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| =Introduction=
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| =Containers=
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| This all started with VMWare where the total resource could be divided up to run more than one application on difference virtual machines. But VMWare required an OS on every machine and licenses in the case of Windows. They also needed managing, e.g. patching, Anti-virus and patching. Along came containers which shared the OS.
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| <br>
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| [[File:Containers Overview.png|500px]]
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| <br>
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|
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| =Docker=
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| ==Introduction==
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| Docker Inc. Docker is a company which gave the word technology for containers. They are now a company which provides services around the company.
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| <br>
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| <br>
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| Docker is Open source and known as Community Edition (CE). The company Docker releases an Enterprise Edition (EE).
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| <br>
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| The general approach is to
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| *Create an image (docker build)
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| *Store it in a registry (docker image push)
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| *Start a container from it (docker container run)
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| The differences between EE and CE are shown below
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| [[File:Docker Diffs.png|500px]]
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| ==Architecture==
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| Docker is made up of a docker engine and containers which are comprised of namespaces and control groups. Wiki defines namespaces as '''Namespaces are a feature of the Linux kernel that partitions kernel resources such that one set of processes sees one set of resources while another set of processes sees a different set of resources.'''
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| <br>
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| ===Docker Engine===
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| [[File:Docker engine.png|400px]]
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|
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| ===Namespace Types===
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| Within the Linux kernel, there are different types of namespaces. Each namespace has its own unique properties:
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| [[File:Docker namespace arch.png|400px]]
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| *A user namespace has its own set of user IDs and group IDs for assignment to processes. In particular, this means that a process can have root privilege within its user namespace without having it in other user namespaces.
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| *A process ID (PID) namespace assigns a set of PIDs to processes that are independent from the set of PIDs in other namespaces. The first process created in a new namespace has PID 1 and child processes are assigned subsequent PIDs. If a child process is created with its own PID namespace, it has PID 1 in that namespace as well as its PID in the parent process’ namespace. See below for an example.
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| *A network namespace has an independent network stack: its own private routing table, set of IP addresses, socket listing, connection tracking table, firewall, and other network‑related resources.
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| *A mount namespace has an independent list of mount points seen by the processes in the namespace. This means that you can mount and unmount filesystems in a mount namespace without affecting the host filesystem.
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| *An interprocess communication (IPC) namespace has its own IPC resources, for example POSIX message queues.
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| *A UNIX Time‑Sharing (UTS) namespace allows a single system to appear to have different host and domain names to different processes.
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| ===Control Groups===
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| A control group (cgroup) is a Linux kernel feature that limits, accounts for, and isolates the resource usage (CPU, memory, disk I/O, network, and so on) of a collection of processes.
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| <br>
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| Now we have namespace we need a way to control the resources across the namespaces. This is where cgroups come in.
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| <br>
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| [[File:Docker CGroup arch.png|400px]]
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| *Resource limits – You can configure a cgroup to limit how much of a particular resource (memory or CPU, for example) a process can use.
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| *Prioritization – You can control how much of a resource (CPU, disk, or network) a process can use compared to processes in another cgroup when there is resource contention.
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| *Accounting – Resource limits are monitored and reported at the cgroup level.
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| *Control – You can change the status (frozen, stopped, or restarted) of all processes in a cgroup with a single command.
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|
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| =Kubernetes=
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| Kubernetes came out of Google and Open Source. Greek for helmsman or k8s (Kates). Kubernetes is an orchestrator and can schedule, scale and update containers. There are alternatives like Docker Swarm
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| <br>
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| [[File:K8_Overview.png|500px]]
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| ==Architecture==
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| ===Overview===
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| Apps are put in a container, wrapped in a pod and deployment details. They are provisioned on a Node inside a K8s Clustoer<br>
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| [[File:K8 Arch.png|600px]]
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| ===Master===
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| In general these are a hosted services on the cloud but you can run them locally on a linux box.
