Kubernetes HTTP Fileserver

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Kubernetes HTTP Fileserver
- Serving static files from inside a Docker Container
- Serving static files from a PersistentVolume (Recommended)

Kubernetes HTTP Fileserver

Serving static files from inside a Docker Container

Create a Dockerfile to work with the official NGINX Docker Container that will copy all the content from the download folder to the public directory of the NGINX server:

FROM nginx
COPY downloads/ /usr/share/nginx/html

Build the image and tag it for your Docker repository:

docker build -t my-docker-hub-account/http-fileserver-kubernetes .

(Optional) Test run your container:

docker run -d -p 8080:80 my-docker-hub-account/http-fileserver-kubernetes

You should now be able to access the files you stored inside the downloads folder via http://localhost:8080/dl/test.txt (assuming that you used the downloads folder from the repository, that contains a sub directory dl that contains a text file test.txt):

Push the Docker Image to Docker hub

docker login
docker push my-docker-hub-account/http-fileserver-kubernetes

Alternatively, do your build on the host system where you want to run the image - so the image is in local storage. This is a hacky solution that is not fully supported - if you don't want to push your image to the Docker Hub, you are supposed to use a local/personal registry for your Docker images. That feels a little bit much for my problem here - so I will proceed with this way.

Note: if you want to use the local image, you have to build the image on every Node server that you are using in Kubernetes and that might be used to spawn the pod. You also have to set the imagePullPolicy= Never (see YAML file in the next step)! This will make sure that Kubernetes will always use the image from local storage instead of trying to pull it from Docker Hub.

Creating the Kubernetes Deployment

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  creationTimestamp: null
  labels:
    service: http-fileserver
  name: http-fileserver
spec:
  replicas: 1
  strategy: {}
  template:
    metadata:
      creationTimestamp: null
      labels:
        service: http-fileserver
    spec:
      containers:
      - image: my-docker-hub-account/http-fileserver-kubernetes:latest
        imagePullPolicy: Always
        name: http-fileserver
        resources: {}
      restartPolicy: Always
status: {}

---

apiVersion: v1
kind: Service
metadata:
  creationTimestamp: null
  labels:
    service: http-fileserver
  name: http-fileserver
spec:
  ports:
    - name: http
      port: 80
  selector:
    service: http-fileserver
status:
  loadBalancer: {}

Alternatively use a simple pod, instead of a deployment:

kind: Pod
apiVersion: v1
metadata:
  name: http-fileserver
  labels:
    app: fileserver
spec:
  containers:
    - name: http-fileserver
      image: my-docker-hub-account/http-fileserver-kubernetes:latest
      imagePullPolicy: Always
      ports:
        - containerPort: 80

---

kind: Service
apiVersion: v1
metadata:
  name: http-fileserver
spec:
  selector:
    app: fileserver
  ports:
    - port: 80

You can run the deployment (or pod) by the Kubernetes command - see Kubernetes Ingress:

kubectl create -f http-fileserver.yaml

Serving static files from a PersistentVolume (Recommended)

If all you have to serve are a few text files, the above solution will be sufficient. But what if we are talking about a large quantity of files you want to make available over the internet? Adding your files to a persistent storage and linking it to all services that need to have access to it will be the way to go.

To accomplish this we need to do the following tasks:

Create a PersistentVolume that is backed by physical storage but is not associate with any Pod.
Create a PersistentVolumeClaim, which gets automatically bound to a suitable PersistentVolume.
Create a Pod that uses the PersistentVolumeClaim as storage.

Create a PersistentVolume

Let's start with creating a folder that is going to hold our files, e.g. /opt/filecontainer/dl, and a file to it that you want to serve:

mkdir /opt/filecontainer/dl
echo 'This is a test' > /opt/filecontainer/dl/index.txt

We will create a hostPath PersistentVolume. Kubernetes supports hostPath for development and testing on a single-node cluster. A hostPath PersistentVolume uses a file or directory on the Node to emulate network-attached storage (see Google Compute Engine persistent disk, an NFS share, or an Amazon Elastic Block Store volume instead if you are using the corresponding cloud solutions).

