ks4.md

Kubernetes series part 4

The objective here is to update our app so that we can detect server code changes on the fly. This will speed up our backend development cycles while still working with kubernetes in a development environment.

The flask development server has a nice reload experience:

The flask command line script (Command Line Interface) is strongly recommended for development because it provides a superior reload experience due to how it loads the application. The basic usage is like this:

export FLASK_APP=my_application
export FLASK_DEBUG=1
flask run

From: Source: Development Server

We will use this behaviour to get reload exeprience with the app we are building.

1. navigate to ks4

   ➜ pwd
       ~/dev/github/redgate/ks/ks4

2. start minikube

   ➜ minikube start

3. switch to minikube context

   ➜ eval $(minikube docker-env)

   If you ever need to switch back to your machine's context do:

   ➜ eval $(docker-machine env -u)

4. build web docker image

   ➜ docker build -f ./web/Dockerfile -t ks4webimage .

5. build web server docker image

   ➜ docker build -f ./server/Dockerfile -t ks4webserverimage .

6. mount ks4 source code

   In a separate terminal, in the root of the project (this terminal needs to keep running the whole time you're debugging...).

   ➜ pwd
       ~/dev/github/redgate/ks/ks4
   ➜ minikube mount .:/mounted-ks4-src
       Mounting . into /mounted-ks4-app-src on the minikube VM
       This daemon process needs to stay alive for the mount to still be accessible...
       ufs starting

   For more information about mounting volumes read these docs

7. add environment variable to webserver section in deployment yaml file

   As described in the flask docs we will add the FLASK_DEBUG environment variable to get the reloading experience we want.

   command: ["python"]
   args: ["-m", "flask", "run"]
   env:
   - name: FLASK_DEBUG
       value: "1"
   ports:
   - containerPort: 5000

8. add the web server volumes to the deployment yaml file

   Update the global volume section of the ./config/dev.ks.deployment.yaml with a python-server volume that points to the python backend so that changes are picked up on save.

   volumes:
   - name: python-server
   hostPath:
       path: /mounted-ks4-src/server
   - name: frontend
   hostPath:
       path: /mounted-ks4-src/app/src

   Then reference it in the webserver image section

   volumeMounts:
   - mountPath: /server
   name: python-server

9. create deployment and service

   ➜ kubectl create -f ./config/dev.ks.deployment.yaml
       deployment "ks4web" created
   
   ➜ kubectl create -f ./config/dev.ks.service.yaml
       service "ks4web" created
   ➜ kubectl get all
       NAME            DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
       deploy/ks4web   1         1         1            1           31s
   
       NAME                   DESIRED   CURRENT   READY     AGE
       rs/ks4web-2671084145   1         1         1         31s
   
       NAME            DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
       deploy/ks4web   1         1         1            1           31s
   
       NAME                         READY     STATUS    RESTARTS   AGE
       po/ks4web-2671084145-f0f71   2/2       Running   0          31s

10. get web server logs

    ➜ kubectl logs ks4web-2671084145-f0f71 ks4webserver
        * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
        * Restarting with stat
        /usr/local/lib/python3.5/runpy.py:125: RuntimeWarning: 'flask.cli' found in sys.modules after import of package 'flask', but prior to execution of 'flask.cli'; this may result in unpredictable behaviour
        warn(RuntimeWarning(msg))
        * Debugger is active!
        * Debugger PIN: 207-014-748

11. service ks4web

    ➜ minikube service ks4web --url

12. check backend updates by changing the hello.py controller

    If you attach the logs with -f and update ./server/controllers/hello.py you should see

    Detected change in '/server/controllers/hello.py', reloading` in the logs.

    Full logs:

    ➜ kubectl logs ks4web-2671084145-gtz9q ks4webserver -f
        * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
        * Restarting with stat
        /usr/local/lib/python3.5/runpy.py:125: RuntimeWarning: 'flask.cli' found in sys.modules after import of package 'flask', but prior to execution of 'flask.cli'; this may result in unpredictable behaviour
        warn(RuntimeWarning(msg))
        * Debugger is active!
        * Debugger PIN: 207-014-748
        --------------------------------------------------------------------------------
        INFO in hello [/server/controllers/hello.py:8]:
        hello controller called
        --------------------------------------------------------------------------------
        127.0.0.1 - - [23/Oct/2017 09:53:50] "GET /api/hello HTTP/1.1" 200 -
        * Detected change in '/server/controllers/hello.py', reloading
        * Restarting with stat
        /usr/local/lib/python3.5/runpy.py:125: RuntimeWarning: 'flask.cli' found in sys.modules after import of package 'flask', but prior to execution of 'flask.cli'; this may result in unpredictable behaviour
        warn(RuntimeWarning(msg))
        * Debugger is active!
        * Debugger PIN: 207-014-748
        --------------------------------------------------------------------------------
        INFO in hello [/server/controllers/hello.py:8]:
        hello controller called

    If you then refresh the browser you should see the changes in the UI.

13. minikube mounted volume command should detect this changes

    ➜ minikube mount .:/mounted-ks4-src
        Mounting . into /mounted-ks4-src on the minikube VM
        This daemon process needs to stay alive for the mount to still be accessible...
        ufs starting
        Rename ./server/controllers/__pycache__/hello.cpython-35.pyc.140423133386000 to hello.cpython-35.pyc
        rel  results in server/controllers/__pycache__/hello.cpython-35.pyc
        rename ./server/controllers/__pycache__/hello.cpython-35.pyc.140423133386000 to server/controllers/__pycache__/hello.cpython-35.pyc gets <nil>