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| *This is the front-end to the control plane
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| *It exposes a RESTFul API consuming JSON and Yaml
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| *We send manifests describing our apps to this
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| <br>
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| The Cluster Store for users with large changes often separate this
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| <br>
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| <br>
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| The controllers controls
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| *Node Controller
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| *Deployment controller
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| *Endpoints/EndpointSlice
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| <br>
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| The scheduler
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| *Watches for new work
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| *Assigns Work to the cluster nodes
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| <br>
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| [[File:K8 Master3.png|400px]]
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| ===Kubernetes Nodes===
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| Now its time for the Nodes. These are made up of three parts, the Kublet, Container runtime and the Kube Proxy<br>
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| [[File:K8 Nodes.png|300px]]
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| ====Kubelet====
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| The Kubelet is the Main Kubernetes agent it
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| *Registers node with the cluster
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| *Watches API Server for work tasks (Pods)
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| *Executes Pods
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| *Reports to the master
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|
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| ====Container Runtime====
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| *Can be Docker
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| *Pluggable via Container Runtime Interface (CRI)
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| *Generally is Docker or containerd, other like gVisor and katacontainers exist
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| *Does the stop and starting of containers
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| ====Kube Proxy====
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| *The Networking Component
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| *Does light-weight load balancing
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|
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| ===Declarative Model/Desired State===
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| We describe what we want the cluster to look like but we do not care how it happens. Kubernetes constantly checks the desired state matches the observed state.
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| ===Pods===
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| A pod is a shared execution environment and can container one or more containers. It is the Pod which has a unique IP. Containers within the same pod must allocate unique ports if they are to talk to each other or the outside world. The same for volumes etc.When scaling you scale Pods not Containers.<br>
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| [[File:K8 Pods.png|400px]]
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| <br>
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| Multi container Pods are for two different but complimentary containers which need to be aligned. An example of this might be a service mesh. For example the mesh container could be responsible for encryption or decryption. '''Note''' Deployment of Pods is atomic
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| <br>
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| [[File:K8 Mesh2.png|400px]]
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| <br>
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| Pods provide
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| *Annotations
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| *Labels
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| *Policies
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| *Resources
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| *Co-scheduling of contianers
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| and other Metadata.
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| ===Kubernetes Service Objects===
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| As mentioned the IP address are provided for each Pod. However Pods die, we scales up and down and it would not be practical to use them so Kurbenetes provides the Service object which is describe in the deploymennt. With the use of labels the Service object knows which pods to send traffic to. By either removing labels from the pod the objects can be match generically.
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| <br>
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| [[File:K8 Svc1.png|400px]]
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| <br>
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| In the example below both 1.3 and 1.4 will be matched of the Pods. Equally we could add a version to the service object and the unmatched version would not be used.
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| <br>
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| [[File:K8 Svc2.png|400px]]
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| Service objects
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| *Only Send traffic to healthy Pods
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| *Can do session affinity (Sending of subsequent requests to the same Pod)
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| *Can send traffic to endpoints outside of the cluster
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| *Can do TCP and UDP
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| ===Kubernetes API Server===
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| This is the API which exposes and RESTFul API. It exposes the various objects handles the requests. The objects are broken up into various sub categories. We use the command line kubectl to control this.
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| [[File:K8 API.png|500px]]
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| ==Installing Ubuntu==
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| This was really easy. Had to use Firefox to get the dashboard to work on https://127.0.0.1:10443. Need to review how to get it to work on Chrome.
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| <syntaxhighlight lang="bash">
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| sudo snap install microk8s --classic
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| sudo usermod -a -G microk8s $USER
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| sudo chown -f -R $USER ~/.kube
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| su - $USER
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| microk8s status --wait-ready
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| microk8s enable dashboard dns ingress
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| microk8s kubectl get all --all-namespaces
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| microk8s dashboard-proxy
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| </syntaxhighlight>
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| To be able to use the dashboard on chrome you need to go to chrome://flags/#allow-insecure-localhost and enable Allow invalid certificates for resources loaded from localhost. Firefox works by default.
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|
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| ==Deploying Pods==
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| ===Introduction===
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| We do this by
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| *Creating App Code
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| *Create an image
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| *Store in a repo
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| *Define in a manifest
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| *Post to the API Server
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| ===Example===
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| ====Creating App Code====
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| Clone the App Code
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| <syntaxhighlight lang="bash">
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| git clone https://github.com/nigelpoulton/getting-started-k8s.git
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| </syntaxhighlight>
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| ====Create an Image====
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| Easy pezzy lemon squeezy. Where nigelpulton is your own Docker hub account/repository
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| <syntaxhighlight lang="bash">
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| cd getting-started-k8s/App
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| docker image build -t nigelpulton/getting-started-k8s:1.0 .
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| </syntaxhighlight>
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| ====Store in repo====
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| Now push the image to your docker hub account.
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| <syntaxhighlight lang="bash">
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| docker image push nigelpoulton/getting-started-k8s:1.0
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| </syntaxhighlight>
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| ====Define in a manifest====
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| We can define this in either Yaml or Json. I used yq eval -j to convert mine but it does say kubectl convert should work. I am using microk8s and it said it did not work.
