pulkitsinghal/sample-notifier-service

Demonstrate how a Notifier Service can allow browsers to maintain active websocket connections with it, so that later on it may let background workers notify those browser clients about the status of jobs/tasks

Run it

1. Bring up the development env for demo:
2. To tear down any previous runs: docker-compose -f docker-compose.local.yml down
3. To run: docker-compose -f docker-compose.local.yml up --build

Current Architecture

Pros

• No need for authentication in the notifier service as the socketId assigned to each webapp is just as random as any password and short lived (user may close the browser/tab when finished).

Cons

• The current notifier service does not scale well.
  • If we scaled up as-is then each instance will manage its own websocket connections
  • For example, docker-compose scale notifier=2:
    • notifier_1 will manage socketIds=[x,y,z]
    • notifier_2 will manage socketIds=[a,b,c]
    • a worker request to notify socketId=a might get routed to notifier_1 and that wouldn't be very helpful
      • if the notifier service was updated to be backed by a pub/sub queue so that workers could publish notifications to the queue directly and all the notifier instances could subscribe to the queue then notifier service would scale better.
• If socketId changes because the webapp is refreshed or the user restarts browser/tab:
  • Any background tasks that were kicked off before such an action will not be able to send notification. Because the previous websocket connection (referenced by the outdated socketId) will no longer be active.
  • To workaround this, we would need to ask notifier to work with username instead of socketId for notifications. Here's a diagram that zooms in on proposed changes. It does not show that the payload traveling between webapp > webserver > queue > worker > notifier will now contain username instead of socketId ... but hopefully that is obvious.

Alternatives

• socket-redis may be a great out-of-the-box scalable alternative to run as the notifier service