IMPORTANT:
Some of the content here is a personal summary/abbreviation of contents on the Official Kubernetes Guide. Feel free to refer to that site if you think some of the sections written here are not clear.
Note
- this content assumes some prior knowledge on Docker, including Docker Compose.
Installation
Please follow this link: https://kubernetes.io/docs/tasks/tools/
- it is recommended that you install kubectl, which allows you to run commands against Kubernetes clusters.
Kubernetes Basics
Kubernetes Clusters
- Kubernetes coordinates a highly available cluster of computers that are connected to work as a single unit.
A Kubernetes cluster consists of two types of resources:
- The Master coordinates the cluster
- Nodes are the workers that run applications
- A node is a VM or a physical computer that serves as a worker machine in a Kubernetes cluster
- Each node has a
Kubelet
, which is an agent for managing the node and communicating with the Kubernetes master.
Starting with Minikube
This tutorial shows you how to run a sample app on Kubernetes using minikube
and Katacod
.
Objectives
- Deploy a sample application to
minikube
. - Run the app.
- View application logs.
Guide
- start minikube with
minikube start
- this will create and run a docker container called
minikube
- this will create and run a docker container called
minikube dashboard
Create a Deployment
Pod
- A Kubernetes Pod is a group of one or more Containers, tied together for the purposes of administration and networking.
- each container is basically based on an image
Deployment
- A Kubernetes Deployment checks on the health of your Pod and restarts the Pod’s Container if it terminates.
- You describe a desired state in a Deployment, and the Deployment Controller changes the actual state to the desired state at a controlled rate.
- Deployments are the recommended way to manage the creation and scaling of Pods
Objective
Create a deployment for a pod
use
kubectl
to look around the setup
Guide
Use the
kubectl create
command to create a Deployment that manages a Pod.- The Pod runs a Container based on the provided Docker image.
- in this example, a pod has only one container
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kubectl create deployment hello-node --image=k8s.gcr.io/echoserver:1.4
View the Deployment:
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kubectl get deployments
The output is similar to:
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2NAME READY UP-TO-DATE AVAILABLE AGE
hello-node 1/1 1 1 1mView the Pod:
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kubectl get pods
- which you will see the containers in the pod
View cluster events:
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kubectl get events
View the
kubectl
configuration:1
kubectl config view
Create a Service
Service
An abstract way to expose an application running on a set of Pods as a network service.
Kubernetes gives Pods their own IP addresses and a single DNS name for a set of Pods, and can load-balance across them
Note
- By default, the Pod is only accessible by its internal IP address within the Kubernetes cluster. To make the
hello-node
Container accessible from outside the Kubernetes virtual network, you have to expose the Pod as a Kubernetes Service.- this is similar to docker containers
Objective
- Create a service from a Deployment (which contains Pods)
- Use the service
Guide
Expose the Pod by exposing its Deployment
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kubectl expose deployment hello-node --type=LoadBalancer --port=8080
where:
exposing the deployment makes it a network service
--type=LoadBalancer
. On minikube, theLoadBalancer
type makes the Service accessible through theminikube service
command.- On cloud providers that support load balancers, an external IP address would be provisioned to access the Service.
View the Service you just created
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kubectl get services
Run the following command to use the service
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minikube service hello-node
Enabling Addons
Addons
- Add-ons extend the functionality of Kubernetes.
- Some of them are third party projects that provide functionality required by Kubernetes.
