Helm chart improvements (#927)

* Added sample values in comments.

* Added affinity and improved tolerations.

charts/zalenium/templates/_pod-template.yaml

@@ -158,11 +158,12 @@ spec:
   nodeSelector:
     {{ .Values.nodeSelector.key }}: {{ .Values.nodeSelector.value | quote }}
   {{- end }}
-  {{- if .Values.tolerations.enabled }}
+  {{- if .Values.tolerations }}
   tolerations:
-    - key: {{ .Values.tolerations.key }}
-      operator: {{ .Values.tolerations.operator }}
-      value: {{ .Values.tolerations.value | quote }}
-      effect: {{ .Values.tolerations.effect }}
+{{ toYaml .Values.tolerations | indent 4 }}
   {{- end }}
+  {{- if .Values.affinity }}
+  affinity:
+{{ toYaml .Values.affinity | indent 4 }}
+  {{- end -}}
 {{- end }}

charts/zalenium/values.yaml

@@ -63,6 +63,7 @@ hub:
   desiredContainers: 2
   maxDockerSeleniumContainers: 10
   videoRecordingEnabled: true
+  # the limits/requests below are for Selenium pods (containers)
   cpuRequest: 250m
   cpuLimit: 1000m
   memRequest: 500Mi
@@ -176,10 +177,38 @@ nodeSelector:
   ## key: test
   ## value: test
 
-tolerations:
-  enabled: false
-  ## Set tolerations to run zalenium hub on nodes with taints
-  ## key: test
-  ## operator: Equal
-  ## value: test
-  ## effect: NoSchedule
+# Allow pods to run on nodes with taints
+# https://kubernetes.io/docs/concepts/configuration/taint-and-toleration/
+#
+# tolerations:
+# - key: "<key-name>"
+#   operator: "Equal"
+#   value: "<key-value>"
+#   effect: "NoSchedule"
+
+# More flexible way to manage pods' allocation
+# https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#affinity-and-anti-affinity
+#
+# affinity:
+#   # soft preference to go to dedicated nodes
+#   nodeAffinity:
+#     preferredDuringSchedulingIgnoredDuringExecution:
+#     - weight: 100
+#       preference:
+#         matchExpressions:
+#         - key: <key-name>
+#           operator: In
+#           values:
+#           - <key-value>
+#   # prefer not to start the pod on a node that's having another pod with specific labels
+#   podAntiAffinity:
+#     preferredDuringSchedulingIgnoredDuringExecution:
+#     - weight: 100
+#       podAffinityTerm:
+#         labelSelector:
+#           matchExpressions:
+#           - key: <key-name>
+#             operator: In
+#             values:
+#             - <key-value>
+#         topologyKey: "kubernetes.io/hostname"