Month: November 2018

This Kubernetes deployment tutorial guide will explain the key concepts in a Kubernetes YAML specification with an Nginx example deployment.

Introduction:

In Kubernetes, pods are the basic units that get deployed in the cluster. Kubernetes deployment is an abstraction layer for the pods. The main purpose of the deployment object is to maintain the resources declared in the deployment configuration in its desired state. A deployment configuration can be of YAML or JSON format.

Key Things To Understand

1. A Deployment can schedule multiple pods. A pod as a unit cannot scale by itself.
2. A Deployment represents a single purpose with a group of PODs.
3. A single POD can have multiple containers and these containers inside a single POD shares the same IP and can talk to each other using localhost address.
4. To access a Deployment with one or many PODs, you need a Kubernetes Service endpoint mapped to the deployment using labels and selectors.
5. A deployment should have only stateless services. Any application that requires state management should be deployed as a Kubernetes StatefulSet.

Deployment YAML:

Kubernetes deployment Yaml contains the following main specifications.

{
  "paths": [
    "/api",
    "/api/v1",
    "/apis",
    "/apis/",
    "/apis/admissionregistration.k8s.io",
    "/apis/admissionregistration.k8s.io/v1beta1",
    "/apis/apiextensions.k8s.io",
    "/apis/apiextensions.k8s.io/v1beta1",
    "/apis/apiregistration.k8s.io",
    "/apis/apiregistration.k8s.io/v1",
    "/apis/apiregistration.k8s.io/v1beta1",
    "/apis/apps",
    "/apis/apps/v1",
    "/apis/apps/v1beta1",
    "/apis/apps/v1beta2",
    "/apis/authentication.k8s.io",
    "/apis/authentication.k8s.io/v1",
    "/apis/authentication.k8s.io/v1beta1",
    "/apis/authorization.k8s.io",
    "/apis/authorization.k8s.io/v1",
    "/apis/authorization.k8s.io/v1beta1",
    "/apis/autoscaling",
    "/apis/autoscaling/v1",
    "/apis/autoscaling/v2beta1",
    "/apis/batch",
    "/apis/batch/v1",
    "/apis/batch/v1beta1",
    "/apis/certificates.k8s.io",
    "/apis/certificates.k8s.io/v1beta1",
    "/apis/cloud.google.com",
    "/apis/cloud.google.com/v1beta1",
    "/apis/extensions",
    "/apis/extensions/v1beta1",
    "/apis/metrics.k8s.io",
    "/apis/metrics.k8s.io/v1beta1",
    "/apis/networking.k8s.io",
    "/apis/networking.k8s.io/v1",
    "/apis/policy",
    "/apis/policy/v1beta1",
    "/apis/rbac.authorization.k8s.io",
    "/apis/rbac.authorization.k8s.io/v1",
    "/apis/rbac.authorization.k8s.io/v1beta1",
    "/apis/scalingpolicy.kope.io",
    "/apis/scalingpolicy.kope.io/v1alpha1",
    "/apis/storage.k8s.io",
    "/apis/storage.k8s.io/v1",
    "/apis/storage.k8s.io/v1beta1"
    ]
}

componentstatuses
configmaps
daemonsets
deployments
events
endpoints
horizontalpodautoscalers
ingress
jobs
limitranges
namespaces
nodes
pods
persistentvolumes
persistentvolumeclaims
resourcequotas
replicasets
replicationcontrollers
serviceaccounts
services

labels
name
namespace
annotations

metadata:
  name: resource-name
  namespace: deployment-demo
  labels:
    app: web
    platform: java
    release: 18.0
  annotations:
    monitoring: true
    prod: true

Spec has three important subfields.

1. Replicas: It will make sure the numbers of pods running all the time for the deployment. Example,

   spec:
     replicas: 3

2. Selector: It defines the labels that match the pods for the deployments to manage. Example,

   selector:
       matchLabels:
         app: nginx

3. Template: It has its own metadata and spec. Spec will have all the container information a pod should have. Container image info, port information, ENV variables, command arguments etc. Example,

   template:
       metadata:
         labels:
           app: nginx
       spec:
         containers:
           - image: nginx
             name: nginx

Kubernetes Example Deployment

Since we have looked at the basics let start with an example deployment. We will do the following in this section.