Objective
- View currently available add-ons
- Enable an add-on
- Disable an add-on
Guide
List the currently supported addons:
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minikube addons list
The output is similar to:
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17addon-manager: enabled
dashboard: enabled
default-storageclass: enabled
efk: disabled
freshpod: disabled
gvisor: disabled
helm-tiller: disabled
ingress: disabled
ingress-dns: disabled
logviewer: disabled
metrics-server: disabled
nvidia-driver-installer: disabled
nvidia-gpu-device-plugin: disabled
registry: disabled
registry-creds: disabled
storage-provisioner: enabled
storage-provisioner-gluster: disabledEnable an addon, for example,
metrics-server
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minikube addons enable metrics-server
The output is similar to:
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metrics-server was successfully enabled
View the Pod and Service you just created:
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kubectl get pod,svc -n kube-system
Disable
metrics-server
:1
minikube addons disable metrics-server
The output is similar to:
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metrics-server was successfully disabled
Clean Up
Objective
remove the
Service
you createdremove the
Deployment
you created- this will also remove the
Pods
under that deployment
- this will also remove the
optionally, stop and remove minikube VM
Guide
Clean up the resources you created in your cluster:
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2kubectl delete service hello-node
kubectl delete deployment hello-nodeOptionally, stop the Minikube virtual machine (docker container)
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minikube stop
Optionally, delete the Minikube VM (docker container):
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minikube delete
Minikube to Kubernetes
Reminder
Recall that a cluster contains the following:
![]()
where:
- The Master is responsible for managing the cluster.
- A Node is a VM or a physical computer that serves as a worker machine in a Kubernetes cluster (e.g. a running docker container)
- The nodes communicate with the master using the Kubernetes API
Pod vs Node
![]()
where:
- A Pod always runs on a Node.
- Pods are the atomic unit on the Kubernetes platform
- A Node can have multiple pods, and the Kubernetes master automatically handles scheduling the pods across the Nodes in the cluster.
Create a Cluster
Basically, we have done this with the minikube part - minikube itself is a node (since it is a docker container)!
For Example
Start minikube:
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minikube start
View it as a node:
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kubectl get nodes
gives you:
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2NAME STATUS ROLES AGE VERSION
minikube Ready control-plane,master 3m1s v1.20.2
Deploy an App
Once you have a running Kubernetes cluster (at least one node), you can deploy your containerized applications on top of it.
To do so, you create a Kubernetes Deployment configuration.
Reminder
- The Deployment instructs Kubernetes how to create and update instances of your application.
- You can create and manage a Deployment by using the Kubernetes command line interface,
kubectl
- When you created a Deployment, Kubernetes created a automatically Pod to host your application instance.
Deploying an App Basically does this
where:
- when you create a Deployment, you’ll need to specify the container image for your application and the number of replicas that you want to run.
Objective
- Deploy an app based on the
minikube
node- the app is created using a container image
Guide
.Make sure you have at least one node running. For example,
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minikube start
Deploy the app with the image
gcr.io/google-samples/kubernetes-bootcamp:v1
into the cluster1
kubectl create deployment kubernetes-bootcamp --image=gcr.io/google-samples/kubernetes-bootcamp:v1
where:
- if it is a docker image, you can just specify the name without the URL
- When you created a Deployment, Kubernetes created a Pod to host your application instance.
To see the state of the deployment, use
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kubectl get deployments
Reminder
- Pods that are running inside Kubernetes are running on a private, isolated network. By default they are visible from other pods and services within the same kubernetes cluster, but not outside that network.
- When we use
kubectl
, we’re interacting through an API endpoint to communicate with our application.
Therefore, to interact with Pods through
kubectl
API, one way to do it will be:- Create a
Proxy
withkubectl proxy
- this will basically start listening on port
8001
Use
Http
request to use/interact the service listening on8001
:1
curl http://localhost:8001/version
Note
- In order for the new deployment to be accessible without using the Proxy, a Service is required which will be explained in the next modules.
Exploring Your App
First, get the main concepts out of the way. The main picture in mind will be:
The picture in mind will be:
![](D:\jasonyux-Blog\Hexo\source\_posts\Kubernetes-Manual\Snipaste_2021-02-13_22-04-07.png)
Kubernetes Pods
A Pod is a Kubernetes abstraction that represents a group of one or more application containers (such as Docker), and some shared resources for those containers.
- For example, a Pod might include both the container with your Node.js app as well as a different container that feeds the data to be published by the Node.js webserver.
Pods are the atomic unit on the Kubernetes platform. When we create a Deployment on Kubernetes, that Deployment:
- creates Pods
- create containers inside Pods
(as opposed to creating containers directly).
