Updating the post in case someone stumbles across this post in the future.
I pulled the trigger on this today. In the end I decided I didn’t need to preserve the old db from Compose and my app has a feature that by default populates the tables with some core data anyway.
I first edited the mup.json, set the “setupMongo” to true and got rid of the MONGO_URL and MONGO_OPLOG_URL from the env config. I then tried to redeploy the app (via mup deploy) but the processed failed due to not being able to start mongod.
I re-executed mup setup and then redeployed without problems.
The only other thing of interest was that my little $5 droplet wasn’t able to handle the app now that it had to deal with the DB and would run out of memory and fail. I added a swap file and this took care of that.
$18/mo saved. I’ll come back to Compose in the future if I ever build an app that actually does get some users…