Two Load-Balancers Across Two Ports

The Goals

This takes advantage of some notes already written in a previous post on nginx as a load-balancer.
Here, 2 nginx instances will...

listen on 2 ports : 8081 and 8082
"pass" the requests to 3 round-robin node apps
- here, the two instances of nginx will each have 3 (different) node backend instances to "forward" the requests to
The Goals
The Node Server
The NGINX Load-Balancers
- Config 1 - half the node instances on port 8081
- Config 2 - half the node instances
Build a Docker Network
Run And Connect All Of the Containers
- 3x the node app
- The NGINX container
Test The Setup
Compose For A Different Approach

A Diagram

The Node Server

See the previous post for a trivial node api, which includes...

The Server: a trivial node rest api
Containerizing The Server: building a dockerfile, building an image from the dockerfile, and running container

The NGINX Load-Balancers

With the goal here being to have 2x nginx instances running, 2 nginx config files will be built.
The files will be nearly identical:

the servers listed in the "nodebackend" section will be named differently between the 2 nginx instnaces
the port that reverse proxy listens on will be differently between the 2 nginx instnaces

Config 1 - half the node instances on port 8081

Here's the nginx config:

# the context here: http context
http {

  # defaults to a "round-robin" method for load balancing across servers
  # here, the servers are named "nodebackend"
  upstream nodebackend {

    server nodeapp1:8080;
    server nodeapp2:8080;
    server nodeapp3:8080;

  }

  server {
    # here, listening on port 8081
    listen 8081;
    location / {
      
      proxy_pass http://nodebackend/;
    }
  }
}

# can set things like maximum-worker-connections...
events {}

The nginx config is setup to listen on port 8081 and round-robin balance the requests to 3 different apps: nodeapp1 on port 8080, nodeapp2 on port 8080, and nodeapp3 on port 8080.

Config 2 - half the node instances

Here's the nginx config, maybe name it nginx2.conf:

# the context here: http context
http {

  # defaults to a "round-robin" method for load balancing across servers
  # here, the servers are named "nodebackend"
  upstream nodebackend {

    server nodeapp4:8080;
    server nodeapp5:8080;
    server nodeapp6:8080;

  }

  server {
    # here, listening on port 8082
    listen 8082;
    location / {
      
      proxy_pass http://nodebackend/;
    }
  }
}

# can set things like maximum-worker-connections...
events {}

The nginx config is setup to listen on port 8082 and round-robin balance the requests to 3 different apps: nodeapp4 on port 8080, nodeapp5 on port 8080, and nodeapp5 on port 8080.

Build a Docker Network

In order for the containers to be able to "talk to" each other, they all will get put on the same network. Here, this network will be called nxnet: docker network create nxnet.

Run And Connect All Of the Containers

6x the node app

This showcase one nice detail of working with docker: spinning up 6 node apis from the same image:

docker run --hostname nodeapp1 --network nxnet name nodeapp1 --env API_PORT=8080 -d nodebox
docker run --hostname nodeapp2 --network nxnet name nodeapp2 --env API_PORT=8080 -d nodebox
docker run --hostname nodeapp3 --network nxnet name nodeapp3 --env API_PORT=8080 -d nodebox
docker run --hostname nodeapp4 --network nxnet name nodeapp4 --env API_PORT=8080 -d nodebox
docker run --hostname nodeapp5 --network nxnet name nodeapp5 --env API_PORT=8080 -d nodebox
docker run --hostname nodeapp6 --network nxnet name nodeapp6 --env API_PORT=8080 -d nodebox

The above commands include the --network nxnet flag.
Containers can be started without that flag and later joined to a network...

create a container in one command: docker run --hostname nodeapp7 name nodeapp7 -d nodebox
join the network in another command: docker network connect nxnet nodeapp7

Also, these containers do not expose ports! These containers will only "talk to" the nginx container, and the nginx container will be accessible from the host machine.

The NGINX containers

docker run --name nxproxy --hostname ng1 -p 8081:8081 --network nxnet -v $PWD/nginx.conf:/etc/nginx/nginx.conf nginx:alpine
docker run --name nxproxy --hostname ng2 -p 8082:8082 --network nxnet -v $PWD/nginx2.conf:/etc/nginx/nginx.conf nginx:alpine

Note the volume mounts: the configs file made earlier gets mounted to the default location in the container, /etc/nginx/nginx.conf.

Test The Setup

use a browser and go to localhost:8081.
This will connect to nginx, which passes the request, round-robin, to the 3 instances of the node api.
The UI should show Hello from ______.
Refreshing the page should show "rotating" values in the Hello from ______ - 3 different values.
This rotation of values illustrates that nginx is having the 3 instances of the node server "handle" the requests and responses, as the 3 rotating values represent the 3 "hosts" of each docker container.
use a browser and go to localhost:8082 - the same "rotating" output should exist :)

Tags:

nginx