How to run it

Create docker network:

$ docker network create nginx-kat

Run the main application first:

$ cd flask_application
$ docker build -t flask-app .
$ docker run --name flask1 -it -p 27015:27015 -d --network nginx-kat main-flask-app

Run the mirror application (continued from the previous steps):

$ docker run --name flask2 -it -p 27016:27015 -d --network nginx-kat main-flask-app

Finally spin up Nginx:

$ cd ..
$ docker build -t custom-nginx .
$ docker run --name nginx-test-kat -d -p 8180:80 --network nginx-kat custom-nginx

Notes

• Make sure to run docker ps to confirm the containers were spinned up properly and running.
• If the container does not run, try docker logs [container name] to investigate.
• -p 8180:80 does port forwarding, which maps the localhost 8180 to docker port 80.
• When running the main application, -p 27015:27015 maps localhost 27015 to docker port 27015
  • Docker port 27015 is defined in /flask_application/Dockerfile.
  • EXPOSE 27015 allows the external traffic (outside docker) to access the 27015 port inside docker.
  • The 27015 in CMD [ "flask", "run","--host","0.0.0.0","--port","27015"] command runs the flask application on 27015 inside docker.
• The flask program simply counts and display the number of requests that hit the server.
• We need to add resolver 127.0.0.11; for /mirror in nginx.conf to make the mirroring to work
  • 127.0.0.11 is the docker internal DNS server address

How to test it

• Go to localhost:8081, and hit the endpoint 10 times
• Go to localhost:27015 (the main server), should see number 11
• Go to localhost:27016 (the mirror server), should see number 11 (depending on the settings of Nginx)