Kubernetes is complex and at first overwhelming if you never did something with it. In this post I want to focus on a simple deployment and putting some pieces (Pod, Deployment, ConfigMap, Ingress) together to get a better understanding for newbies.
I assume you are already familiar with the Kubernetes Basics and you have setup your own cluster.
Deploy an nginx container
As a developer you usually have your own application you want to deploy. However, for this post I go a different approach which maybe also more understanding from the people coming from operations. Let’s assume we have a static website we want to deploy:
<!DOCTYPE html>
<html>
<head>
<title>nginx-demo</title>
<style>
body {
width: 35em;
margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif;
background
}
</style>
</head>
<body>
<center>
<h1>Welcome to nginx-demo!</h1>
<p><img src="data:image/png;base64,iVBORw0KG......=" alt="my logo"/></p>
<p>Yeah it worked, you successfully deployed an nginx with a custom website.</p>
</center>
</body>
</html>
For this you need something which can serve the website, so we could use an nginx and deploy it as follows:
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-demo
namespace: nginx-demo
labels:
app: nginx-demo
spec:
replicas: 1
selector:
matchLabels:
app: nginx-demo
template:
metadata:
labels:
app: nginx-demo
spec:
containers:
- name: nginx
image: nginx:latest
imagePullPolicy: IfNotPresent
ports:
- containerPort: 80
This will deploy a single nginx pod:
$ kubectl create ns nginx-demo
$ kubectl apply -f ./nginx-demo.yaml
$ kubectl get pod -n nginx-demo
NAME READY STATUS RESTARTS AGE
nginx-demo-6dddfb4b45-pvc4k 1/1 Running 0 106s
You can then access the website using [kubectl proxy] to forward port 80 of the pod to port 5000 of your localhost:
$ kubectl port-forward $(kubectl get pod -n nginx-demo -o name --no-headers=true) -n nginx-demo 5000:80
Forwarding from 127.0.0.1:5000 -> 80
Forwarding from [::1]:5000 -> 80
Then in your browser you can access the port via https://localhost:5000, which serves the default nginx welcome page:
Use a ConfigMap to map your custom page
As next, you want to show the page mentioned above, rather than the default one. Here is where you can use a [ConfigMap]. The [ConfigMap] defines a file index.html with some custom HTML:
apiVersion: v1
kind: ConfigMap
metadata:
name: nginx-demo-indexhtml
namespace: nginx-demo
data:
index.html: |
<!DOCTYPE html>
<html>
<head>
<title>nginx-demo</title>
<style>
body {
width: 35em;
margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif;
background
}
</style>
</head>
<body>
<center>
<h1>Welcome to nginx-demo!</h1>
<p><img src="data:image/png;base64,iVBORw0KG......=" alt="my logo"/></p>
<p>Yeah it worked, you successfully deployed an nginx with a custom website.</p>
</center>
</body>
</html>
The index.html from the [ConfigMap] shall replace the default /usr/share/nginx/html/index.html within the container. This is done by mapping it into the container, by extending the nginx-demo.yaml with volumeMounts and volumes, telling kubernetes to map the file from withom zhe [ConfigMap] to the desired path in the pod:
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-demo
namespace: nginx-demo
labels:
app: nginx-demo
spec:
replicas: 1
selector:
matchLabels:
app: nginx-demo
template:
metadata:
labels:
app: nginx-demo
spec:
containers:
- name: nginx
image: nginx:latest
imagePullPolicy: IfNotPresent
ports:
- containerPort: 80
volumeMounts:
- mountPath: /usr/share/nginx/html/index.html
name: nginx-indexhtml-vol
subPath: index.html
volumes:
- ConfigMap:
defaultMode: 420
items:
- key: index.html
path: index.html
name: nginx-demo-indexhtml
name: nginx-indexhtml-volThis will restart the pod and then you issue again the same [kubectl proxy] command as above:
$ kubectl port-forward $(kubectl get pod -n nginx-demo -o name --no-headers=true) -n nginx-demo 5000:80
Forwarding from 127.0.0.1:5000 -> 80
Forwarding from [::1]:5000 -> 80
This should give you an idea of what a [ConfigMap] offers
Ingress
[kubectl proxy] works ok but it’s not how we want to access our website, we prefer something like https://nginx-demo.intra, Thus we need two things
-
expose the application as a [network service][Service]
kind: Service apiVersion: v1 metadata: name: nginx-demo-service namespace: nginx-demo spec: selector: app: nginx-demo ports: - port: 80 # Default port for image -
an [Ingress] which exposes HTTP and HTTPS routes from outside the cluster to [services][Service]
You must have an Ingress controller to satisfy an Ingress. Only creating an Ingress resource has no effect.