load_balancing

Experiments with load balancing a flask app using nginx or haproxy

Run nginx version:

todo

Run haproxy preconfigured version:

From project root, for 3 web-servers:

docker-compose -f compose-haproxy-preconf.yml up --scale hiworld=3

Connect to port localhost:8080 to see the load balancing effect.

Run haproxy custom version

Useful for playing with haproxy config file parameters.

docker-compose -f compose-haproxy-custom.yml up             # Builds initial containers and creates network

Optional - give it a better name

Because the project directory is called src, you'll get containers named like src_redis_1. If you want a better name, add the argument -p, --project-name to docker-compose:

docker-compose -f compose-haproxy-preconf.yml -p hi-hiproxy up

To scale down

I find (Docker for Mac 17.03.1-ce, compose 1.11.2) simply re-running docker-compose scale with a lower count doesn't reduce the count on the next docker-compose up, you must first run docker-compose down, re-scale, then back up to get the reduction.

Testing the load balancers

Initially, running the bash command below will demonstate round-robin behaviour by the load balancers. The hostname will change as the hit counter increments.

for i in {1..10}; do time curl localhost:8080; done;