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| <br>
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| <syntaxhighlight lang="yaml">
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| apiVersion: v1
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| kind: Pod
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| metadata:
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| name: hello-pod
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| labels:
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| app: web
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| spec:
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| containers:
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| - name: web-ctr
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| image: nigelpulton/getting-started-k8s:1.0
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| ports:
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| - containerPort: 8080
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| </syntaxhighlight>
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| <br>
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| And the json version
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| <syntaxhighlight lang="json">
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| {
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| "apiVersion": "v1",
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| "kind": "Pod",
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| "metadata": {
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| "name": "hello-pod",
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| "labels": {
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| "app": "web"
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| }
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| },
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| "spec": {
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| "containers": [
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| {
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| "name": "web-ctr",
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| "image": "nigelpulton/getting-started-k8s:1.0",
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| "ports": [
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| {
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| "containerPort": 8080
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| }
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| ]
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| }
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| ]
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| }
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| }
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| </syntaxhighlight>
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| The "Kind" and "apiVersion" refer to the object. The objects you can use are grouped into types. Here is some of the objects in the apps group.
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| <br>
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| [[File:K8 Manifest Types1.png|300px]]
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| The default image tag by default will use the docker hub. You can add a prefix with the dns name if it is stored somewhere else.
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| ====Post to the API Server====
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| You can post the manifest to the cluster with
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| <syntaxhighlight lang="bash">
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| cd Pods
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| kubectl apply -f pod.yml
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|
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| # Get the status
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| kubectl get pods --watch -o wide
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|
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| # Get All the Pod information
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| kubectl describe pods hello-pod
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| </syntaxhighlight>
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|
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| ===Example Cleanup===
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| To clean up the deployment we can either
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| <syntaxhighlight lang="bash">
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| # Delete by using delete and the manifest
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| kubectl delete -f pod.yml
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| # Or delete using the name
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| kubectl delete pod hello-pod
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| </syntaxhighlight>
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|
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| ==Kubernetes Services==
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| The Service has a frontend and a backend.<br>
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| [[File:K8 Svc FrontEnd.png|400px]]
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| ===Frontend===
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| The frontend is
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| *Name
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| *IP
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| *Port
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| The IP on the frontend is called a ClusterIP and is assigned by Kubernetes. It is only for use within the cluster. The name is the name of the service and that is registered with DNS.
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| <br>
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| '''Every container in every pod can resolve service names'''
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| ===Backend===
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| Is a way for the service to know which pods to send track on to. The endpoint slice tracks the list of healthy Pod which match the services label selector.
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| ===Types of Service===
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| *LoadBalancer External access via cloud load-balancer
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| *NodePrt External access via nodes
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| *ClusterIP (default) internal cluster connectivity
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| ===Creating a Services===
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| We can create service in two ways
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| *Imperatively
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| *Declaratively
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| ====Imperatively====
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| With imperative we can simply use the kubectl.
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| <syntaxhighlight lang="bash">
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| kubectl expose pod hello-pod --name=hello-svc --target-port=8080 --type=NodePort
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|
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| microk8s kubectl get svc
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| >NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
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| >kubernetes ClusterIP 10.152.183.1 <none> 443/TCP 21h
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| >hello-svc NodePort 10.152.183.147 <none> 8080:30737/TCP 11s
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| </syntaxhighlight>
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| From there we can get to the service using the node port which is the outbound port shown for the service. In our case this is 30737. So going to the ip of the machine and port should show the service. e.g. htttp://192.xxx.xxx.1.70:30737. Node ports are allocated by Kubernetes between 32000 and 32767
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|
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| ====Declaratively====
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| Here is the yaml file to create the above service. Note I put the word name inside of app for the selector which resulted in the service having no endpoint.
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| <syntaxhighlight lang="yaml">
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| apiVersion: v1
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| kind: Service
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| metadata:
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| name: ps-nodeport
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| spec:
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| type: NodePort
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| ports:
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| - port: 80
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| targetPort: 8080
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| nodePort: 31111
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| protocol: TCP
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| selector:
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| app: web
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| </syntaxhighlight>
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|
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| And here is a picture to explain the ports.
