The plan to move to Google Cloud was in motion for many months, way before talks about a potential GitHub acquisition started.
They adopted Kubernetes relatively early, and as they progressed their reliance on Azure-specific services went down. At that point move to another cloud was a purely financial decision.
The move to k8s was not strictly a means to allow cloud migration. GitLab sells their Enteprise product, and the Kubernetes-based deployment helps customers with product trial and adoption. Cloud migration is a welcomed side-effect of that initiative.
I'd wager they got some kind of discount or exclusive pricing as well? Big ticket companies (which Gitlab could arguably be called in the tech world) moving to a cloud platform could generate a fair bit of buzz and free marketing?
They have a goals a section:
Goals of the GCP Migration Project
> In order of descending priority. Most important goals at the top.
1) Use the opportunity of an inter-cloud migration to make GitLab.com suitable for mission critical client workloads
Migrate GitLab.com from the Microsoft Azure Cloud platform to the Google Cloud while keeping downtime to a minimum
2) Use the same helm charts for GitLab.com as our EEP customers use
3) The goal here is for customers to be able to spin up a 10 person GitLab EEP instance in Kubernetes and scale it up to 100k users (or more) with little effort.
4) Use the migration as a marketing opportunity for GitLab Inc through creation of technical content
I'd be curious to hear if Microsoft buying GitHub had anything to do with it as well.