Problem Description
I was recently setting up a new CDN service and configuring DISCOURSE_LONG_POLLING_BASE_URL in app.yml, for separating the long polling service to the original server.
But the message bus continues to make requests to “/” instead of respecting the configured long polling base URL.
Steps to Reproduce
- Configure
DISCOURSE_LONG_POLLING_BASE_URLinapp.ymlwith a custom CDN URL - Rebuild and start Discourse
- Verify that the frontend correctly reads the environment variable value
- Observe message bus network requests in browser dev tools
Some screenshots
Frontend correctly reading the setting:
Expected Behavior
Message bus should use the configured long_polling_base_url setting for its requests when the setting is provided.
Actual Behavior
Message bus continues to make requests to “/” regardless of the DISCOURSE_LONG_POLLING_BASE_URL configuration.
Root Cause
The issue is in app/assets/javascripts/discourse/app/instance-initializers/message-bus.js.
The logic for setting messageBus.baseUrl was not properly handling the long_polling_base_url site setting, causing it to default to / even when a custom URL was configured.
Fix
I’ve identified and fixed the issue in the message bus instance initializer. The fix ensures that when siteSettings.long_polling_base_url is set and not equal to “/”, it properly configures the message bus base URL.
Verification
- Confirmed the frontend correctly reads the environment variable
- Fixed the message bus initialization logic to respect the setting
- All formatting checks pass
- Message bus now correctly uses the configured long polling base URL
This bug affects any Discourse installation using a custom CDN setup with long polling, preventing proper CDN utilization for message bus requests.
Thanks to @David_Ghost, please head over to our discussion here: