The configuration for the StorageClass looks like this:

```yaml
kind: StorageClass
apiVersion: storage.k8s.io/v1beta1
metadata:
 name: fast
provisioner: kubernetes.io/gce-pd
parameters:
 type: pd-ssd
 ```

This configuration creates a new StorageClass called “fast” that is backed by SSD volumes. The StatefulSet can now request a volume, and the StorageClass will automatically create it!

Deploy this StorageClass:

```
kubectl apply -f googlecloud\_ssd.yaml
 ```

**Headless Service**

Now you have created the Storage Class, you need to make a Headless Service. These are just like normal Kubernetes Services, except they don’t do any load balancing for you. When combined with StatefulSets, they can give you unique DNS addresses that let you directly access the pods! This is perfect for creating MongoDB replica sets, because our app needs to connect to all of the MongoDB nodes individually.

The configuration for the Headless Service looks like this:

```yaml
apiVersion: v1
kind: Service
metadata:
  name: mongo
  labels:
    name: mongo
spec:
  ports:
    - port: 27017
      targetPort: 27017
  clusterIP: None
  selector:
    role: mongo
 ```

You can tell this is a Headless Service because the clusterIP is set to “None.” Other than that, it looks exactly the same as any normal Kubernetes Service.

**StatefulSet**

The pièce de résistance. The StatefulSet actually runs MongoDB and orchestrates everything together. StatefulSets differ from Kubernetes [ReplicaSets](/docs/user-guide/replicasets/) (not to be confused with MongoDB replica sets!) in certain ways that makes them more suited for stateful applications. Unlike Kubernetes ReplicaSets, pods created under a StatefulSet have a few unique attributes. The name of the pod is not random, instead each pod gets an ordinal name. Combined with the Headless Service, this allows pods to have stable identification. In addition, pods are created one at a time instead of all at once, which can help when bootstrapping a stateful system. You can read more about StatefulSets in the [documentation](/docs/concepts/abstractions/controllers/statefulsets/).

Just like before, [this “sidecar” container](https://github.com/cvallance/mongo-k8s-sidecar) will configure the MongoDB replica set automatically. A “sidecar” is a helper container which helps the main container do its work.

The configuration for the StatefulSet looks like this:

```yaml
apiVersion: apps/v1beta1
kind: StatefulSet
metadata:
  name: mongo
spec:
  selector:
    matchLabels:
      role: mongo
      environment: test
  serviceName: "mongo"
  replicas: 3
  template:
    metadata:
      labels:
        role: mongo
        environment: test
    spec:
      terminationGracePeriodSeconds: 10
      containers:
      - name: mongo
        image: mongo
        command:
          - mongod
          - "--replSet"
          - rs0
          - "--smallfiles"
          - "--noprealloc"
        ports:
          - containerPort: 27017
        volumeMounts:
          - name: mongo-persistent-storage
            mountPath: /data/db
      - name: mongo-sidecar
        image: cvallance/mongo-k8s-sidecar
        env: