOG: database system is ready to accept connectionsCreating the initial database in Rails is easy. Just execute
rails db:createand you should have a working PostgreSQL database inside Docker. Let's check it. Just open a new terminal window and use the PostgreSQL we have installed using homebrew:
psql -h 127.0.0.1 -p 5434 -U blogpg
# enter password from init.sqlUse the \l command to list all databases and you should see the folling:
blogpg=> \l
List of databases
Name | Owner | Encoding | Locale Provider | Collate | Ctype | Locale | ICU Rules | Access privileges
-------------+----------+----------+-----------------+------------+------------+--------+-----------+-----------------------
blogpg | blogpg | UTF8 | libc | en_US.utf8 | en_US.utf8 | | |
blogpg_test | blogpg | UTF8 | libc | en_US.utf8 | en_US.utf8 | | |
postgres | postgres | UTF8 | libc | en_US.utf8 | en_US.utf8 | | |
template0 | postgres | UTF8 | libc | en_US.utf8 | en_US.utf8 | | | =c/postgres +
| | | | | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | libc | en_US.utf8 | en_US.utf8 | | | =c/postgres +
| | | | | | | | postgres=CTc/postgres
(5 rows)
blogpg and blogpg have been created using
rails db:createSo it seems that everything is working.
In order to connect our Rails application with the PostgreSQL inside Docker we need to set up different things.
As we are building a web application we need to set up what should happen when opening up the application:
Rails.application.routes.draw do
root "articles#index"
get "/articles", to: "articles#index"
endIn this case the articles index page will be the default (root) route to take.
Calling a route will lead to call a controller in rails that should invoke a model in order to display data. As we don't have it right now we need to create it. Luckily rails can use scaffolding to make this easy:
bin/rails generate controller Articles index --skip-routes
bin/rails generate model Article title:string body:textGenerating a model will lead to generate the related database migration files as well. And the database needs to be migrated in order to make everything work:
rails db:migrateIn order to verify that everything worked we can use the PostgreSQL as we did before. Now you should see something like this:
blogpg=> \dt
List of relations
Schema | Name | Type | Owner
--------+----------------------+-------+--------
public | ar_internal_metadata | table | blogpg
public | articles | table | blogpg
public | schema_migrations | table | blogpg
Till now our database is empty. Thanks to rails there is a nice way to add some data. Let's use
rails consoleNow we can add some data:
Article.create(
title: "Hello Postgres Docker",
body: "I'm being created in Postgres running in a Docker container"
)Let's validate that we have the data in our database:
blogpg=> select * from articles;
id | title | body | created_at | updated_at
----+-----------------------+-------------------------------------------------------------+----------------------------+----------------------------
1 | Hello Postgres Docker | I'm being created in Postgres running in a Docker container | 2025-01-30 16:59:09.497067 | 2025-01-30 16:59:09.497067
(1 row)
As you can see the data is there.
In order to be able to see our data in the web application we need to tell the rails application what to display. We do this in the related controller:
# app/controllers/articles_controller.rb
class ArticlesController < ApplicationController
def index
@articles = Article.all
end
endNow we need to tell rails how to display this data. Therefore we have to modify the related view file in a way we like:
<!-- app/views/articles/index.html.erb -->
<h1>Articles</h1>
<table>
<tr>
<th>Title</th>
<th>Body</th>
</tr>
<% @articles.each do |article| %>
<tr>
<td><%= article.title %></td>
<td><%= article.body %></td>
</tr>
<% end %>
</table>If you open the webbrower on 127.0.0.1:3000 you should see this:
Congratulations! You're done setting everything up using PostgreSQL inside a Docker container.
- "Setup a Rails Project with Postgres and Docker" - The blogpost that I worked through in order to understand how this works
- Rails - The framework used to create the blog
- PostgreSQL - The database used in this example
- Docker - The container technology used because I didn't want to install and run PostgreSQL locally on my computer