Allow specifying init_containers in Postgres CRD (zalando#445)

* Add support for init_containers

Author: redbaron

docs/user.md

@@ -273,6 +273,32 @@ are always passed to sidecars:
 
 The PostgreSQL volume is shared with sidecars and is mounted at `/home/postgres/pgdata`.
 
+
+## InitContainers Support
+
+Each cluster can specify arbitrary init containers to run. These containers can be
+used to run custom actions before any normal and sidecar containers start.
+An init container can be specified like this:
+
+```yaml
+apiVersion: "acid.zalan.do/v1"
+kind: postgresql
+
+metadata:
+  name: acid-minimal-cluster
+spec:
+  ...
+  init_containers:
+    - name: "container-name"
+      image: "company/image:tag"
+      env:
+        - name: "ENV_VAR_NAME"
+          value: "any-k8s-env-things"
+```
+
+`init_containers` accepts full `v1.Container` definition.
+
+
 ## Increase volume size
 
 PostgreSQL operator supports statefulset volume resize if you're using the

manifests/complete-postgres-manifest.yaml

@@ -4,6 +4,10 @@ kind: postgresql
 metadata:
   name: acid-test-cluster
 spec:
+  init_containers:
+  - name: date
+    image: busybox
+    command: [ "/bin/date" ]
   teamId: "ACID"
   volume:
     size: 1Gi

pkg/apis/acid.zalan.do/v1/postgresql_type.go

@@ -51,6 +51,7 @@ type PostgresSpec struct {
 	Databases            map[string]string    `json:"databases,omitempty"`
 	Tolerations          []v1.Toleration      `json:"tolerations,omitempty"`
 	Sidecars             []Sidecar            `json:"sidecars,omitempty"`
+	InitContainers       []v1.Container       `json:"init_containers,omitempty"`
 	PodPriorityClassName string               `json:"pod_priority_class_name,omitempty"`
 	ShmVolume            *bool                `json:"enableShmVolume,omitempty"`
 }

pkg/apis/acid.zalan.do/v1/zz_generated.deepcopy.go

@@ -410,6 +410,7 @@ func generatePodTemplate(
 	namespace string,
 	labels labels.Set,
 	spiloContainer *v1.Container,
+	initContainers []v1.Container,
 	sidecarContainers []v1.Container,
 	tolerationsSpec *[]v1.Toleration,
 	nodeAffinity *v1.Affinity,
@@ -428,6 +429,7 @@ func generatePodTemplate(
 		ServiceAccountName:            podServiceAccountName,
 		TerminationGracePeriodSeconds: &terminateGracePeriodSeconds,
 		Containers:                    containers,
+		InitContainers:                initContainers,
 		Tolerations:                   *tolerationsSpec,
 	}
 
@@ -803,6 +805,7 @@ func (c *Cluster) generateStatefulSet(spec *acidv1.PostgresSpec) (*v1beta1.State
 		c.Namespace,
 		c.labelsSet(true),
 		spiloContainer,
+		spec.InitContainers,
 		sidecarContainers,
 		&tolerationSpec,
 		nodeAffinity(c.OpConfig.NodeReadinessLabel),