Multisite configuration with Docker

:warning: While multisite is supported in the Discourse application, this is an advanced sysadmin setup. If you don’t know what you’re doing, do not set up multisite. The Discourse team is unable to provide multisite configuration support.

If you wish to host multiple domains on a singled Docker setup, you’ll need a multisite configuration. Here are the basic building blocks for one.

Understand hooks

Multisite is a fairly advanced topic. Before attempting a multisite build, spend some time to learn about them.

Discourse templates use pups; its rules are simple and powerful.

Each rule you run may define a hook:

run:
  exec:
    cd: some/path
    hook: my_hook
    cmd:
      - echo 1

Later on in your container you can insert rules before or after a hook:

hooks:
  before_my_hook:
    - exec: echo "I ran before"
  after_my_hook:
     - exec: echo "I ran after"

So in the example above you will see output like the following:

I ran before
1
I ran after

You can read through the templates in /var/discourse/templates to see what hooks you have available.

Amend your standalone container to provision the second site tenant

Replace the entire hooks section with:

hooks:
  after_postgres:
     - exec: sudo -u postgres createdb b_discourse || exit 0
     - exec:
          stdin: |
            grant all privileges on database b_discourse to discourse;
          cmd: sudo -u postgres psql b_discourse
          raise_on_fail: false

     - exec: /bin/bash -c 'sudo -u postgres psql b_discourse <<< "alter schema public owner to discourse;"'
     - exec: /bin/bash -c 'sudo -u postgres psql b_discourse <<< "create extension if not exists hstore;"'
     - exec: /bin/bash -c 'sudo -u postgres psql b_discourse <<< "create extension if not exists pg_trgm;"'

  after_code:
    - exec:
        cd: $home/plugins
        cmd:
          - mkdir -p plugins
          - git clone https://github.com/discourse/docker_manager.git
  before_bundle_exec:
    - file:
        path: $home/config/multisite.yml
        contents: |
         secondsite:
           adapter: postgresql
           database: b_discourse
           pool: 25
           timeout: 5000
           db_id: 2
           host_names:
             - b.discourse.example.com

  after_bundle_exec:
    - exec: cd /var/www/discourse && sudo -E -u discourse bundle exec rake multisite:migrate

There are 3 hooks in play:

  1. after_postgres ensures that after postgres is installed an additional db called b_discourse is created with the appropriate permissions.

  2. before_bundle_exec, ensures docker_manager is in place and that the multisite.yml file is in place (which defines where to find the databases)

  3. after_bundle_exec, runs the custom db migration task rake multisite:migrate this ensures all the dbs are up to date.

Note on configuration

The above sample can be split into data container / app container if needed. Just run the after_postgres hook in the data container and the rest in web container.

The above sample can be extended to provision even more DBs. To do so, provision more DBs by duplicating the create db etc calls, and make sure you add additional sites in multisite.yml.

Make sure you amend the host_names node in multisite.yml to match the actual host name you wish to host.

Also, if you plan to run HTTPS, you will need a proxy in front of the site to handle it as the built in letsencrypt functionality will not work in a multisite scenario.

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