Each Pod is tied to the Node where it is scheduled, and remains there until termination (according to restart policy) or deletion. In case of a Node failure, identical Pods are scheduled on other available Nodes in the cluster.
Node
- A Pod always runs on a Node.
- A Node is a worker machine in Kubernetes and may be either a virtual or a physical machine.
- Each Node is managed by the Master.
- the Kubernetes master automatically handles scheduling the pods across the Nodes in the cluster
- Every Kubernetes Node runs at least:
Kubelet
, a process responsible for communication between the Kubernetes Master and the Node.- A container runtime (like
Docker
) responsible for pulling the container image from a registry (for Pods), unpacking the container, and running the application.
Objective
- Look at the configuration of
pods
- Interact with containers inside a pod
Guide
We’ll use the
kubectl get
command and look for existing Podsview what containers are inside that Pod with
kubectl describe pods
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19Name: kubernetes-bootcamp-57978f5f5d-5j5rg
Namespace: default
Priority: 0
Node: minikube/192.168.49.2
Start Time: Sat, 13 Feb 2021 19:25:10 +0800
Labels: app=kubernetes-bootcamp
pod-template-hash=57978f5f5d
Annotations: <none>
Status: Running
IP: 172.17.0.2
IPs:
IP: 172.17.0.2
Controlled By: ReplicaSet/kubernetes-bootcamp-57978f5f5d
Containers:
kubernetes-bootcamp:
Container ID: docker://72b74c5cfa8e21a4cf996c8c6caa4a32b27d2749adc4a66f803d2d0af99163ea
Image: gcr.io/google-samples/kubernetes-bootcamp:v1
Image ID: docker-pullable://gcr.io/google-samples/kubernetes-
// other logs omittedwe see that it shows information such as:
- address, the ports used
- a list of events related to the lifecycle of the Pod.
- etc.
Note
the
describe
command can be used to get detailed information about most of the kubernetes primitives: node, pods, deployments.for example:
kubectl describe deployments
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28Name: kubernetes-bootcamp
Namespace: default
CreationTimestamp: Sat, 13 Feb 2021 19:25:10 +0800
Labels: app=kubernetes-bootcamp
Annotations: deployment.kubernetes.io/revision: 1
Selector: app=kubernetes-bootcamp
Replicas: 1 desired | 1 updated | 1 total | 1 available | 0 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 25% max unavailable, 25% max surge
Pod Template:
Labels: app=kubernetes-bootcamp
Containers:
kubernetes-bootcamp:
Image: gcr.io/google-samples/kubernetes-bootcamp:v1
Port: <none>
Host Port: <none>
Environment: <none>
Mounts: <none>
Volumes: <none>
Conditions:
Type Status Reason
---- ------ ------
Available True MinimumReplicasAvailable
Progressing True NewReplicaSetAvailable
OldReplicaSets: <none>
NewReplicaSet: kubernetes-bootcamp-57978f5f5d (1/1 replicas created)
Events: <none>
Now, to expose the container/app, you need to create a
proxy
, since Pods are isolated:1
kubectl proxy
- which will start listening on
8001
then, in a new terminal, use
kubectl
as the interface to communicate with thePod
:first, you need to get the name of pod:
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export POD_NAME=$(kubectl get pods -o go-template --template '{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}')
then, you can use it:
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curl http://localhost:8001/api/v1/namespaces/default/pods/$POD_NAME/proxy/
- which will start listening on
Anything that the application would normally send to
STDOUT
becomes logs for the container within the Pod.1
kubectl logs $POD_NAME
Lastly, we can execute commands directly on the container once the Pod is up and running with the
exec
command with name of the Pod as a parameter.1
kubectl exec $POD_NAME -- env
to do this interactively, use:
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kubectl exec -ti $POD_NAME -- bash
and now we are inside the container/Pod!
Note
- this step does not technically need a
proxy
running
- this step does not technically need a
To exit, use
exit
Expose Your App
Services and Labels
- A
Service
routes traffic across a set of Pods. Services are the abstraction that allow pods to die and replicate in Kubernetes without impacting your application.
- remember, each Pod in a Kubernetes cluster has a unique IP address. So this
Service
abstraction can be used to reconcile that- A
Service
is defined using YAML or JSON, and it targets a set of Pods by matching them using labels and selectors, a grouping primitive that allows logical operation on objects in Kubernetes.![]()
Overview of Services/Replica Set
- When a worker node dies, the Pods running on the Node are also lost. A
ReplicaSet
might then dynamically drive the cluster back to desired state via creation of new Pods to keep your application running.- In genera;
Services
allow your applications to receive traffic. Services can be exposed in different ways by specifying atype
in theServiceSpec
:
ClusterIP
(default) - Exposes the Service on an internal IP in the cluster. This type makes the Service only reachable from within the cluster.NodePort
- Exposes the Service on the same port of each selected Node in the cluster using NAT. Makes a Service accessible from outside the cluster using<NodeIP>:<NodePort>
. Superset of ClusterIP.LoadBalancer
- Creates an external load balancer in the current cloud (if supported) and assigns a fixed, external IP to the Service. Superset of NodePort.ExternalName
- Exposes the Service using an arbitrary name (specified byexternalName
in the spec) by returning a CNAME record with the name. No proxy is used. This type requires v1.7 or higher ofkube-dns
.
Objectives
- Expose a deployment to become a
Service
- View and change the
labels
of a Pod - Delete a
Service
Guides
First,we can see what services we have already:
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3jasonyux@XY-Laptop /code $ kubectl get services
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 9dThen, we want to create a Service and expose it to traffic with
kubectl expose
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6jasonyux@XY-Laptop /code $ kubectl expose deployment/kubernetes-bootcamp --type="NodePort" --port 8080
service/kubernetes-bootcamp exposed
jasonyux@XY-Laptop /code $ kubectl get services
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 9d
kubernetes-bootcamp NodePort 10.105.181.115 <none> 8080:31364/TCP 6swhere:
- external-IP of the node would be the IP of the Node itself. (which you can find out with
kubectl describe nodes
) - the
Deployment
also created automatically a label for our Pod.
- external-IP of the node would be the IP of the Node itself. (which you can find out with
Now, to see the labels of the Pod, use
describe
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6jasonyux@XY-Laptop /code :( $ kubectl describe deployment
Name: kubernetes-bootcamp
Namespace: default
CreationTimestamp: Sat, 13 Feb 2021 19:25:10 +0800
Labels: app=kubernetes-bootcamp
// other logs omittedthen, we can get the
Pod
by its label1
kubectl get pods -l run=kubernetes-bootcamp
and get the selected
Pods
of a service by label:1
kubectl get services -l run=kubernetes-bootcamp
To change the label of a pod, use
label pod
.first, get the Pod’s name:
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3jasonyux@XY-Laptop /code :( $ export POD_NAME=$(kubectl get pods -o go-template --template '{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}')
jasonyux@XY-Laptop /code $ echo Name of the Pod: $POD_NAME
Name of the Pod: kubernetes-bootcamp-57978f5f5d-5j5rgchange the
Pod
‘s name1
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9jasonyux@XY-Laptop /code $ kubectl describe pods
Name: kubernetes-bootcamp-57978f5f5d-5j5rg
Namespace: default
Priority: 0
Node: minikube/192.168.49.2
Start Time: Sat, 13 Feb 2021 19:25:10 +0800
Labels: app=v1
pod-template-hash=57978f5f5d
// other logs omittedNow, you can get the information by the new label:
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3jasonyux@XY-Laptop /code $ kubectl get pods -l app=v1
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-57978f5f5d-5j5rg 1/1 Running 1 9d
To delete services, you can also use its label/selector:
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kubectl delete service -l run=kubernetes-bootcamp
then, it is no longer exposed, but it is still running. This means you can still do:
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kubectl exec -ti $POD_NAME curl localhost:8080
Scaling an Application
Scaling
Scaling is accomplished by changing the number of replicas in a Deployment.
