From a purely abstract point of view it's probably avoidable, but I'd conjecture many teams don't have the collective knowledge to effectively pull it off. Even if you plan things out carefully, something usually goes wrong :(. It only takes a small oversight to have it come crashing down. I think it's better to let your customers know ahead of time that you'll be performing maintenance, assume that something will go down, but still try to avoid it anyway.
MySQL only added support for online schema migrations with 5.6, prior to that you had to use a tool like pt-online-schema-change. I've heard claims (which I haven't verified, so it's entirely possible they are incorrect) of performance issues when performing migrations, which effectively bring the database down. Doesn't RDS sometimes require downtime for maintenance and upgrades? Is there any safe way around that?
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From a purely abstract point of view it's probably avoidable, but I'd conjecture many teams don't have the collective knowledge to effectively pull it off. Even if you plan things out carefully, something usually goes wrong :(. It only takes a small oversight to have it come crashing down. I think it's better to let your customers know ahead of time that you'll be performing maintenance, assume that something will go down, but still try to avoid it anyway.
MySQL only added support for online schema migrations with 5.6, prior to that you had to use a tool like pt-online-schema-change. I've heard claims (which I haven't verified, so it's entirely possible they are incorrect) of performance issues when performing migrations, which effectively bring the database down. Doesn't RDS sometimes require downtime for maintenance and upgrades? Is there any safe way around that?