You can add and modify most elements of the original cluster specification provided that they translate to valid transformations of the underlying Kubernetes resources (e.g., existing volume claims cannot be downsized). The operator will attempt to apply your changes with minimal disruption to the existing cluster. You should ensure that the Kubernetes cluster has sufficient resources to accommodate the changes (extra storage space, sufficient memory and CPU resources to temporarily spin up new pods etc.).
For example, you can grow the cluster to three Elasticsearch nodes:
cat <<EOF | kubectl apply -f - apiVersion: elasticsearch.k8s.elastic.co/v1 kind: Elasticsearch metadata: name: quickstart spec: version: 7.15.1 nodeSets: - name: default count: 3 config: node.store.allow_mmap: false EOF