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testFlask

Python Flask Application for Openshift 4 Example/Demo

testFlask

Test Flask is a simple flask application to show some parts of the OpenShift Application Experience for a Python Application. It’s been broken down into a series of modules that cover likely Use Cases.

Modules

Module 1: testFlask - Main Application(This Page)

Module 2: Custom s2i Images - Create Custom s2i Images for Python Applications

Module 3: testFlask-Jenkins - Create Same Application with a Jenkins Pipeline in OpenShift

Module 4: testFlask-Tekton - Create Same Application with a Tekton Pipeline in OpenShift

Module 5: testFlask-Oauth - Application authentication using OpenShift Oauth Proxy

Module 6: testflask-gitops - ArgoCD Application Continous Deployment

Module 7: testflask-helm-repo - Deploy the Same Application via Helm

Module 8: python-openshift-remote-debugging-vscode-example - Remote Debugging Application

Steps to Build and Run Application

Source Environment Variables

eval "$(curl https://raw.githubusercontent.com/MoOyeg/testFlask/master/sample_env)"

Create necessary projects

oc new-project $NAMESPACE_DEV

oc new-project $NAMESPACE_PROD

This step is ONLY necessary if you are using a private repo
Create Secret in OpenShift for Private/Cluster, example is for github ssh key
```
oc create secret generic $REPO_SECRET_NAME --type=kubernetes.io/ssh-auth --from-file=ssh-privatekey=$SSHKEY_PATH -n $NAMESPACE_DEV
```
Link Secret with your Service Account,the default Service account for builds is usually builder so will link with builder
```
oc secrets link builder $REPO_SECRET_NAME -n $NAMESPACE_DEV
```

Create a new Secret for our database(mysql) credentials

oc create secret generic my-secret --from-literal=MYSQL_USER=$MYSQL_USER --from-literal=MYSQL_PASSWORD=$MYSQL_PASSWORD -n $NAMESPACE_DEV

Create a new mysql instance(Application will use sqlite if no mysql detail is provided).Please see Openshift Builds and Openshift S2i to understand more.
```
oc new-app $MYSQL_HOST --env=MYSQL_DATABASE=$MYSQL_DATABASE -l db=mysql -l app=testflask -n $NAMESPACE_DEV
```
The mysql app above will fail because we have not provided the MYSQL user and password,we can provide our previously created database secret to the mysql deployment.
```
oc set env deploy/$MYSQL_HOST --from=secret/my-secret -n $NAMESPACE_DEV
```

Create our application on openshift. We have options to build our application image using s2i or Dockerfile. There are other methods not discussed here.

Example of creating application from a Private Repo with Source Secret(s2i Building)

oc new-app python:3.8~git@github.com:MoOyeg/testFlask.git --name=$APP_NAME --source-secret$REPO_SECRET_NAME -l app=testflask --strategy=source  --env=APP_CONFIG=./gunicorn/gunicorn.conf.py --env=APP_MODULE=runapp:app --env=MYSQL_HOST=$MYSQL_HOST --env=MYSQL_DATABASE=$MYSQL_DATABASE -n $NAMESPACE_DEV

Example of creating application from Public Repo without Source Secret(s2i Building)

oc new-app python:3.8~https://github.com/MoOyeg/testFlask.git --name=$APP_NAME -l app=testflask --strategy=source --env=APP_CONFIG=./gunicorn/gunicorn.conf.py --env=APP_MODULE=runapp:app --env=MYSQL_HOST=$MYSQL_HOST --env=MYSQL_DATABASE=$MYSQL_DATABASE -n $NAMESPACE_DEV

Example of creating application from Public Repo using the Dockerfile to build(Docker Strategy)

oc tag --source=docker registry.redhat.io/ubi8/ubi:latest ubi8:latest -n openshift

oc new-app https://github.com/MoOyeg/testFlask.git --name=$APP_NAME -l app=testflask --env=MYSQL_HOST=$MYSQL_HOST --env=MYSQL_DATABASE=$MYSQL_DATABASE -n $NAMESPACE_DEV --strategy=docker

