Let’s have a look to one of the typical micro-services deployment architecture in Kubernetes, that is deployed in Azure using Azure Kubernetes Service (AKS) and several other Azure Services like Storage, Key Vault, etc.
As a standard practice each deploy able change will go through several automated tests (sanity/regression/performance/etc.) in completely isolated environments. For every types of tests there are respective CI/CD pipelines.
Also sometime to re-produce customer Bugs, we might need to create an isolated environment manually from certain release (this we don’t foresee at the beginning of the project, however as project progresses we do see the need of it).