The configuration file for the hostPath PersistentVolume looks like this:

file-storage-pv.yaml

kind: PersistentVolume
apiVersion: v1
metadata:
  name: file-storage-volume
  labels:
    type: local
spec:
  storageClassName: manual
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/opt/filecontainer"

The configuration file specifies that the volume is at /opt/filecontainer on the cluster’s Node. The configuration also specifies a size of 3Gi and an access mode of ReadWriteOnce, which means the volume can be mounted as read-write by a single Node. It defines the StorageClass name manual for the PersistentVolume, which will be used to bind PersistentVolumeClaim requests to this PersistentVolume.

Create the PersistentVolume:

kubectl apply -f file-storage-pv.yaml
kubectl get pv file-storage-volume

The output shows that the PersistentVolume has a STATUS of Available.

Create a PersistentVolumeClaim

The next step is to create a PersistentVolumeClaim. Pods use PersistentVolumeClaims to request physical storage. In this exercise, you create a PersistentVolumeClaim that requests a volume of at least three gigs that can provide read-write access for at least one Node.

Here is the configuration file for the PersistentVolumeClaim:

file-storage-pvc.yaml

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: file-storage-claim
spec:
  storageClassName: manual
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 3Gi

After you create the PersistentVolumeClaim, the Kubernetes control plane looks for a PersistentVolume that satisfies the claim’s requirements. If the control plane finds a suitable PersistentVolume with the same StorageClass, it binds the claim to the volume.

kubectl apply -f file-storage-pvc.yaml
kubectl get pv file-storage-volume

Now the output shows a STATUS of Bound.

Create a Pod

The next step is to create a Pod that uses your PersistentVolumeClaim as a volume.

Here is the configuration file for the Pod:

file-storage-pod.yaml

kind: Pod
apiVersion: v1
metadata:
  name: file-storage
  labels:
    app: file-storage
spec:
  volumes:
    - name: file-storage-volume
      persistentVolumeClaim:
       claimName: file-storage-claim
  containers:
    - name: file-storage-container
      image: nginx
      ports:
        - containerPort: 80
          name: file-storage
      volumeMounts:
        - mountPath: "/usr/share/nginx/html"
          name: file-storage-volume

Create the Pod and verify that the Container in the Pod is running:

kubectl create -f file-storage-pod.yaml
kubectl exec -it file-storage -- /bin/bash

We can see that our /opt/filecontainer folder was successfully mounted to /usr/share/nginx/html !

We can also test if NGINX is running and serving our content by installing curl inside the container and checking if the file is available on localhost:

apt update
apt install curl
curl http://localhost/dl/index.txt

The file we created is being served by the NGINX web service!

Creating the Service

To access the pod we first have to create a service that point to it:

file-storage-service.yaml

apiVersion: v1
kind: Service
metadata:
  creationTimestamp: null
  labels:
    app: file-storage
  name: file-storage
spec:
  ports:
    - name: http
      port: 80
  selector:
    app: file-storage
status:
  loadBalancer: {}

Troubleshooting a Service

I am returning here after noticing that the Ingress, I am going to add in the next step, does not seem to work. We already tested that the pod we created is running, has the PersistentVolume mounted and is hosting our content - so maybe the service is not attached to the pod?

What happens if a Service does not seem to work? We can follow the Kubernetes Debug Guide to check where the issue lies.

We can start by checking if the pod we created can be found by it's label

kubectl get pods -l app=file-storage

Assuming you have another Pod that already consumes the Service by name you would get something like:

wget -O- file-storage
Resolving file-storage (file-storage)... failed: Name or service not known.
wget: unable to resolve host address ‘file-storage’

So the first thing to check is whether that Service actually exists:

kubectl get svc file-storage
NAME           TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)   AGE
file-storage   ClusterIP   10.102.5.116   <none>        80/TCP    14h

The Pod is available, the service is running, but we are not getting access to the service using the wget command. Also a curl file-storage:80/dl/test.txt fails - is there something wrong with the DNS resolution?

