How to merge two Discourse sites

If you have two Discourse sites that you wish were one, this guide is for you.

There’s a tool called discourse_merger that can take one Discourse site and merge it into another.

Prereqs

This is not an easy task, and should be treated like any other migration to Discourse. You will not be running discourse_merger on a live production site. You will perform the merge in another environment where you can review the output before moving the result to production.

Copy vs Merge

Almost everything will be copied from one site to the other, but Categories and Users can be merged, which will avoid duplication.

  • Users will be merged if a user on both sites has the same email address.
  • Categories will be merged if they have the same name.

If you want to do any reorganization of your data, do it before merging.

Choose the destination site

Choose which site will be the destination for the data. This is the one that will retain all its styling and settings. The other site will have its users, categories, topics, posts, uploads, etc. copied/merged into the destination site.

How to do it

Take backups of both sites including files and copy them to the environment where you’ll perform the merge. It’s possible that they’re from different versions of Discourse, so we need them to be at the same version. I would choose to use the most recent version of Discourse while performing the merge.

Restore the destination site.

bundle exec ruby script/discourse restore destination-2018-08-02-134227-v2018xxx.tar.gz

Next we’ll extract the other site.

cd /path/to/data
tar xvzf other-2018-08-02-134227-v2018xxx.tar.gz

The output will include the database dump and the upload files.

Create a database with the data:

psql
CREATE DATABASE "copyme" ENCODING = 'utf8';
\q
gunzip < /path/to/data/other-2018-08-02-134227-v2018xxx.tar.gz | psql -d copyme

If you’re running the import in an official Docker container (recommended), you will need to reset the postgres password to provide it to the script, otherwise you may encounter an error that the postgres user cannot access the database.

To change the password:

sudo -u postgres psql
\password postgres
(enter the new password)
\q

Now it’s time to run the script. Some env variables you’ll set:

DB_NAME: name of database being merged into the destination site.
DB_HOST: (optional) hostname of database being merged. leave blank if it’s local.
DB_PASS: password for the postgres user to access the database
UPLOADS_PATH: absolute path of the directory containing “original” and “optimized” dirs. e.g. /path/to/data/uploads/default
SOURCE_BASE_URL: base url of the site being merged. e.g. https://meta.discourse.org
SOURCE_CDN: (optional) base url of the CDN of the site being merged.

You may need to run a bundle install prior to running the import script to avoid errors. To do so:

IMPORT=1 bundle install

On the first run, you might need to install some extra dependencies for the gems required in import.

Once the bundle is complete, run the import.

IMPORT=1 DB_NAME=copyme DB_PASS=password SOURCE_BASE_URL=http://copy.othersite.com UPLOADS_PATH=/shared/import/data/uploads/default bundle exec ruby script/bulk_import/discourse_merger.rb

When it’s done, review the output in a web browser.

You can use the remap tool to update links from the old forum.

bundle exec ruby script/discourse remap 'copy.othersite.com' 'hot.newsite.com'

Also rebake all posts with uploads:

rake posts:rebake_match["upload:"]

If everything looks good, take a backup of the result and restore it to your production server.

bundle exec ruby script/discourse backup
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