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Comment by TylerE | Hacker News Reader

Because most sites don’t want to spin up 100000 instances in 40 seperate data centers.

Why would you need 100K instances

If you run at web scale and serve ~10 million customers, you'll need a lot of servers to keep running. Most sites aren't anywhere near that.

Ya but say I'm a small business and only have 6 servers for my website

Why do I need to take all 6 offline to do maintenance?

Because you (accidentally or otherwise) built your infrastructure to need to. It's possible to build it so you don't have to, but most don't.

Because likely there is one master, authoritative data source and that has to go down at some point.

If you need to change something in your DB wouldn't you just have a job running in the background doing the migration and have your application code handle both cases when reading the DB (migrated/unmigrated)?

You say "just" like you think that sort of thing is easy. Nothing could be farther from the truth.

For one thing in many DBs certain (often nessesary) schema changes require a global write lock.

It's much much easier to just show down for 15 minutes or less than spend hundreds of hours of engineering effort.

10 million isn’t web scale though. Quite a few cities, many states and a bunch of smaller EU countries would have most of their b2c businesses, local government services and heck, even local newspapers serve 10 million people. That’s not web scale, that could be SQLite on one machine.

Tyler's point is that most companies don't have anywhere near the computing scale and workforce size which Amazon and Google have. Most companies don't have any option other than to take services offline during certain types of maintenance.

And why _exactly_ is that?

Why does the service need to be taken offline?

Because more instances costs more money and are more complex to orchestrate, costing even more money.

Most sites don't have the SLA or other reliability requirements that dictate crazy uptime. If they have no need, they won't structure their infrastructure for it because doing so is expensive. Big cloud companies have that figured out because their customers want it. Other, smaller sites feel that their money is better spent elsewhere.

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