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| <br>
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| [[File:K8 SVC Ports.png|300px]]
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| <br>
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| *31111 is the port for external access
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| *80 is the port the cluster is listening on
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| *8080 is the port exposed by the pod and the defined in the docker container
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| We can check we have the right name (label) in the service with the command
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| <syntaxhighlight lang="bash">
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| kubectl get pods --show-labels
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| >NAME READY STATUS RESTARTS AGE LABELS
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| >hello-pod 1/1 Running 0 79m app=web
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| </syntaxhighlight>
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|
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| ====Clean up====
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| Deleting service can be done with
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| <syntaxhighlight lang="bash">
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| kubectl delete svc hello-svc
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| </syntaxhighlight>
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| ==Deployments==
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| ===Introduction===
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| To deploy a solution we need
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| *Deployment (Updates and Rollbacks)
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| *Replication Set (Scalability, Reliability, Desired State)
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| *Pod (Scheduling and Execution)
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| *App (App code)
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| ===Rolling Updates and Rollbacks===
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| To update we simply provide a new version of the deployment. We can define how this happens e.g. wait 10 mins before OK. Kubernetes keeps the old pods to allow the user to reverse the deployment by using a previous version of the deployment. Here we see the rollback where the green pods are being replace by the original pods.
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| [[File:K8 Deploy Rollbacks.png|400px]]
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| ===Deployment Section===
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| The example below show a deployment and provides and overview. The labels in the deployment spec must match the label in the Pods spec. The always is for security and ensures the code not the local copy.<br>
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| [[File:K8 Deployment Example.png|600px]]
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| <br>
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| ===Full Example===
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| Here is a full example. There are many options under the strategy we can configure. In this example we have opted for
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| *minReadySeconds The amount of time to wait and see if container is working before proceeding
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| *maxUnavailable Number which should be available during update
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| *maxSurge The number it can exceed the desired amount by.
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| So in this example there will be 6 pods during the update and it will wait for 5 seconds and reduce back down to 5.
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| <syntaxhighlight lang="yaml">
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| apiVersion: apps/v1
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| kind: Deployment
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| metadata:
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| name: web-deploy
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| labels:
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| app: web
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| spec:
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| selector:
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| matchLabels:
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| app: web
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| replicas: 5
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| minReadySeconds: 5
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| strategy:
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| type: RollingUpdate
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| rollingUpdate:
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| maxUnavailable: 0
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| maxSurge: 1
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| template:
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| metadata:
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| labels:
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| app: web
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| spec:
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| terminationGracePeriodSeconds: 1
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| containers:
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| - name: hello-pod
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| image: nigelpoulton/getting-started-k8s:2.0
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| imagePullPolicy: Always
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| ports:
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| - containerPort: 8080
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| </syntaxhighlight>
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| ===Doing Update===
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| To perform an update we use the deploy command
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| <syntaxhighlight lang="bash">
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| #Do Deployment
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| kubectl apply -f deploy-complete.yml
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|
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| #Monitor the deploy progress with
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| kubectl get deploy
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|
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| #Monitor the replicate sets progress with
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| kubectl get rs
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| </syntaxhighlight>
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| ===Reversing the update===
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| As discussed the old replicates still reside with in kubernetes. We can see this by looking as the replication sets. We can reverse the update by
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| <syntaxhighlight lang="bash">
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| #Get the deployment history
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| kubectl rollout history deploy web-deploy
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|
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| >deployment.apps/web-deploy
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| >REVISION CHANGE-CAUSE
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| >1 <none>
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| >2 <none>
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|
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| #To reverse we just need to provide the revision to rollback to.
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| kubectl rollout undo deploy web-deploy --to-revision=1
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|
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| </syntaxhighlight>
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|
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| ===Monitoring Deployment===
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| We can see both the deploy and the replication sets with
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| <syntaxhighlight lang="bash">
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| kubectl get deploy
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| kubectl get rs
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| </syntaxhighlight>
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| We can use describe ep to see the endpoints for our configuration.
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| <syntaxhighlight lang="bash">
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| microk8s kubectl describe ep
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|
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| >Name: ps-nodeport
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| >Namespace: default
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| >Labels: <none>
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| >Annotations: endpoints.kubernetes.io/last-change-trigger-time: 2021-08->14T17:53:23+12:00
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| >Subsets:
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| > Addresses: 10.1.114.202
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| > NotReadyAddresses: <none>
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| > Ports:
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| > Name Port Protocol
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| > ---- ---- --------
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| > <unset> 8080 TCP
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| >
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| >Events: <none>
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| iwiseman@OLIVER:
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| </syntaxhighlight>
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|
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| ===Self Healing and Scaling===
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| We can delete pods and nodes and Kubernetes will fix the problem. This is known as self healing. We can manually deploy with more replicas to scale up and down. There is Horizontal Pod Autoscaler and Cluster Autoscaler as well.
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