This is a simple example project of how you can use Nginx as a load balancer in front of your application. This example also includes a deployment descriptor for Pivotal Cloud Foundry and some configuration options that illustrate how PCF does the load balancing between multiple application instances for you out of the box.
docker-compose up
Go to localhost:8080 on your browser and watch the logs. You will notice that your request is forwarded to a different app in a round robin fashion.
Try stopping everything then uncomment the ip_hash in the load-balancer nginx.conf file. This load balancer strategy will cause request to be sent to the same app based on the client ip. Start everything back up and examine the logs as you refresh the browser. You will notice that this time around each of your requests is forwarded to the same app instance.
This project also includes a manifest.yml you can use to deploy the app to PCF. Simply login via the CLI and run the push command.
PCF exposes a route for your app and automatically load balances request to your app in a round robin fashion. Refresh your browser
on the exposed route and watch the response sycle through the app instances.
cf push pcf-node-app
If you want to see the PCF session affinity in action go to your app > settings > user provided environment variables > reveal
and set the USE_SESSION variable to true. Then restage or restart your app. When you navigate to the app via the exposed route
you will notice that you start hitting the same app instance with each refresh of the browser and the app will count the number
of times you have visited. You can examine the request in the browser network and notice the set-cookie header has a copule of values
including JESSIONID and VACAP_ID which PCF uses to route you to the same app instance.
This sticky session feature is useful when you want the user to hit the same app every time. Note that since we are using a client
side cookie to store the session information, the sticky sessionw will persist until it expires in 24hrs or you delete that cookie
via your browser settings.
Notice that the manifest.yml defines two PCF apps with the same configuration and the public route. This demonstrates that the PCF routing layer groups both application instances into a single upstream and load balances the request across all 6 instances.
Note: You will need to set the route in the manifest.yml for PCF to load balance across both apps!
route: pcf-node-app.{your pcf domain here}
Once you enable session affinity it might take a coule of refreshes but you will then be routed to the same instance even though they are split across 2 PCF apps.
- https://docs.cloudfoundry.org/buildpacks/node/index.html
- https://docs.cloudfoundry.org/devguide/deploy-apps/environment-variable.html
- https://docs.cloudfoundry.org/concepts/http-routing.html#sessions
- https://github.com/expressjs/cookie-session
- https://docs.nginx.com/nginx/admin-guide/load-balancer/http-load-balancer/
Happy Coding :D ~!