Trying to access the pod through the service works without a hitch, when using the Cluster IP address:

curl 10.102.5.116:80/dl/test.txt

I am turning a bit in circles now - the POD can be selected by the same label the SERVICE is using to find the service (app=file-storage). The service correctly uses the as ENDPOINT kubectl get endpoints file-storage (10.32.0.54:80) - we can verify that this IP is really the IP of our pod by running kubectl get pod file-storage -o wide.

If no endpoint is found for file-storage, you should check that the spec.selector field of your Service actually selects for metadata.labels values on your Pods. A common mistake is to have a typo or other error, such as the Service selecting for service: file-storage, but the Deployment specifying app: file-storage.

Both the pod and the service are working and the services is finding our pod - everything seems to be as it should be... onward with Troubleshooting the Ingress.

Adding it to our NGINX Ingress

To route traffic to our cluster we are using the NGINX Ingress - in theory we only have to add our service to the Ingress Configuration and assign it to a sub-URL that we want to use:

nginx-ingress.yaml

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: nginx-ingress
spec:
  rules:
  - http:
      paths:
        - path: /web
          backend:
            serviceName: web-service
            servicePort: 5678
        - path: /mobile
          backend:
            serviceName: mobile-service
            servicePort: 5678
        - path: /test
          backend:
            serviceName: test-service
            servicePort: 3000
        - path: /dl
          backend:
            serviceName: file-storage
            servicePort: 80

Note that we could use the annotation ingress.kubernetes.io/rewrite-target: / to rewrite all incoming traffic to root. That means that, even though you are able to access the file storage app on /dl the app will register this traffic relative to / instead.

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: nginx-ingress
  annotations:
    ingress.kubernetes.io/rewrite-target: /
    ...

We are now able to access the fileserver over the WAN IP address of your Kubernetes MASTER Server:

Deployment

We can now delete the Pod and rewrite it as a Kubernetes Deployment

file-storage-development.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: file-storage
  labels:
    app: file-storage
spec:
  selector:
    matchLabels:
      app: file-storage
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: file-storage
    spec:
      containers:
      - name: file-storage-container
        image: nginx
        ports:
        - containerPort: 80
          name: file-server
        volumeMounts:
          - mountPath: "/usr/share/nginx/html"
            name: file-storage-volume
        imagePullPolicy: Always
        resources: {}
      volumes:
        - name: file-storage-volume
          persistentVolumeClaim:
           claimName: file-storage-claim

Create the development and verify that the Pod is running:

kubectl create -f file-storage-development.yaml
kubectl get development file-storage
kubectl get pods

The pod should now be listed two blocks characters attached to the pod name - assigning it to your deployment and replicaset: e.g. file-storage-74bdcc99c4-bhfnb.

You can use the same troubleshooting we used before to check if the Pod is operational and connected to your service.

Troubleshooting the NGINX Ingress

There are many ways to troubleshoot the ingress-controller. The following are basic troubleshooting methods to obtain more information.

kubectl get ing -n default

Here I already found my first mistake, I renamed the ingress during development and an older version of it was not deleted, when I applied the updated config. But deleting the dupe did not solve the issue that the ingress does not seem to work.

kubectl describe ing nginx-ingress -n default

This command shows us if the service was bound correctly:

Rules:
  Host              Path  Backends
  ----              ----  --------
  my.domain.com  
                    /dl      file-storage:80 (<none>)

Everything looks fine - we can now go on to check the Ingress Controller logs:

kubectl get pods -n ingress-nginx
kubectl logs -f nginx-ingress-controller-797b884cbc-f5qdt -n ingress-nginx

In my case the pod can be referenced as nginx-ingress-controller-797b884cbc-f5qdt inside the ingress-nginx namespace. Running the log shows me that the Ingress is receiving the request I am sending via https://my.domain.com/dl/test.txt

... Ok, I found the error - it was a typo in my nginx-ingress.yaml ... But it is good to have gone through the debug steps once, makes everything a lot less scary :)

Adding TLS to your Ingress

You can generate a self-signed certificate and private key with:

openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout ${KEY_FILE} -out ${CERT_FILE} -subj "/CN=${HOST}/O=${HOST}"`