Scaling out a Deployment will:
- ensure new Pods are created and scheduled to Nodes with available resources.
- increase the number of Pods to the new desired state.
![]()
Reminder: Replica Set
- When a worker node dies, the Pods running on the Node are also lost. A
ReplicaSet
might then dynamically drive the cluster back to desired state via creation of new Pods to keep your application running.- A
ReplicaSet
is defined with fields, including a selector that specifies how to identify Pods it can acquire, a number of replicas indicating how many Pods it should be maintaining, and a pod template specifying the data of new Pods it should create to meet the number of replicas criteria.
- then, a
ReplicaSet
then fulfills its purpose by creating and deleting Pods as needed to reach the desired number.
Note
- Running multiple instances of an application will require a way to distribute the traffic to all of them.
Services
have an integrated load-balancer that will distribute network traffic to all Pods of an exposed Deployment.
Objective
- Scale your application/deployment using
kubectl scale
- Verify that the load-balancer is working automatically by communicating with the
Service
Guide
First, inspect the current state (deployments/replica set). You will see that:
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6jasonyux@XY-Laptop /code $ kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
kubernetes-bootcamp 1/1 1 1 15d
jasonyux@XY-Laptop /code $ kubectl get rs
NAME DESIRED CURRENT READY AGE
kubernetes-bootcamp-57978f5f5d 1 1 1 15dwhere, for
deployments
:- NAME lists the names of the Deployments in the cluster.
- READY shows the ratio of CURRENT/DESIRED replicas
- UP-TO-DATE displays the number of replicas that have been updated to achieve the desired state.
- AVAILABLE displays how many replicas of the application are available to your users.
- AGE displays the amount of time that the application has been running.
for
replica-set
:- DESIRED displays the desired number of replicas of the application, which you define when you create the Deployment. This is the desired state.
- CURRENT displays how many replicas are currently running.
Now, you can scale your deployment to
4
replicas:1
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5jasonyux@XY-Laptop /code $ kubectl scale deployment/kubernetes-bootcamp --replicas=4
deployment.apps/kubernetes-bootcamp scaled
jasonyux@XY-Laptop /code $ kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
kubernetes-bootcamp 4/4 4 4 15dInspect the scaled Pods in your deployment:
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6jasonyux@XY-Laptop /code $ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-57978f5f5d-9vtkx 1/1 Running 0 2m37s
kubernetes-bootcamp-57978f5f5d-jgqnt 1/1 Running 0 2m37s
kubernetes-bootcamp-57978f5f5d-lcg4t 1/1 Running 0 2m38s
kubernetes-bootcamp-57978f5f5d-tg497 1/1 Running 1 6d1hwhere you see that there are 4 Pods now, with different IP addresses.
You can also see all changes in the
deployment
log1
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15jasonyux@XY-Laptop /code $ kubectl describe deployments/kubernetes-bootcamp
Name: kubernetes-bootcamp
Namespace: default
CreationTimestamp: Sat, 13 Feb 2021 19:25:10 +0800
Labels: app=kubernetes-bootcamp
Annotations: deployment.kubernetes.io/revision: 1
Selector: app=kubernetes-bootcamp
Replicas: 4 desired | 4 updated | 4 total | 4 available | 0 unavailable
// some log omitted here
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 3m5s deployment-controller Scaled up replica set kubernetes-bootcamp-57978f5f5d to 4
Normal ScalingReplicaSet 2m17s deployment-controller Scaled up replica set kubernetes-bootcamp-57978f5f5d to 6
Normal ScalingReplicaSet 2m13s deployment-controller Scaled down replica set kubernetes-bootcamp-57978f5f5d to 4To find out the exposed IP and Port we can use the
describe service
, and then communicate with the deployments using the IP/Port.first, we look at the
Service
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17jasonyux@XY-Laptop /code $ kubectl describe services/kubernetes-bootcamp
Name: kubernetes-bootcamp
Namespace: default
Labels: app=kubernetes-bootcamp
Annotations: <none>
Selector: app=kubernetes-bootcamp
Type: NodePort
IP Families: <none>
IP: 10.105.181.115
IPs: 10.105.181.115
Port: <unset> 8080/TCP
TargetPort: 8080/TCP
NodePort: <unset> 31364/TCP
Endpoints: 172.17.0.3:8080,172.17.0.5:8080,172.17.0.6:8080 + 1 more...
