Kubernetes Using Cloud Shell: Deploy a Python Flask Application

Before You Begin

To successfully perform this tutorial, you must have the following:

1. Prepare

Prepare your environment to create and deploy your application.

Log in to the Oracle Cloud Infrastructure Console.
Open the navigation menu, and click Governance and Administration. Under Governance, click Limits, Quotas and Usage.
Find your service limit for Regions:
- Filter for the following options:
  - Service: Regions
  - Scope: Tenancy
  - Resource: Subscribed region count
  - Compartment: <tenancy-name> (root)
- Find service limit:
  - Limit Name: subscribed-region-count
  - Service Limit: minimum 2
Find your available Compute core count for the VM.Standard.E3.Flex shape:
- Filter for the following options:
  - Service: Compute
  - Scope: <first-availability-domain>. Example: EMlr:US-ASHBURN-AD-1
  - Resource: Cores for Standard.E3.Flex and BM.Standard.E3.128 Instances
  - Compartment: <tenancy-name> (root)
- Find available core count:
  - Limit Name: standard-e3-core-ad-count
  - Available: minimum 1
- Repeat for Scope: <second-availability-domain> and <third-availability-domain>. Each region must have at least one core available for this shape.
Find out if you have 50 GB of Block Volume available:
- Filter for the following options:
  - Service: Block Volume
  - Scope: <first-availability-domain>. Example: EMlr:US-ASHBURN-AD-1
  - Resource Volume Size (GB)
  - Compartment: <tenancy-name> (root)
- Find available core count:
  - Limit Name: total-storage-gb
  - Available: minimum 50
- Repeat for Scope: <second-availability-domain> and <third-availability-domain>. Each region must have at least 50 GB of block volume available.
Find out how many Flexible Load Balancers you have available:
- Filter for the following options:
  - Service: LbaaS
  - Scope: <your-region>. Example: us-ashburn-1
  - Resource: <blank>
  - Compartment: <tenancy-name> (root)
- Find the count for the following shapes
  - Limit Name: lb-flexible-bandwidth-count
  - Available: minimum 1

Note

This tutorial creates three compute instances with a VM.Standard.E2.1 shape for the cluster nodes. To use another shape, filter for its core count. For example, for VM.Standard2.4, filter for Cores for Standard2 based VM and BM Instances and get the count.

For a list of all shapes, see VM Standard Shapes.

Note

This tutorial creates three compute instances with a VM.Standard.E3.Flex shape for the cluster nodes. To use another shape, filter for its core count. For example, for VM.Standard2.4, filter for Cores for Standard2 based VM and BM Instances and get the count.

For a list of all shapes, see VM Standard Shapes.

Note

This tutorial uses a 'Quick Create' workflow to create a cluster with a public regional subnet that hosts a flexible load balancer. To use a different load balancer, you can use a custom workflow to explicitly specify which existing network resources to use, including the existing subnets in which to create the load balancers.

To use another bandwidth for the load balancer, filter for its count, for example 100-Mbps bandwidth or 400-Mbps bandwidth.

Create an Authorization Token

Gather Required Information

2. Set Up a Cluster

Install and configure management options for your Kubernetes cluster. Later, deploy your application to this cluster.

Add Compartment Policy

If your username is in the Administrators group, then skip this section. Otherwise, have your administrator add the following policy to your tenancy:

allow group <the-group-your-username-belongs> to manage compartments in tenancy

With this privilege, you can create a compartment for all the resources in your tutorial.

Steps to Add the Policy

In the navigation bar, select the Profile menu and then select User settings or My profile, depending on the option that you see.
In the left pane, click Groups.
In a notepad, copy the Group Name that your username belongs.
Open the navigation menu and click Identity & Security. Under Identity, click Policies.
Click Create Policy.
Fill in the following information:
- Name: manage-compartments
- Description: Allow the group <the-group-your-username-belongs> to list, create, update, delete and recover compartments in the tenancy.
- Compartment: <your-tenancy>(root)
For Policy Builder, click Show manual editor.

Paste in the following policy:

allow group <the-group-your-username-belongs> to manage compartments in tenancy

Click Create.

Reference

The compartments resource-type in Verbs + Resource-Type Combinations for IAM

Create a Compartment

Add Resource Policy

If your username is in the Administrators group, then skip this section. Otherwise, have your administrator add the following policy to your tenancy:

allow group <the-group-your-username-belongs> to manage all-resources in compartment <your-compartment-name>

With this privilege, you can manage all the resources in your compartment, essentially giving you administrative rights in that compartment.

Steps to Add the Policy

Create a Cluster with 'Quick Create'

Configure Cloud Shell to Access to Your Cluster

After you create a Kubernetes cluster, set up Cloud Shell to access the cluster.

Sign in to the Oracle Cloud Infrastructure Console.
Open the navigation menu and click Developer Services. Under Containers & Artifacts, click Kubernetes Clusters (OKE).
Click the link to <your-cluster>.

