Apart from adding nodes, everything else remains consistent with Section 3: Update.

kubectl patch --type='merge' pxc polardbx-test -p '{"spec": {"topology": {"nodes": {"dn": {"replicas": 3}}}}}'

Similarly, the PHASE transitions from Running to Upgrading and then back to Running.

kubectl get pxc polardbx-test
NAME            GMS   CN    DN    CDC   PHASE      DISK   AGE
polardbx-test   1/1   1/2   2/3   2/2   Upgrading  6.2Gi  93s

However, you'll notice that the expected number of DN has changed to 2/3 and 3/3. Additionally, the operator automatically balances data, which may involve data migration. You can check the progress of data migration as follows:

kubectl get pxc polardbx-test -o wide
NAME           PROTOCOL   GMS   CN    DN    CDC   PHASE     DISK       STAGE           REBALANCE   VERSION                            AGE
polardbx-test  8.0        1/1   2/2   3/3   2/2   Upgrading 22.6 GiB   RebalanceWatch  50%          8.0.3-PXC-5.4.13-20220418/8.0.18   35d