Yes. I once did zero downtime migration first from AWS to Google, then from Google to Hetzner for a client. Mostly for cost reasons: they had a lot of free credits, and moved to Hetzner when they ran out.
Their savings from using the credits were at least 20x what the migrations cost.
We did the migration by having reverse proxies in each environment that could proxy to backends each place, set up a VPN between them, and switched DNS. Trickiest part was the database failover and ensuring updates would be retried transparently after switching master.
Upside was that afterwards they had a setup that was provider agnostic and ready to do transparent failover of every part of the service, all effectively paid for through the free credits they got.
Their savings from using the credits were at least 20x what the migrations cost.
We did the migration by having reverse proxies in each environment that could proxy to backends each place, set up a VPN between them, and switched DNS. Trickiest part was the database failover and ensuring updates would be retried transparently after switching master.
Upside was that afterwards they had a setup that was provider agnostic and ready to do transparent failover of every part of the service, all effectively paid for through the free credits they got.