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Port Forward Postgres Docker Container to Localhost

February 5, 2021

Tools - Install the following

Docker - A platform to run isolated software packages called containers.
Docker Postgres Image - The instructions for building a postgres container. A container is an instance of a docker image.

Intro

I recently pruned my docker containers and images to free up some space on my local drive. In doing so, I was required to spin up some of the containers that I rely on for local development.

One of these containers is a instance of postgres docker image. I prefer using a docker container of this image in replace of local postgres installations, as it is much less of a headache.

I also like to treat the postgres database in the container as if it were installed locally by forwarding the container port to localhost.

I find this helps limit configuration issues when working on new projects. Now all I will have worry about is my database username and password.

Command

terminal

docker run --name localhost-postgres -p 5432:5432 -e POSTGRES_USER=some_user -e POSTGRES_PASSWORD=some_password -d postgres

This entire command is not specific to postgres. You run commands like this using most one off docker images. Lets break this command down.

docker run Run a command in a new container
--name the custom name of the container ( I prefer to prefix it with localhost in case I have other postgres docker containers, NOT binded to localhost)
-d Run container in background and print container ID
-e Set environment variables
POSTGRES_USER= fill this value with username for your projects database configuration/secret files. (do not include the ENV variable in the command if you prefer to use default postgres as your username)
POSTGRES_PASSWORD= fill this value with the password for your projects database configuration/secret files. (this ENV variable is required for the container)
-p Publish a container’s port(s) to the host
5432:5432 The default container postgres port mapped (fowarded) to the default localhost postgres port 5432
postgres The installed postgres docker image you are using for the container

Using

Now all you have to do is is use the value for POSTGRES_USER= as your database username and POSTGRES_PASSWORD= as your database password.

rails_project/.env

DB_USER=some_user
DB_PASSWORD=some_password

And that is typically all I need to get up an running on a new project and run a command such as rake db:setup This is how a typical database configuration file looks in rails:

rails_project/config/database.yml

production:
  url:  <%= ENV["DATABASE_URL"] %>
  pool: <%= ENV["DB_POOL"] || ENV['RAILS_MAX_THREADS'] || 5 %>

development:
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  adapter: postgresql
  encoding: unicode
  database: rails_project
  host: localhost
  username: <%= ENV['DB_USER'] %>
  password: <%= ENV['DB_PASSWORD'] %>

test:
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  adapter: postgresql
  encoding: unicode
  database: rails_project_test
  host: localhost
  username: <%= ENV['DB_USER'] %>
  password: <%= ENV['DB_PASSWORD'] %>

Chris LaBarge