cass-operator | The DataStax Kubernetes Operator for Apache Cassandra

Yes, it's possible to change machine configuration later without downtime when using GKE cluster.

Have a look at the documentation Migrating workloads to different machine types:

A node pool is a subset of machines that all have the same configuration, including machine type (CPU and memory) authorization scopes. Node pools represent a subset of nodes within a cluster; a container cluster can contain one or more node pools.

When you need to change the machine profile of your Compute Engine cluster, you can create a new node pool and then migrate your workloads over to the new node pool.

and

To migrate your workloads without incurring downtime, you need to:

• Mark the existing node pool as unschedulable.
• Drain the workloads running on the existing node pool.
• Delete the existing node pool.

Kubernetes, which is the cluster orchestration system of GKE clusters, automatically reschedules the evicted Pods to the new node pool as it drains the existing node pool.

Note: This tutorial is only applicable if your container does not have Cluster Autoscaling enabled. If the Autoscaler adds or removes nodes while you are attempting a migration, you might not be able to mark all the nodes in the pool as unschedulable and drain them properly.

Detailed step by step instruction with commands and examples available at the documentation. To disable Cluster Autoscaling you can follow the documentation Disabling autoscaling for an existing node pool:

To output the stable external IP address under loadBalancer:ingress use the following command:

When you are deploying some application, one pod can have more than 1 container inside. If you will check Kubernetes Pod docs you can find 2 typs:

Pods that run a single container.

The "one-container-per-Pod" model is the most common Kubernetes use case; in this case, you can think of a Pod as a wrapper around a single container, and Kubernetes manages the Pods rather than the containers directly.

Pods that run multiple containers that need to work together.

A Pod might encapsulate an application composed of multiple co-located containers that are tightly coupled and need to share resources. These co-located containers might form a single cohesive unit of service--one container serving files from a shared volume to the public, while a separate "sidecar" container refreshes or updates those files. The Pod wraps these containers and storage resources together as a single manageable entity.

More information you can find in this docs.

How Pod configuration YAML with 2 containers looks like can be found here. In .spec.containers you can specify 2 or more containers.

Ive deployed those YAMLs.

Use -n parameter to specify correct namespace where the statfulset is deployed. Without the namespace it's trying to delete from default namespace where the statfulset cluster1-dc1-default-sts does not exist.

You can get pods by querying with selector like following