How big is the vendor-lockin though? Let's say I want to use both Hetzner Cloud and GCP instances - I am sure it's possible, but the question is how much of a hassle it is ...
That depends on your app portfolio (naturally), how impacted it is by k8s version changes, and how much cloud specialization it requires.
You're probably better off on k8s than just about anything you didn't write yourself wrt to vendor lock-in. The true lock-in, IME, are when you use cloud features that aren't portable. Humble apps are fine, but ambitious apps are bound to those ambitious capabilities.
Seen next to comparable parallel installations it's a pretty minimal of per-environment specialization, and you can generally tweak the environments to support transparent parallel deployments. It's the differences in how load balancers work and which resources are immediately available that create work since the abstraction layer may not fully abstract away the environments.
Most of the issues I've faced (Ingress cough) have been solved by reading through the relevant pages in the Kubernetes documentation. A lot of the docs/tutorials provided by GCP link back there.
You're probably better off on k8s than just about anything you didn't write yourself wrt to vendor lock-in. The true lock-in, IME, are when you use cloud features that aren't portable. Humble apps are fine, but ambitious apps are bound to those ambitious capabilities.
Seen next to comparable parallel installations it's a pretty minimal of per-environment specialization, and you can generally tweak the environments to support transparent parallel deployments. It's the differences in how load balancers work and which resources are immediately available that create work since the abstraction layer may not fully abstract away the environments.