Chapter 13

1. Assuming we have a Docker image in a registry for the two application services, the web API and Mongo DB, we then need to do the following:
   • Define a deployment for Mongo DB using a  StatefulSet; let's call this deployment db-deployment. The StatefulSet should have one replica (replicating Mongo DB is a bit more involved and is outside of the scope of this book).
   • Define a Kubernetes service called db of type ClusterIP for the db-deployment.
   • Define a deployment for the web API; let's call it web-deployment. Let's scale this service to three instances.
   • Define a Kubernetes service called api of type NodePort for web-deployment.
   • If we use secrets, then define those secrets directly in the cluster using kubectl.
   • Deploy the application using kubectl.

2. To implement layer 7 routing for an application, we ideally use an IngressController. The IngressController is a reverse proxy such as Nginx that has a sidecar listening on the Kubernetes Server API for relevant changes and updating the reverse proxy's configuration and restarting it, if such a change has been detected. We then need to define Ingress resources in the cluster which define the routing, for example from a context-based route such as  https://example.com/pets  to <a service name>/<port> pair such as  api/32001. The moment Kubernetes creates or changes this Ingress object, the IngressController's sidecar picks it up and updates the proxy's routing configuration.
3. Assuming this is a cluster internal inventory service:
   • When deploying version 1.0 we define a deployment called inventory-deployment-blue and label the pods with a label color: blue.
   • We deploy the Kubernetes service of type ClusterIP called inventory for the preceding deployment with the selector containing color: blue.
   • When ready to deploy the new version of the payments service, we first define a deployment for version 2.0 of the service and call it inventory-deployment-green. We add a label color: green to the pods. 
   • We can now smoke test the "green" service and when everything is OK, we can update the inventory service such as the selector contains color: green.
4. Some type of information that is confidential and thus should be provided to services through Kubernetes secrets include: passwords, certificates, API key IDs, API key secrets or tokens.
5. Sources for secret values can be files or base64 encoded values.