docs/deployment - provide example for solving PVC attach issue (#572)

- closes #499
- just convert the solution provided as recommendation to
  other users, tested on EKS running K8s version 1.23

docs/deployment.md

@@ -0,0 +1,19 @@
+# Deployment
+
+## Kubernetes
+
+Due to a limitation in how persistent volumes are handled in EKS, we have to ensure that both components sharing DB and CFG volumes are deployed to the same physical K8s node. This can be achieved by setting a `podAffinity` in the `values.yaml` file.
+
+```yaml
+# BUG: postee-0 und posteeui both need access to the same PVC (database) so we need to ensure both run on the same node
+affinity:
+  podAffinity:
+    requiredDuringSchedulingIgnoredDuringExecution:
+    - labelSelector:
+        matchExpressions:
+        - key: app.kubernetes.io/instance
+          operator: In
+          values:
+          - postee
+      topologyKey: kubernetes.io/hostname
+```