Session Affinity: None
External Traffic Policy: Cluster
Events: <none>which is specified the IP and (Node) Port
now, again some handy renaming to environment variable
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2export NODE_PORT=$(kubectl get services/kubernetes-bootcamp -o go-template='{{(index .spec.ports 0).nodePort}}')
echo NODE_PORT=$NODE_PORTlastly, communicate:
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curl $(minikube ip):$NODE_PORT
where:
- We hit a different Pod with every request. This demonstrates that the load-balancing is working.
To scale down, use the same command:
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kubectl scale deployments/kubernetes-bootcamp --replicas=2
Performing a Rolling Update
Users expect applications to be available all the time and developers are expected to deploy new versions of them several times a day. In Kubernetes this is done with rolling updates.
Rolling Update
- Rolling updates allow Deployments’ update to take place with zero downtime by incrementally updating Pods instances with new ones. The new Pods will be scheduled on Nodes with available resources.
- By default, the maximum number of Pods that can be unavailable during the update and the maximum number of new Pods that can be created, is one.
- Both options can be configured to either numbers or percentages (of Pods).
Note
- In Kubernetes, updates are versioned and any Deployment update can be reverted to a previous (stable) version.
- Of course, in order to ensure high availability, you need more than one running Pods.
Objective
- Perform an update to your
deployment
by changing the application image - Check the rolling update status
- Revert back to previous update
Goal
Let’s begin with a
deployment
of 4 Pods1
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9jasonyux@XY-Laptop /code $ kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
kubernetes-bootcamp 4/4 4 4 15d
jasonyux@XY-Laptop /code $ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-57978f5f5d-9vtkx 1/1 Running 0 25m
kubernetes-bootcamp-57978f5f5d-jgqnt 1/1 Running 0 25m
kubernetes-bootcamp-57978f5f5d-lcg4t 1/1 Running 0 25m
kubernetes-bootcamp-57978f5f5d-vg7dt 1/1 Running 0 41sTo update the image of the application to version 2, use the
set image
command, followed by thekubectl set image <deployment_name> <container_name>:<image_name>
:first to see current image:
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10jasonyux@XY-Laptop /code $ kubectl describe pods
Name: kubernetes-bootcamp-57978f5f5d-vg7dt
Namespace: default
Priority: 0
Node: minikube/192.168.49.2
Start Time: Sun, 28 Feb 2021 23:21:05 +0800
Labels: app=kubernetes-bootcamp
pod-template-hash=57978f5f5d
// some logs omitted
Image: gcr.io/google-samples/kubernetes-bootcamp:v1then, to set the new state:
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4jasonyux@XY-Laptop /code $ kubectl set image deployments/kubernetes-bootcamp kubernetes-bootcamp=jocatalin/kubernetes-bootcamp
:v2
deployment.apps/kubernetes-bootcamp image updated
jasonyux@XY-Laptop /code $
Now, as an intermediate state, you might see:
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7jasonyux@XY-Laptop /code $ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-57978f5f5d-lcg4t 0/1 Terminating 0 31m
kubernetes-bootcamp-769746fd4-bgt2r 1/1 Running 0 50s
kubernetes-bootcamp-769746fd4-dggf8 1/1 Running 0 49s
kubernetes-bootcamp-769746fd4-g4k4f 1/1 Running 0 64s
kubernetes-bootcamp-769746fd4-l5mb4 1/1 Running 0 64sAgain, to verify that it is working, you can find out the exposed IP and Port we can use
describe service
, then get thenode-port
andip
and try to communicate usingcurl
- this is basically the same procedure as previous section
