This is a how-to guide that will walk you through the process of setting up environmental variables in a self-hosted Discourse Installation.
Environmental variables are a crucial part of configuring your Discourse instance, and they can be used to store sensitive information such as API keys and database passwords.
Adding environmental variables to a .yml (YAML) file is straightforward. Here’s a basic example:
# This is a YAML file with environmental variables
env:
VARIABLE_NAME: "Variable Value"
ANOTHER_VARIABLE: "Another Value"
In the context of a Discourse Docker container, environmental variables are stored in the env section of your app.yml file.
Here's an example of an app.yml file:
## this is the all-in-one, standalone Discourse Docker container template
##
## After making changes to this file, you must rebuild
## /var/discourse/launcher rebuild app
##
templates:
- "templates/postgres.template.yml"
- "templates/redis.template.yml"
- "templates/web.template.yml"
- "templates/web.ratelimited.template.yml"
## Uncomment these two lines if you wish to add Lets Encrypt (https)
#- "templates/web.ssl.template.yml"
#- "templates/web.letsencrypt.ssl.template.yml"
## which TCP/IP ports should this container expose?
## If you want Discourse to share a port with another webserver like Apache or nginx,
## see https://meta.discourse.org/t/17247 for details
expose:
- "80:80" # http
- "443:443" # https
params:
db_default_text_search_config: "pg_catalog.english"
## Set db_shared_buffers to a max of 25% of the total memory.
## will be set automatically by bootstrap based on detected RAM, or you can override
db_shared_buffers: "256MB"
env:
LANG: en_US.UTF-8
# DISCOURSE_DEFAULT_LOCALE: en
## How many concurrent web requests are supported? Depends on memory and CPU cores.
## will be set automatically by bootstrap based on detected CPUs, or you can override
UNICORN_WORKERS: 3
## TODO: The domain name this Discourse instance will respond to
DISCOURSE_HOSTNAME: 'discourse.example.com'
## Uncomment if you want the container to be started with the same
## hostname (-h option) as specified above (default "$hostname-$config")
#DOCKER_USE_HOSTNAME: true
## TODO: List of comma delimited emails that will be made admin and developer
## on initial signup example 'user1@example.com,user2@example.com'
DISCOURSE_DEVELOPER_EMAILS: 'user@example.com'
## TODO: The SMTP mail server used to validate new accounts and send notifications
DISCOURSE_SMTP_ADDRESS: smtp.example.com # (mandatory)
DISCOURSE_SMTP_PORT: 587 # (optional)
DISCOURSE_SMTP_USER_NAME: user@example.com # (optional)
DISCOURSE_SMTP_PASSWORD: a_s3cr3t_p@ssword # (optional)
#DISCOURSE_SMTP_ENABLE_START_TLS: true # (optional, default true)
## If you added the Lets Encrypt template, uncomment below to get a free SSL certificate
#LETSENCRYPT_ACCOUNT_EMAIL: me@example.com
## The CDN address for this Discourse instance (configured to pull)
#DISCOURSE_CDN_URL: //discourse-cdn.example.com
## The Docker container is stateless; all data is stored in /shared
volumes:
- volume:
host: /var/discourse/shared/standalone
guest: /shared
- volume:
host: /var/discourse/shared/standalone/log/var-log
guest: /var/log
## Plugins go here
## see https://meta.discourse.org/t/19157 for details
hooks:
after_code:
- exec:
cd: $home/plugins
cmd:
- git clone https://github.com/discourse/docker_manager.git
## Any custom commands to run after building
run:
- exec: echo "Beginning of custom commands"
## If you want to set the 'From' email address for your first registration, uncomment and change:
#- exec: rails r "SiteSetting.notification_email='info@unconfigured.discourse.org'"
## After getting the first signup email, re-comment the line. It only needs to run once.
- exec: echo "End of custom commands"
Let’s get started with adding environmental variables to your site! 
The following instructions are written for a Standard Discourse Installation
Login to Your Server
Use a tool like PuTTY or the terminal on Unix-based systems to SSH into your server.
ssh username@your-server-ip
Navigate to the Discourse Directory
Once you have access to your server, navigate to the directory containing your Discourse Docker setup, this is typically located at /var/discourse.
cd /var/discourse
Open the app.yml File
You’ll need to open the app.yml file in a text editor. For this example we’ll be using nano.
nano containers/app.yml
Add Your Environmental Variables
In the app.yml file, you’ll find an env section. This is where you can add your environmental variables.
env:
DISCOURSE_HOSTNAME: 'discourse.example.com'
DISCOURSE_SMTP_ADDRESS: smtp.example.com
DISCOURSE_SMTP_PORT: 587
DISCOURSE_SMTP_USER_NAME: user@example.com
DISCOURSE_SMTP_PASSWORD: a_s3cr3t_p@ssword
For example, if you wanted to set the DISCOURSE_ENABLE_CORS environmental variable to true to enable Cross-Origin Resource Sharing (CORS), you would add the following line to the env section:
env:
DISCOURSE_ENABLE_CORS: "true"
...
The whitespace and formatting is important here, so make sure to maintain the correct indentation (two spaces) for the new line
Once you’ve modified your variables, save and close the file.
Rebuild the Discourse Container
Finally, you’ll need to rebuild your Discourse Docker container for the changes to take effect. You can do this with the following command:
./launcher rebuild app
Alternatively, to update environmental variables for a running container without rebuilding, you can also use:
./launcher destroy app
./launcher start app
After the rebuild process completes, your updated environmental variables will be available to your Discourse application! 