The information about your cluster is displayed.
Click Access Cluster.
Click Cloud Shell Access. Follow the steps in the dialog. The following steps are provided for your reference.
Click Launch Cloud Shell. Alternatively, from the main menu, you can click the Cloud Shell icon () and start a session.
Check your oci CLI version and verify that Cloud Shell is working.
```
oci -v
```
Create kubeconfig file for your setup. Use the information from Access Your Cluster dialog.
```
oci ce cluster create-kubeconfig <use data from dialog>
```
You get a message that:
```
New config written to the Kubeconfig file <your-home-directory>/.kube/config
```
Note

If the config file is not stored in its default location (~/.kube/config, you must export the KUBECONFIG environment variable to point to the location.
```
export KUBECONFIG=$HOME/<new-location>/config
```
Note

When working with more than one cluster, you specify a specific config file on the command line. Example:
```
kubectl --kubeconfig=</path/to/config/file> <some-command>
```
Test your cluster configuration with the following command.
List clusters:
```
kubectl get service
```

With your cluster access setup, you are now ready to prepare your application for deployment.

3. Build your Docker Application

Next, set up the Flask framework on Cloud Shell. Then, create and run a Python application.

Create a Local Application

Create your Flask application.

Install Flask.
```
pip3 install --user Flask
```
Create a directory for your application.
```
mkdir python-hello-app
```
Change to the python-hello-app directory.
```
cd python-hello-app
```

Create a "Hello, World!" application.

Create the file:

vi hello.py

In the file, input the following text:

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
    return '<h1>Hello World from Flask!</h1>'

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=int("5000"), debug=True)

Save the file.

Run the Local Application

Run your Flask application.

Run the Python program.

export FLASK_APP=hello.py
export FLASK_ENV=development
python3 hello.py

Produces the following output:

* Serving Flask app 'hello' (lazy loading)
* Environment: development
* Debug mode: on
* Running on all addresses.
WARNING: This is a development server. Do not use it in a production deployment.
* Running on http://x.x.x.x:5000/ (Press CTRL+C to quit)
* Restarting with stat
* Debugger is active!
* Debugger PIN: xxx-xxx-xxx

Move the app to the background.
- Hit Ctrl z.
- Enter the following command: bg
Test the app using curl.
In Cloud Shell terminal, enter the following code:
```
curl -X GET http://localhost:5000
```
Output:
```
<h1>Hello World from Flask!</h1>
```
Stop the running application.
- When you are done testing, get the process ID for your application.
```
ps -ef
```
- Stop the process.
```
kill <your-pid>
```

You have successfully created a local Python application with the Flask framework.

References:

For more information on Flask, see Flask Documentation.

Build a Docker Image

Next, create a Docker image for your Flask application.

First, ensure you are in the python-hello-app directory.

Create a file named Dockerfile:

Create the file:

vi Dockerfile

In the file, input the following text and save the file:

FROM python:3.9-slim-buster
ADD hello.py /
COPY . /app
WORKDIR /app
RUN pip3 install Flask
EXPOSE 5000
CMD [ "python3", "./hello.py" ]

Build a Docker image:

docker build -t python-hello-app .

You get a success message.

[INFO] BUILD SUCCESS
Successfully tagged python-hello-app:latest

Run the Docker image:

docker run --rm -p 5000:5000 python-hello-app:latest &

Test the application using the curl command:
```
curl -X GET http://localhost:5000
```
If you get <h1>Hello World from Flask!</h1>, then the Docker image is running. Now you can push the image to Container Registry.
Stop the running application.
- When you are done testing, get the process ID for your application.
```
ps -ef
```
- Stop the process.
```
kill <your-pid>
```

Congratulations! You have successfully created a Python Flask Docker image.

4. Deploy Your Docker Image

With your Python image created, now you can deploy it.

Create a Docker Repository

Open the navigation menu and click Developer Services. Under Containers & Artifacts, click Container Registry.
In the left navigation, select <your-compartment-name>.
Click Create Repository.
Create a private repository with your choice of repo name:
```
<repo-name> = <image-path-name>/<image-name>
```
Example: flask-apps/python-hello-app
You are now ready to push your local image to Container Registry.
Note

Before you can push a Docker image into a registry repository, the repository must exist in your compartment. If the repository does not exist, the Docker push command does not work correctly.
Note

The slash in a repository name does not represent a hierarchical directory structure. The optional <image-path-name> helps to organize your repositories.

Push Your Local Image

With your local Docker image created, push the image to the Container Registry.

Follow these steps.

