Adding the support for standby cluster

This will set up a continuous wal streaming cluster, by adding the corresponding section in postgres manifest. Instead of having a full-fledged standby cluster as in Patroni, here we use only the wal path of the source cluster and stream from there.

Since, standby cluster is streaming from the master and does not require to create or use databases of it's own. Hence, it bypasses the creation of users or databases.

There is a separate sample manifest added to set up a standby-cluster.

manifests/complete-postgres-manifest.yaml

@@ -66,7 +66,7 @@ spec:
   #  cluster: "acid-batman"
   #  timestamp: "2017-12-19T12:40:33+01:00" # timezone required (offset relative to UTC, see RFC 3339 section 5.6)
   #  s3_wal_path: "s3://custom/path/to/bucket"
-  
+
   # run periodic backups with k8s cron jobs
   # enableLogicalBackup: true
   # logicalBackupSchedule: "30 00 * * *"
@@ -86,4 +86,3 @@ spec:
   #    env:
   #      - name: "USEFUL_VAR"
   #        value: "perhaps-true"
-

manifests/standby-manifest.yaml

@@ -0,0 +1,20 @@
+
+apiVersion: "acid.zalan.do/v1"
+kind: postgresql
+metadata:
+  name: acid-standby-cluster
+  namespace: default 
+spec:
+  teamId: "ACID"
+  volume:
+    size: 1Gi
+  numberOfInstances: 1
+  postgresql:
+    version: "10"
+  # Make this a standby cluster and provide the s3 bucket path of source cluster for continuous streaming.
+  standby:
+    s3_wal_path: "s3://path/to/bucket/containing/wal/of/source/cluster/"
+
+  maintenanceWindows:
+  - 01:00-06:00 #UTC
+  - Sat:00:00-04:00