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Load balancing example

This is a basic example of service registering and load balancing in docker compose, the idea here is: we will have 2 services, frontend and backend, the frontend service will serve html files and potentialy consume the backend service, the backend service will serve a simple python api.

Requirements

Both services will run different subdomains and the need to be scaled freely as needed, this we should,

$ http get api.app.dev
HTTP/1.0 200 OK
Content-Type: application/json
[... omited headers ...]
{ "hostname": "9fdbbe9e4ff8", "message": "Hi there fella" }

and

$ http get app.app.dev
HTTP/1.1 200 OK
Content-Type: text/html
[... omited headers ...]
<!DOCTYPE html>
<html lang="en">
<head> <meta charset="UTF-8"> <title>My stuffs</title> </head>
<body> Hello </body>
</html>

and each of them will need to ve served by different images.

Implementation

For implementation we used apistar for the backend and a simple nginx site for the frontend using their default docker image, finally for load balancing we used the nice dockercloud-haproxy image. Finally as listed in the requirements we're using the git version of apistar just because it implements CORS by default and that makes a lot of sense for APIS.

Run

In this particular case we're using docker-compose however there are other options. To run it you can,

$ docker-compose up
$ # or if you made changes
$ docker-compose up --build

Then you can query any of the services through,

$ curl --header 'Host: app.app.dev' 'http://localhost/'
$ curl --header 'Host: app.app.dev' 'http://localhost/'

That tests the service dicovery part, to test the load balancing try,

$ # after killing the other docker compose up
$ docker-compose up --build --scale api=5
$ # In a different terminal
$ for i in `seq 20`; curl 'http://api.app.dev/'

If you check the logs you'll see that different instances of the api service served those 20 requests.