| We guess that such a client uses 1000 API calls per month (that's editing only), requires therefore 1GB of data in, and needs about 10 GB of traffic-related data out.
I agree with Sgoettschkes regarding Heroku, I've been using it in production for over a year without any issues at all and found it to be the lowest level of entry for scaling apps.
For example, I just spun up some new analytics software I wrote last week in golang and it peaks around 50k req/min, averages around 23k req/min, I'm using 4 nodes which realistically could probably handle 100k req/min without issue since in peak it's consuming about 50% of available resources to us as it is right now, but $100/mo is well worth it for the piece of mind, then combined with a $20/mo percona mysql server on digitalocean that averages around 4% cpu load, we're paying $120/mo to handle on the low end 927,360,000 http requests/month and all I have to do is a git push and the code automatically sets up the DB structure and DB indexes when booting the app up.
It's cool that they're using all these new technologies, but based on their numbers for me to have this software running on their setup it could realistically cost millions of dollars a month, and that's still removing the costs of cloudfront and s3 since it's not relevant in my case. Maybe on paper meshing a bunch of AWS technologies that big named companies use sounds great, but it seems like a high price to pay for the ability to say you're using these services.
I also think the costs are pretty high. Of course I have no idea how much traffic and requests where calculated, so I am just guessing. As cloudfront and S3 do the heavy lifting, a cheap server or two for actual editing of the content should be enough. And they don't need to scale on the same level as there won't be that much changing for customers, so paying more than 10,000$ for that with 100.000 customers seems pretty high.
But I get what the idea behind it was, and it seems to work pretty good. Also nice to have really low costs in the beginning :)