It’s been a few years since I used keepalived so my knowledge might be outdated.
You are correct that the VMs should be in different servers. To test around you can set up on the same, but this shouldn’t be done in production environments, if you lose the host, you lose the service.
Keepalived will make sure your service is available in an IP. To say, you have two (it can be configured for more than two) servers with (A) 192.168.0.2 and (B) 192.168.0.3 which provide the service you want to provide. With Keepalived you’ll configure a common IP for both of them, let’s say 192.168.0.4
While working, server A will be available at 192.168.0.2 and 192.168.0.4 while server B will be available at 192.168.0.3. If server A fails keepalived will “move” 192.168.0.4 to server B, so 192.168.0.2 will not be available and server B will be available at 192.168.0.3 and 192.168.0.4.
No matter which server is up / primary, your service will always be available at 192.168.0.4
For the mirroring part, you need to solve it in another step outside from keepalived. For example, MariaDB provides multimaster replication “out of the box” with galera (the recommendation is at least 3 nodes)
For files, depending on your filesystem you should have to rsync, use some shared units, distribute filesystem (Ceph), …
At least, I understood it in some other way.
With some “back of the envelope” calculations (using Reddit provided revenue and user number) Reddit’s revenue (not earnings) / user month is $0.12 , around $1.4 user/year
In the case of Apollo, the “intended” revenue per Apollo user would be $2.5 per user month, around $30 user /year
From the body of the post, search for the following header: Why do you say Reddit’s pricing is “too high”? By what metric?
The $20 Million is what would cost to continue using the API with the intended price point.
Also, $500.000 year would be revenue, not earnings. As I understood, he’s not a “solo” developer working in his basement. There’s people and infraestructure to pay from that number (I don’t know neither how many people nor how much costs “keeping the lights on”, but anyway, I don’t think those numbers are relevant)
My own opinion: Let’s say Reddit’s break even point is around the Apollo’s intended cost / user. That would mean that with a revenue of $0.12 per month * user, Reddit would be losing around $800 million / month. That’s close to $10.000 million / year. Even as a ballpark figure, I find it suspicious to say the least.
BTW: I’ve never used Apollo. RIF user from long long before they had to change the App name