Then create the secret in the cluster via:

kubectl create secret tls ${CERT_NAME} --key ${KEY_FILE} --cert ${CERT_FILE}

In my case I already use a domain name on my server, so I can head over and create my certificates with Certbot. Certbot will store the certificate inside a folder (named after your domain) inside /etc/letsencrypt - you will get both a fullchain.pem and privkey.pem file that you can use in the Kubernetes command above to add a Secret to your cluster:

kubectl create secret tls my-tls-secret --key /etc/letsencrypt/live/my.domain.com/privkey.pem --cert /etc/letsencrypt/live/my.domain.com/fullchain.pem

Now that we made our cluster aware of the existence of the TLS certificate, we can add it to our NGINX Ingress configuration file:

nginx-ingress.yaml

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: nginx-ingress
  annotations:
    kubernetes.io/ingress.class: "nginx"
    nginx.ingress.kubernetes.io/enable-cors: "true"
    nginx.ingress.kubernetes.io/cors-allow-methods: "GET, POST, PUT"
    nginx.ingress.kubernetes.io/http2-push-preload: "true"
spec:
  tls:
  - hosts:
    - my.domain.com
    secretName: my-tls-secret
  rules:
  - http:
      paths:
        - path: /web
          backend:
            serviceName: web-service
            servicePort: 5678
        - path: /mobile
          backend:
            serviceName: mobile-service
            servicePort: 5678
        - path: /test
          backend:
            serviceName: test-service
            servicePort: 3000
        - path: /dl
          backend:
            serviceName: file-storage
            servicePort: 80

For more Annotations check the official Documentation

You can now access the file server over your domain name: https://my.domain.com/dl/test.txt:

Volume Access Control

Storage configured with a group ID (GID) allows writing only by Pods using the same GID. Mismatched or missing GIDs cause permission denied errors. To reduce the need for coordination with users, an administrator can annotate a PersistentVolume with a GID. Then the GID is automatically added to any Pod that uses the PersistentVolume.

Use the pv.beta.kubernetes.io/gid annotation as follows:

file-storage-pv.yaml

kind: PersistentVolume
apiVersion: v1
metadata:
  name: file-storage-volume
  annotations:
    pv.beta.kubernetes.io/gid: "1234"
  labels:
    type: local
spec:
  storageClassName: manual
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/opt/filecontainer"

file-storage-pod.yaml

kind: Pod
apiVersion: v1
metadata:
  name: file-storage-pod
  annotations:
    pv.beta.kubernetes.io/gid: "1234"
spec:
  volumes:
    - name: file-storage-volume
      persistentVolumeClaim:
       claimName: file-storage-claim
  containers:
    - name: file-storage-container
      image: nginx
      ports:
        - containerPort: 80
          name: "http-file-server"
      volumeMounts:
        - mountPath: "/usr/share/nginx/html"
          name: file-storage-volume

Name		Name	Last commit message	Last commit date
Latest commit History 4 Commits
downloads/dl		downloads/dl
Dockerfile		Dockerfile
README.md		README.md
http-fileserver.yaml		http-fileserver.yaml
image_01.png		image_01.png
image_02.png		image_02.png
image_03.png		image_03.png
image_04.png		image_04.png
image_05.png		image_05.png
image_06.png		image_06.png
image_07.png		image_07.png
image_08.png		image_08.png
image_09.png		image_09.png
image_10.png		image_10.png
image_11.png		image_11.png
image_12.png		image_12.png
image_13.png		image_13.png

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Kubernetes HTTP Fileserver

Serving static files from inside a Docker Container

Serving static files from a PersistentVolume (Recommended)

Create a PersistentVolume

Create a PersistentVolumeClaim

Create a Pod

Creating the Service

Troubleshooting a Service

Adding it to our NGINX Ingress

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Adding TLS to your Ingress

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Kubernetes HTTP Fileserver

Serving static files from inside a Docker Container

Serving static files from a PersistentVolume (Recommended)

Create a PersistentVolume

Create a PersistentVolumeClaim

Create a Pod

Creating the Service

Troubleshooting a Service

Adding it to our NGINX Ingress

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Troubleshooting the NGINX Ingress

Adding TLS to your Ingress

Volume Access Control

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