Additionally, updates can be confirmed with
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2jasonyux@XY-Laptop /code $ kubectl rollout status deployments/kubernetes-bootcamp
deployment "kubernetes-bootcamp" successfully rolled outso that now, the
image
field will be updated:1
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17jasonyux@XY-Laptop /code $ kubectl describe pods
Name: kubernetes-bootcamp-769746fd4-bgt2r
Namespace: default
Priority: 0
Node: minikube/192.168.49.2
Start Time: Sun, 28 Feb 2021 23:27:35 +0800
Labels: app=kubernetes-bootcamp
pod-template-hash=769746fd4
Annotations: <none>
Status: Running
IP: 172.17.0.9
IPs:
IP: 172.17.0.9
Controlled By: ReplicaSet/kubernetes-bootcamp-769746fd4
Containers:
// some logs omitted
Image: jocatalin/kubernetes-bootcamp:v2However, if we have performed a wrong update, for example setting the
image
version tov10
which does not exist1
2jasonyux@XY-Laptop /code $ kubectl set image deployments/kubernetes-bootcamp kubernetes-bootcamp=gcr.io/google-samples/kubernetes-bootcamp:v10
deployment.apps/kubernetes-bootcamp image updatedthen:
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3jasonyux@XY-Laptop /code $ kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
kubernetes-bootcamp 3/4 2 3 15dwhere:
- basically one Pod is down because it has the wrong image/update
A
describe
command on the Pods should give more insights:1
kubectl describe pods
in this case:
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28jasonyux@XY-Laptop /code $ kubectl describe pods
Name: kubernetes-bootcamp-597654dbd-b7p2c
Namespace: default
Priority: 0
Node: minikube/192.168.49.2
Start Time: Sun, 28 Feb 2021 23:32:52 +0800
Labels: app=kubernetes-bootcamp
pod-template-hash=597654dbd
Annotations: <none>
Status: Pending
IP: 172.17.0.5
IPs:
IP: 172.17.0.5
Controlled By: ReplicaSet/kubernetes-bootcamp-597654dbd
Containers:
kubernetes-bootcamp:
Container ID:
Image: gcr.io/google-samples/kubernetes-bootcamp:v10
// some logs omitted
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 82s default-scheduler Successfully assigned default/kubernetes-bootcamp-597654dbd-b7p2c to minikube
Warning Failed 36s (x2 over 66s) kubelet Failed to pull image "gcr.io/google-samples/kubernetes-bootcamp:v10": rpc error: code = Unknown desc = Error response from daemon: Get https://gcr.io/v2/: net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
Warning Failed 36s (x2 over 66s) kubelet Error: ErrImagePull
Normal BackOff 21s (x2 over 66s) kubelet Back-off pulling image "gcr.io/google-samples/kubernetes-bootcamp:v10"
Warning Failed 21s (x2 over 66s) kubelet Error: ImagePullBackOff
Normal Pulling 8s (x3 over 81s) kubelet Pulling image "gcr.io/google-samples/kubernetes-bootcamp:v10"where we see that error in the
Events:
tag:Failed to pull image "gcr.io/google-samples/kubernetes-bootcamp:v10": rpc error: code = Unknown desc = Error response from daemon: Get https://gcr.io/v2/: net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
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7. To **revert/undo** the last update, you can do:
```bash
jasonyux@XY-Laptop /code $ kubectl rollout undo deployments/kubernetes-bootcamp
deployment.apps/kubernetes-bootcamp rolled back
where:
- technically, updates are versioned and you can revert to any previously know state of a Deployment.
List again the Pods to confirm:
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6jasonyux@XY-Laptop /code $ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-769746fd4-4sllf 1/1 Running 0 89s
kubernetes-bootcamp-769746fd4-bgt2r 1/1 Running 0 10m
kubernetes-bootcamp-769746fd4-dggf8 1/1 Running 0 10m
kubernetes-bootcamp-769746fd4-l5mb4 1/1 Running 0 11m