Fix nginx getting OOM killed

* Set requests.memory=256MiB  for the nginx-ingress-controller pod
We decided to leave limits open as this will allow to support most
of the generic use cases.
* QoS from Guaranteed to Burstable
This will make that application and ingress starve each other,
both fighting for node resources for an optimal usage of CPU
* Set priority class so that pods can take priority on a node that
might have No CPU taint.

task: 37625
story: 2006945

Change-Id: Ibc77ea64ad47f1a400d040f419f38bf52b9f0141
Signed-off-by: Diogo Guerra <diogo.filipe.tomas.guerra@cern.ch>

magnum/drivers/common/templates/kubernetes/helm/ingress-nginx.sh

@@ -104,12 +104,9 @@ data:
       replicaCount: 1
       minAvailable: 1
       resources:
-        limits:
-          cpu: 100m
-          memory: 64Mi
         requests:
-          cpu: 100m
-          memory: 64Mi
+          cpu: 200m
+          memory: 256Mi
       autoscaling:
         enabled: false
       customTemplate:
@@ -163,7 +160,7 @@ data:
             release: prometheus-operator
           namespace: kube-system
       lifecycle: {}
-      priorityClassName: ""
+      priorityClassName: "system-node-critical"
     revisionHistoryLimit: 10
     defaultBackend:
       enabled: true
@@ -182,9 +179,6 @@ data:
       replicaCount: 1
       minAvailable: 1
       resources:
-        limits:
-          cpu: 10m
-          memory: 20Mi
         requests:
           cpu: 10m
           memory: 20Mi
@@ -196,7 +190,7 @@ data:
         loadBalancerSourceRanges: []
         servicePort: 80
         type: ClusterIP
-      priorityClassName: ""
+      priorityClassName: "system-cluster-critical"
     rbac:
       create: true
     podSecurityPolicy:

releasenotes/notes/fix-nginx-getting-oom-killed-76139fd8b57e6c15.yaml

@@ -0,0 +1,11 @@
+---
+upgrade:
+  - |
+    nginx-ingress-controller QoS changed from Guaranteed to Burstable.
+    Priority class 'system-cluster-critical' or higher for
+    nginx-ingress-controller.
+fixes:
+  - |
+    nginx-ingress-controller requests.memory increased to 256MiB. This is a
+    result of tests that showed the pod getting oom killed by the node on
+    a relatively generic use case.