Externalizing Application configuration from application code is good practise. We will patch environment Details with Configuration information from Configmap and DownWardAPI.We externalize configration in configmap to allow changes without updating code. We are using the DownWardAPI patch to provide platform details to our application.
- Store Gunicorn Configuration in configmap
```
oc create configmap testflask-gunicorn-config --from-file=./gunicorn/gunicorn.conf.py -n $NAMESPACE_DEV
```
- Provide Gunicorn Configuration to our Application as a volume and overwrite exisitng file.
```
oc set volume deploy/testflask --add --configmap-name testflask-gunicorn-config --mount-path /app/gunicorn --type configmap -n $NAMESPACE_DEV
```
- Provide Platform Information to Application via a patch and request to Kubernetes API.
```
oc patch deploy/$APP_NAME --patch "$(curl https://raw.githubusercontent.com/MoOyeg/testFlask/master/patch-env.json | envsubst)" -n $NAMESPACE_DEV
```
Expose the service to the outside world with an OpenShift route
```
oc expose svc/$APP_NAME --port 8080 -n $NAMESPACE_DEV
```
We can provide our previously created database secret to your app deployment, so ythe app can move to using our provisioned mysql rather than in-mem sqlite.
```
oc set env deploy/$APP_NAME --from=secret/my-secret -n $NAMESPACE_DEV
```
You should be able to log into the OpenShift console now to get a better look at the application, all the commands above can be run in the console, to get more info about the developer console please visit Openshift Developer Console.

To make the seperate deployments appear as one app in the Developer Console, you can label them. This step does not change app behaviour or performance is a visual aid and would not be required if app was created from developer console.

oc label deploy/$APP_NAME app.kubernetes.io/part-of=$APP_NAME -n $NAMESPACE_DEV

oc label deploy/$MYSQL_HOST app.kubernetes.io/part-of=$APP_NAME -n $NAMESPACE_DEV

oc annotate deploy/$APP_NAME app.openshift.io/connects-to=$MYSQL_HOST -n $NAMESPACE_DEV

Webhooks

You can attach a WebHook to your application , so when there is an application code change the application is automatically rebuilt in openshift.You can see steps to this via the developer console .OpenShift will create the html link and secret for you which you can configure in github/gitlab other generic VCS. See more here Openshift Triggers and see github webhooks.
- To get the Webhook Link from the CLI
```
oc describe bc/$APP_NAME -n $NAMESPACE_DEV | grep -i -A1 "webhook generic"
```
- To get the Webhook Secret from the CLI
```
oc get bc/$APP_NAME -n $NAMESPACE_DEV -o jsonpath='{.spec.triggers[*].github.secret}'
```
- Content Type is application/json and disable ssl verification if your cluster does not have a trusted cert.

Health Checks

It is important to be able to provide the status of your application to the Kubernetes platform. It allows the platform take corrective action to application instances that are not ready or available to recieve traffic .This can be done with a liveliness, health and startup probes. please see Health Checks. This application has sample /health and /ready uri that provide responses about the status of the application.
- Create a readiness probe for our application
```
oc set probe deploy/$APP_NAME --readiness --get-url=http://:8080/ready --initial-delay-seconds=10 -n $NAMESPACE_DEV
```
- Create a liveliness probe for our application
```
oc set probe deploy/$APP_NAME --liveness --get-url=http://:8080/health --timeout-seconds=30 --failure-threshold=3 --period-seconds=10 -n $NAMESPACE_DEV
```
- We can test OpenShift Readiness by opening the application page and setting the application ready to down, after a while the application endpoint will be removed from the list of endpoints that recieve traffic for the service,you can confirm by.
  - Application will no longer have endpoints, meaning no traffic will be recieved.
    oc get ep/$APP_NAME -n $NAMESPACE_DEV
  - Since the readiness removes the pod endpoint from the service we will not be able to access the app page anymore.We will need to log into the pod to enable the readiness back.
    POD_NAME=$(oc get pods -l deployment=$APP_NAME -n $NAMESPACE_DEV -o name | head -n 1)
  - Exec the Pod and curl the pod API to start the pod readiness
    oc exec $POD_NAME curl http://localhost:8080/ready_down?status=up
- We can test OpenShift Liveliness also, when a pod fails it’s liveliness check, it is restarted based on the parameters used in the liveliness check, see liveliness probe command above.
  - Set the Pod’s liveliness to down
    POD_NAME=$(oc get pods -l deploymentconfig=$APP_NAME -n $NAMESPACE_DEV -o name | head -n 1)``` ```oc exec $POD_NAME curl http://localhost:8080/health_down?status=down

Horizontal AutoScaling with CPU/Memory

Let’s horizonatally autoscale based on Pod CPU Metrics.

Set Limits and Requests for HPA Object to use

  oc set resources deploy/$APP_NAME --requests=cpu=10m,memory=80Mi --limits=cpu=20m,memory=120Mi -n $NAMESPACE_DEV

Confirm PodMetrics are available for pod before continuing

   POD_NAME=$(oc get pods -l deploymentconfig=$APP_NAME -n $NAMESPACE_DEV -o name | head -n 1)

   oc describe PodMetrics $POD_NAME -n $NAMESPACE_DEV

Create Horizontal Pod Autoscaler with 50% Average CPU

  oc autoscale deploy/$APP_NAME --max=3 --cpu-percent=50 -n $NAMESPACE_DEV

Send Traffic to Pod to Increase CPU usage and force scaling.

