Something I've always wondered about<p>Big cloud platforms never take the service down for maintenance<p>They do any upgrades or maintenance live on the running service<p>If this is possible for them, why do so many websites have scheduled maintenance where they take the whole site down?<p>Are the engineers just not able to figure out how to do the maintenance without turning off the website?<p>What is the secret that these cloud platforms have discovered where they don't need scheduled maintenance like the rest of the web?
If the military has fighters that can refuel in the air, why does United refuel on the ground like chumps?<p>First of all, sometimes even AWS makes mistakes and has downtime. They have downtime (usually unplanned) fairly often. Companies like VISA, that do payment processing, where countless dollars could be lost in just a few minutes of downtime, almost never update their old systems. They still have programs running FORTRAN. When they do update, it's complicated.<p>You can try to get really good uptime by doing things like forking your database and replicating your commit log to the fork. You can do rolling updates, where different customers are served different versions of a system. You can do extremely thorough testing.<p>But are you? Can you afford to do that and do you even have the engineering talent to make it happen even if you want to? Are you going to pass on new business opportunities and new features just to avoid a 20 minute downtime for a database migration at 2am? I suspect you are not.
You can stretch availability to 99.9999999 if you have the money and the team to support it. However, each jump can incur up to a 100x cost increase per the Google SRE book. Availably is always a conversation about risk, innovation, cost, and what your customers will accept as an SLA.<p>Even Google doesn't go 99.999 on all services. Services that require rapid innovation are always lower because availability incurs an opportunity cost on innovation.
It generally takes more prep work to do maintenance without downtime (i.e. it’s more expensive), and if you’re not operating at their scale, it’s less likely to be worth it.