Here are my 2 cts.
I've used dokku for this, running Django, for years and recently I moved a customer over to use the digital ocean app platform.
There are a couple of things I find important when evaluating these platforms that I didn't see on the site: - is there database fail over with the multi server strong and powerful plans? - does appliku maintain the underlying servers and database? - is there monitoring?
At the moment databases in Appliku are best fit for non-production environments. So while you can enjoy easy and great deployments of your apps, I am not ready yet to compete on the production databases front. So no, we don't offer fail over or even backups at the moment. Backups are in plans, but more advanced features for databases is not even in backlog.
Rather than getting into all of that, your time here might be better spent here finding DBaaS services that host on the same clouds Appliku deploys to, and partnering Appliku with them to guarantee predictable network-transit peering to the clouds your users are launching on; probably by setting up the install-time UX flow so that that DBaaS choice is made early in the setup flow, and constrains further choices (i.e. user chooses DBaaS X; Appliku knows what AZs it exists in in each cloud, and restricts user to deploying the app to those same AZs in order to ensure free transit.)
In other words, do the backend work Heroku does to add a new DBaaS "add-on" partner, but without reselling/wrapping the resulting service, instead just giving a UX to bind to it.
But Appliku will keep being deployment solution for apps.
Admittedly, this works great for clusters of 1-10 machines. There's definitely some missing stuff that's hard to add for larger deployments.
But, I'd venture to say that most of Dokku's target audience doesn't need to worry about scaling past a couple of servers.