As we saw during the Google Cloud Compute outage on June 2nd, 2019, even seemingly-infallible titans like Google can be brought down.
Because Shopify is a Google Cloud customer, Shopify fell with Google.
This never happens.
— Shopify Support to my Shopify Plus customer during the outage
Well, that just happened.
Downtime due to one provider is to be expected, even if Google is the provider. And yet it's very avoidable: High Availability technologies have come a long way in recent years. With software like HAProxy & MySQL/MariaDB clustering it should be possible for Shopify to sustain outages.
Unfortunately, because Shopify is a software-as-a-service (SaaS) product hosted by Shopify on servers under Shopify's control, Shopify customers (even Shopify Plus customers) have no control over the server infrastructure used by Shopify to power online stores.
Short of migrating away from Shopify, there is absolutely nothing you can do to control when your Shopify store goes down.
Maybe it's not worth it for every business. I work with mid-sized e-commerce businesses who would lose thousands of dollars for every hour of downtime.
This is unacceptable to them. If this is unacceptable to you, too, please get in touch.
Alternative (Less-Insane, More-Reasonable) Step Two: Point the load balancer to a custom landing page explaining that your store is down for maintenance, but offering an extra-special coupon code to anyone that signs up for your mailing list.
Step Three: Sit back and relax while you laugh at the mere mortals on Shopify who didn't have a failover plan in place. If you need help with sitting back and relaxing, we recommend consulting a medical professional. Sorry, can't help you. But peace of mind we can give you, so there is that.