* Flask + Flask-Login + Flask-SQLAlchemy [1]
* uWSGI app servers [2]
* Nginx web servers [3]
* Dramatiq/Celery with RabbitMQ for background tasks
* Combination of Postgres, S3, and DigitalOcean Spaces for storing customer data [4]
* SSDB (disk-based Redis) for caching, global locks, rate limiting, queues and counters used in application logic, etc [5]
I like how OP shows the service providers he uses, and why he decides not to self-host those parts of his infra. Also, there's a large up front cost involved for any stack (Rails, Django, k8s). I'd be interested in a more detailed writeup with configs, to try out OP's auto-scaling setup. My configs are linked in the gist below [2] for my non-auto-scaling Flask setup.
I spend about $4,000/mo on infra costs. S3 is $400/mo, Mailgun $600/mo, and DigitalOcean is $3,000/mo. Our scale/server load might be different, but I'm still interested in what the costs would be with your setup.
[1] https://wakatime.com/blog/33-flask-part-2-building-a-restful...
[2] https://gist.github.com/alanhamlett/ac34e683efec731990a75ab6...
[3] https://wakatime.com/blog/23-how-to-scale-ssl-with-haproxy-a...
[4] https://wakatime.com/blog/46-latency-of-digitalocean-spaces-...
[5] https://wakatime.com/blog/45-using-a-diskbased-redis-clone-t...