1. Create a namespace
2. Create a Nginx Deployment
3. Create a Nginx Service
4. Expose and access the Nginx Service

Note: Few of the operations we perform in this example can be performed with just kubectl and without a YAML Declaration. However, we are using the YAML specifications for all operations to understand it better.

Exercise Folder

To begin the exercise, create a folder names deployment-demo and cd into that folder. Create all the exercise files in this folder.

mkdir deployment-demo && cd deployment-demo

Create a Namespace

Let’s create a YAML named namespace.yaml file for creating the namespace.

apiVersion: v1
kind: Namespace
metadata:
  name: deployment-demo
  labels:
    apps: web-based
  annotations:
    type: demo

Use kubectl command to create the namespace.

kubectl create -f namespace.yaml

Equivalent kubectl command

kubectl create namespace deployment-demo

Assign Resource Quota To Namespace

Now let’s assign some resource quota limits to our newly created namespace. This will make sure the pods deployed in this namespace will not consume more system resources than mentioned in the resource quota.

Create a file named resourceQuota.yaml. Here is the resource quota YAML contents.

apiVersion: v1
kind: ResourceQuota
metadata:
  name: mem-cpu-quota
  namespace: deployment-demo
spec:
  hard:
    requests.cpu: "4"
    requests.memory: 8Gi
    limits.cpu: "8"
    limits.memory: 16Gi

Create the resource quota using the YAML.

kubectl create -f resourceQuota.yaml

Now, let’s describe the namespace to check if the resource quota has been applied to the deployment-demo namespace.

kubectl describe ns deployment-demo

The output should look like the following.

Name:         deployment-demo
Labels:       apps=web-based
Annotations:  type=demo
Status:       Active

Resource Quotas
 Name:            mem-cpu-quota
 Resource         Used  Hard
 --------         ---   ---
 limits.cpu       0     2
 limits.memory    0     2Gi
 requests.cpu     0     1
 requests.memory  0     1Gi

Create a Deployment

We will use the public Nginx image for this deployment.

Create a file named deployment.yaml and copy the following YAML to the file.

Note: This deployment YAML has minimal required information we discussed above. You can have more specification in the deployment YAML based on the requirement.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
  labels:
    app: nginx
  namespace: deployment-demo
  annotations:
    monitoring: "true"
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - image: nginx
        name: nginx
        ports:
        - containerPort: 80
        resources:
          limits:
            memory: "2Gi"
            cpu: "1000m"
          requests: 
            memory: "1Gi"
            cpu: "500m"

Under containers, we have defined its resource limits, requests and container port (one exposed in Dockerfile).

Create the deployment using kubectl

kubectl create -f deployment.yaml

Check the deployment

kubectl get deployments -n deployment-demo

Even though we have added minimal information, after deployment, Kubernetes will add more information to the deployment such as resourceVersion, uid, status etc.

You can check it by describing the deployment in YAML format using the kubectl command.

kubectl get deployment nginx -n deployment-demo  --output yaml

Create a Service and Expose The Deployment

Now that we have a running deployment, we will create a Kubernetes service of type NodePort ( 30500) pointing to the nginx deployment. Using NodePort you will be able to access the Nginx service on all the kubernetes node on port 30500.

Create a file named service.yaml and copy the following contents.

apiVersion: v1
kind: Service
metadata:
  labels:
    app: nginx
  name: nginx
  namespace: deployment-demo
spec:
  ports:
  - nodePort: 30500
    port: 80
    protocol: TCP
    targetPort: 80
  selector:
    app: nginx
  type: NodePort

Service is the best example for explaining labels and selectors. In this service, we have a selector with “app” = “nginx” label. Using this, the service will be able to match the pods in our nginx deployment as the deployment and the pods have the same label. So automatically all the requests coming to the nginx service will be sent to the nginx deployment.

Let’s create the service using kubectl command.

kubectl create -f service.yaml

You can view the service created using kubectl command.

kubectl get services  -n deployment-demo

Now, you will be able to access the nginx service on any one of the kubernetes node IP on port 30500

For example,

http://35.134.110.153:30500/