Automatically pick up the k8s pod namespace for DNS resolution.

The k8s DNS names contain the name of the namespace in which the pods
are deployed. The configs assumed that Dgraph is running in the
default namespace. This doesn't work when the config is deployed to
the non-default namespace.

By injecting the namespace name into the pod, we can automatically
use the correct namespace for DNS names in the command.

Author: danielmai

contrib/config/kubernetes/dgraph-ha.yaml

@@ -151,6 +151,11 @@ spec:
         volumeMounts:
         - name: datadir
           mountPath: /dgraph
+        env:
+          - name: POD_NAMESPACE
+            valueFrom:
+              fieldRef:
+                fieldPath: metadata.namespace
         command:
           - bash
           - "-c"
@@ -162,7 +167,7 @@ spec:
             if [[ $ordinal -eq 0 ]]; then
               dgraph zero --my=$(hostname -f):5080 --idx $idx --replicas 3
             else
-              dgraph zero --my=$(hostname -f):5080 --peer dgraph-zero-0.dgraph-zero.default.svc.cluster.local:5080 --idx $idx --replicas 3
+              dgraph zero --my=$(hostname -f):5080 --peer dgraph-zero-0.dgraph-zero.${POD_NAMESPACE}.svc.cluster.local:5080 --idx $idx --replicas 3
             fi
       terminationGracePeriodSeconds: 60
       volumes:
@@ -225,12 +230,20 @@ spec:
         volumeMounts:
         - name: datadir
           mountPath: /dgraph
+        env:
+          # This should be the same namespace as the dgraph-zero
+          # StatefulSet to resolve a Dgraph Zero's DNS name for
+          # Alpha's --zero flag.
+          - name: POD_NAMESPACE
+            valueFrom:
+              fieldRef:
+                fieldPath: metadata.namespace
         command:
           - bash
           - "-c"
           - |
             set -ex
-            dgraph alpha --my=$(hostname -f):7080 --lru_mb 2048 --zero dgraph-zero-0.dgraph-zero.default.svc.cluster.local:5080
+            dgraph alpha --my=$(hostname -f):7080 --lru_mb 2048 --zero dgraph-zero-0.dgraph-zero.${POD_NAMESPACE}.svc.cluster.local:5080
       terminationGracePeriodSeconds: 600
       volumes:
       - name: datadir

contrib/config/kubernetes/dgraph-single.yaml

@@ -79,12 +79,17 @@ spec:
         volumeMounts:
         - name: datadir
           mountPath: /dgraph
+        env:
+          - name: POD_NAMESPACE
+            valueFrom:
+              fieldRef:
+                fieldPath: metadata.namespace
         command:
           - bash
           - "-c"
           - |
             set -ex
-            dgraph alpha --my=$(hostname -f):7080 --lru_mb 2048 --zero dgraph-0.dgraph.default.svc.cluster.local:5080
+            dgraph alpha --my=$(hostname -f):7080 --lru_mb 2048 --zero dgraph-0.dgraph.${POD_NAMESPACE}.svc.cluster.local:5080
       terminationGracePeriodSeconds: 60
       volumes:
       - name: datadir