Kubernetes is a powerful tool. It can help you manage complex applications and provide you with the ability to easily automate tasks involved in managing them. In this course, we will start exploring Kubernetes from a beginner's standpoint. We will discuss what Kubernetes is and what it does, and we will work with some of the basic functionality of Kubernetes hands-on. We will build a simple Kubernetes cluster. We will also deploy a sample microservice application to the cluster in order to explore how Kubernetes can help easily manage such applications.

A Practical Guide to Kubernetes

## Updating the db Image

Let's see what happens when we `set` a new image to the `db` Pod.

kubectl set image \
    -f deploy/go-demo-2-db.yml \
    db=mongo:3.4 \
    --record

It'll take a while until the new image is pulled. 

## Describing the Deployment
Once it's done, we can `describe` the Deployment by checking the events it created.

kubectl describe \
    -f deploy/go-demo-2-db.yml

The last few lines of the **output** are as follows.

...
Events:
  Type    Reason             Age   From                   Message
  ----    ------             ----  ----                   -------
  Normal  ScalingReplicaSet  19m   deployment-controller  Scaled up replica set go-demo-2-db-75fbcbb5cd to 1
  Normal  ScalingReplicaSet  5m    deployment-controller  Scaled up replica set go-demo-2-db-f8d4b86ff to 1
  Normal  ScalingReplicaSet  0s    deployment-controller  Scaled down replica set go-demo-2-db-75fbcbb5cd to 0

We can see that it created a new ReplicaSet and that it scaled the old ReplicaSet to `0`. If, in your case, the last line did not appear, you'll need to wait until the new version of the `mongo` image is pulled.

Instead of operating directly on the level of Pods, the Deployment created a new ReplicaSet which, in turn, produced Pods based on the new image. Once they became fully operational, it scaled the old ReplicaSet to `0`. 

Since we are running a ReplicaSet with only one replica, it might not be clear why it used that strategy. When we create a Deployment for the API, things will become more evident.

## Looking into the Cluster

To be on the safe side, we might want to retrieve all the objects from the cluster.



# Updating the db Image

Let's see what happens when we `set` a new image to the `db` Pod.

It'll take a while until the new image is pulled. 

# Describing the Deployment
Once it's done, we can `describe` the Deployment by checking the events it created.

We can see that it created a new ReplicaSet and that it scaled the old ReplicaSet to `0`. If, in your case, the last line did not appear, you'll need to wait until the new version of the `mongo` image is pulled.

Instead of operating directly on the level of Pods, the Deployment created a new ReplicaSet which, in turn, produced Pods based on the new image. Once they became fully operational, it scaled the old ReplicaSet to `0`. 

Since we are running a ReplicaSet with only one replica, it might not be clear why it used that strategy. When we create a Deployment for the API, things will become more evident.

# Looking into the Cluster

To be on the safe side, we might want to retrieve all the objects from the cluster.



In this lesson, we will learn to update the Kubernetes Deployments.

Updating Deployments

Updating the db Image

Describing the Deployment