Open a terminal window.
Log in to Container Registry:
```
docker login <region-key>.ocir.io
```
You are prompted for your login name and password.
- Username: <tenancy-namespace>/<user-name>
- Password: <auth-token>
List your local Docker images:
```
docker images
```
The Docker images on your system are displayed. Identify the image you created in the last section: python-hello-app
Tag your local image with the URL for the registry plus the repo name, so you can push it to that repo.
```
docker tag <your-local-image> <repo-url>/<repo-name>
```
- Replace <repo-url> with:
```
<region-key>.ocir.io/<tenancy-namespace>/
```
- Replace <repo-name> with:
  <image-folder-name>/<image-name> from the Create a Docker Repository section.
- Here is an example after combining both:
```
docker tag python-hello-app iad.ocir.io/my-namespace/flask-apps/python-hello-app
```
  In this example, the components are:
  - Repo URL: iad.ocir.io/my-namespace/
  - Repo name: flask-apps/python-hello-app
Note

OCI Container Registry now supports creating a registry repo in any compartment rather than only in the root compartment (tenancy). To push the image to the repo you created, combine the registry URL with the exact repo name. OCI Container Registry matches the unique repo name and pushes your image.
Check your Docker images to see if the image is copied.
```
docker images
```
- The tagged or the copied image has the same image ID as your local image.
- The copied image name is:
```
<region-key>.ocir.io/<tenancy-namespace>/<image-folder-name>/<image-name>
```

Push the image to Container Registry.

docker push <copied-image-name>:latest

Example:

docker push iad.ocir.io/my-namespace/flask-apps/python-hello-app:latest

Open the navigation menu and click Developer Services. Under Containers & Artifacts, click Container Registry.

Find your image in Container Registry after the push command is complete.

Deploy the Image

With your image in Container Registry, you can now deploy your image and app.

Create a registry secret for your application. This secret authenticates your image when you deploy it to your cluster.
To create your secret, fill in the information in this template .
```
kubectl create secret docker-registry ocirsecret --docker-server=<region-key>.ocir.io  --docker-username='<tenancy-namespace>/<user-name>' --docker-password='<auth-token>'  --docker-email='<email-address>'
```
After the command runs, you get a message similar to: secret/ocirsecret created.
Verify that the secret is created. Issue the following command:
```
kubectl get secret ocirsecret --output=yaml
```
The output includes information about your secret in the yaml format.

Determine the host URL to your registry image using the following template:

<region-code>.ocir.io/<tenancy-namespace>/<repo-name>/<image-name>:<tag>

Example:

iad.ocir.io/my-namespace/flask-apps/python-hello-app:latest

On your system, create a file called app.yaml with the following text:

Replace the following place holders:

<your-image-url>
<your-secret-name>

apiVersion: apps/v1
kind: Deployment
metadata:
  name: app
spec:
  selector:
    matchLabels:
      app: app
  replicas: 3
  template:
    metadata:
      labels:
        app: app
    spec:
      containers:
      - name: app
        image: <your-image-url>
        imagePullPolicy: Always
        ports:
        - name: app
          containerPort: 5000
          protocol: TCP
      imagePullSecrets:
        - name: <your-secret-name>
---
apiVersion: v1
kind: Service
metadata:
  name: app-lb
  labels:
    app: app
  annotations:
    service.beta.kubernetes.io/oci-load-balancer-shape: "flexible"
    service.beta.kubernetes.io/oci-load-balancer-shape-flex-min: "10"
    service.beta.kubernetes.io/oci-load-balancer-shape-flex-max: "100"
spec:
  type: LoadBalancer
  ports:
  - port: 5000
  selector:
    app: app

Deploy your application with the following command.
```
kubectl create -f app.yaml
```
Output:
```
deployment.apps/app created
```
Note

In the app.yaml file, the code after the dashes adds a flexible load balancer.

Test Your App

After you deploy your app, it might take the load balancer a few seconds to load.

Check if the load balancer is live:
```
kubectl get service
```
Repeat the command until load balancer is assigned an IP address.
Note

While waiting for the load balancer to deploy, you can check the status of your cluster with these commands:
- Get each pods status: kubectl get pods
- Get app status: kubectl get deployment
Use the load balancer IP address to connect to your app in a browser:
```
http://<load-balancer-IP-address>:5000
```
The browser displays: <h1>Hello World from Flask!</h1>
Undeploy your application from the cluster. (Optional) To remove your application run this command:
```
kubectl delete -f app.yaml
```
Output:
```
deployment.apps/python-hello-app deleted
service "python-hello-app-lb" deleted
```
Your application is now removed from your cluster.

What's Next

You have successfully created a Hello World Python application, deployed it to a Kubernetes cluster and made it accessible on the internet, using the Flask framework.

Check out these sites to explore more information about development with Oracle products:

Oracle Cloud Infrastructure Documentation

Kubernetes Using Cloud Shell: Deploy a Python Flask Application

Before You Begin 🔗

1. Prepare 🔗

2. Set Up a Cluster 🔗

3. Build your Docker Application 🔗