  ROUTE_URL=$(oc get route $APP_NAME -n $NAMESPACE_DEV -o jsonpath='{ .spec.host }')

  export counter=0 && while :;do curl -X POST "$ROUTE_URL/insert?key=$counter&value=$counter" && eval counter=$(($counter+1));done

Vertical Pod Autoscaler

Let’s vertically autoscale based on Pod CPU Metrics.

Make sure the VPA Operator is installed. Please see VPA Operator

Might be necessary to give Service Account Permission on Namespace

oc adm policy add-cluster-role-to-user edit system:serviceaccount:openshift-vertical-pod-autoscaler:vpa-recommender -n $NAMESPACE_DEV

Create VPA CR for deployment

    echo """
      apiVersion: autoscaling.k8s.io/v1
      kind: VerticalPodAutoscaler
      metadata:
        name: vpa-recommender
      spec:
        targetRef:
          apiVersion: "apps.openshift.io/v1"
          kind:       Deployment
          name:       $APP_NAME
        updatePolicy:
          updateMode: "Auto" """ | oc create -f - -n $NAMESPACE_DEV

VPA will automatically try to apply changes if it differs significantly from configured resource but we can see VPA recommendation for DeploymentConfig.
```
oc get vpa vpa-recommender -n $NAMESPACE_DEV -o json | jq '.status.recommendation'
```

Monitoring and AutoScaling Application Metrics

Openshift also provides a way for you to use Openshift’s platform monitoring to monitor your application metrics and provide alerts on those metrics.Note, this functionality is still in Tech Preview.This only works for applications that expose a /metrics endpoint that can be scraped which this application does. Please visit Monitoring Your Applications and you can see an example of how to do that here, before running any of the below steps please enable monitoring using info from the links above.

Create a servicemonitor using below code (Please enable cluster monitoring with info from above first), servicemonitor label must match label specified from the deployment above.

cat << EOF | oc create -f -
apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  labels:
    k8s-app: prometheus-testflask-monitor
  name: prometheus-testflask-monitor
  namespace: $NAMESPACE_DEV
spec:
  endpoints:
  - interval: 30s
    targetPort: 8080
    scheme: http
  selector:
    matchLabels:
      app: $APP_NAME
EOF

After the servicemonitor is created we can confirm by looking up the application metrics under monitoring–>metrics, one of the metrics exposed is Available_Keys(Type Available_Keys in query and run) so as more keys are added on the application webpage we should see this metric increase.

We can also create alerts based on Application Metrics using the Openshift’s Platform AlertManager via Prometheus,Openshift Alerting.We need to create an Alerting Rule to recieve Alerts.

cat << EOF | oc create -f -
apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
  name: testflask-alert
  namespace: $NAMESPACE_DEV
spec:
  groups:
  - name: $APP_NAME
    rules:
    - alert: DB_Alert
      expr: Available_Keys{job="testflask"} > 4
EOF

The above alert should only fire when we have more than 4 keys in the application, go to the application webpage and add more than 4 keys to the DB, we should get an alert when we go to Monitoring-Alerts-AlertManager UI(Top of Page).

OpenShift Serverless

Openshift provides serverless functionality via the Openshift serverless operator, Follow steps in documenation to create serveless installation**

Create a sample serverless application below and run application.

cat << EOF | oc create -f -
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: testflask-serverless
  namespace: $NAMESPACE_DEV
spec:
  template:
    spec:
      containers:
        - image: image-registry.openshift-image-registry.svc:5000/${NAMESPACE_DEV}/${APP_NAME}:latest      
          env:
          - name: APP_CONFIG
            value: "gunicorn.conf.py"
          - name: APP_MODULE
            value: "runapp:app"
          - name: MYSQL_HOST
            value: $MYSQL_HOST
          - name: MYSQL_DATABASE 
            value: $MYSQL_DATABASE
EOF

ASGI/Quart/Uvicorn

Build and Alternate version of the testflask application using ASGI and Uvicorn**

Build custom builder image of uvicorn(Sample provided)

   oc new-build https://github.com/MoOyeg/s2i-python-custom.git --name=s2i-ubi8-uvicorn --context-dir=s2i-ubi8-uvicorn -n $NAMESPACE_DEV

Build Application Image using previous image with custom gunicorn worker

   oc new-app s2i-ubi8-uvicorn~https://github.com/MoOyeg/testFlask.git#quart --name=testquart -l app=testquart --strategy=source --env=APP_CONFIG=gunicorn-uvi.conf --env=APP_MODULE=testapp:app --env CUSTOM_WORKER="true" -n $NAMESPACE_DEV