Container networking on a single Docker host

Docker host creation

We will use Docker Machine to create our test Docker Host. Driver’s option is set to virtualbox so the host is created on the local machine as a virtualbox virtual machine.

docker-machine create --driver virtualbox node1

Get the IP of node1 docker-machine ip node1 (⇒ 192.168.99.100)

Default networks

Let’s check the networks attached to the newly created Docker host

$ eval $(docker-machine env node1)

$ docker network ls
NETWORK ID          NAME            DRIVER
d87b8fc4c466        bridge          bridge
efaf610f57a5        host            host
f7d0de539edd        none            null

By default (if no –net option is provided), Docker engine will attach each container to the bridge network (id d87b8fc4c466)

Default bridge network

Let’s run 2 container using the default bridge network (without using –net option)

$ docker run --name mongo -d mongo:3.2
$ docker run --name box -d busybox top

Make sure the containers are listed in the bridge network

$ docker network inspect --format='' d87b8fc4c466 | python -m json.tool
{
    "0b8fedf4613c7275d89861037ea1b23ad4d65ab10f16df67bf976d9cb5652311": {
        "EndpointID": "0cf0cd3b2e0438c6f68c6a1e2f7587b63c48bda74911af55d1040f0d2fb117d2",
        "IPv4Address": "172.17.0.3/16",
        "IPv6Address": "",
        "MacAddress": "02:42:ac:11:00:03",
        "Name": "mongo"
    },
    "6cb5e5f4a1bcc37925407b39f2dde41f2b370fc48a21f8289da91d17b3763a4c": {
        "EndpointID": "2a6412d3c3c25545a59ea148e317b2046965c0fe5c1eeae2c51f4f882aaa6b36",
        "IPv4Address": "172.17.0.2/16",
        "IPv6Address": "",
        "MacAddress": "02:42:ac:11:00:02",
        "Name": "box"
    }
}

Both containers appear as being linked to the bridge network but they cannot address each other by their names

$ docker run -ti busybox /bin/sh
/ # ping mongo
ping: bad address 'mongo'
/ # ping box
ping: bad address 'box'

User defined bridge network

When using user defined network, the behaviour is different than the default bridge network.

Let’s create a user defined bridge network with Docker network commands

$ docker network create mongonet
ce9ea3b69d6ee2ecf56b40bd35b8a43f8505c8ca0473bc37bdede3711ecf60c1

$ docker network ls
NETWORK ID          NAME            DRIVER
d87b8fc4c466        bridge          bridge
efaf610f57a5        host            host
ce9ea3b69d6e        mongonet        bridge
f7d0de539edd        none            null

Let’s now run 2 containers in the newly defined network

$ docker run --name mongo --net mongonet -d mongo:3.2

$ docker run --net mongonet -ti busybox /bin/sh
/ # / # ping -c 3 mongo
PING mongo (172.18.0.2): 56 data bytes
64 bytes from 172.18.0.2: seq=0 ttl=64 time=0.058 ms
64 bytes from 172.18.0.2: seq=1 ttl=64 time=0.085 ms
64 bytes from 172.18.0.2: seq=2 ttl=64 time=0.072 ms

--- mongo ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.058/0.071/0.085 ms

Containers can be addressed by their name through the DNS name server embedded in Docker 1.10+

Test our application

Run db and application containers in the new bridge network

$ docker run --name mongo --net mongonet -d mongo:3.2
$ docker run --name app --net mongonet -p 8000:1337 -d -e “MONGO_URL=mongodb://mongo/messageApp” message-app:v1

Note: MONGO_URL environment variable directly uses mongo container’s name

Test HTTP Rest API

# Create a  new message
$ curl -XPOST http://192.168.99.100:8000/message?text=hello
{
  "text": "hello",
  "createdAt": "2016-06-06T14:01:05.764Z",
  "updatedAt": "2016-06-06T14:01:05.764Z",
  "id": "57558221a4461312009ce88c"
}

# Retrieve the list of message and make sure the previous message is present
$ curl -XGET http://192.168.99.100:8000/message
[
  {
    "text": "hello",
    "createdAt": "2016-06-06T14:01:05.764Z",
    "updatedAt": "2016-06-06T14:01:05.764Z",
    "id": "57558221a4461312009ce88c"
  }
]

The application container (named app) is connected to mongo container using container name (named mongo)

Packaging of the application with Docker Compose

The following file (docker-compose.yml) defines the whole application

version: '3'
services:
  mongo:
    image: mongo:3.2
    volumes:
      - mongo-data:/data/db
    expose:
      - "27017"
  app:
    image: lucj/message-app
    ports:
      - "1337"
    links:
      - mongo
    depends_on:
      - mongo
    environment:
      - MONGO_URL=mongodb://mongo/messageApp
volumes:
  mongo-data:

The important part of this file

• Definition of 2 services
  • database service: mongo
  • application service: app
• Link between app and mongo services done through the MONGO_URL environment variable (using mongo service name)
• Port mapping
  • mongo service expose port 27017 (default MongoDB port) only to the other services (not to the Docker host)
  • app service port is mapped to a random port on the host (as no host port as been defined)
• Definition of a user defined volume for mongodb data folder

Lifecycle and scalability

The following commands are some of the main ones to interact with the application

• Start the application docker-compose up -d (-d option enables the application to run in background)
• Check the status of each services conposing the application docker-compose ps
• Stop the application docker-compose stop
• Scale the app service changing the number of instances docker-compose scale app=3

Several containers of the app service (our Node.js API) are running and are accessible through random port number of the Docker host. Wow are the new instanciated containers addressed ?

=> Need to add a load balancer that will be updated each time a container is created or removed and that will forward each request to a running instance of the app service.

Usage of dockercloud/haproxy image

dockercloud/haproxy is a good candidate to be used in front of our app service. It will update it’s configuration each time a container is started / stopped.

Adding load balancer to our Compose file

The new version of our docker-compose.yml is

version: '3'
services:
  mongo:
    image: mongo:3.2
    volumes:
      - mongo-data:/data/db
    expose:
      - "27017"
 lbapp:
    image: dockercloud/haproxy
    links:
      - app
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    ports:
      - "8000:80"
  app:
    image: message-app
    expose:
      - "1337"
    links:
      - mongo
    depends_on:
      - mongo
    environment:
      - MONGO_URL=mongodb://mongo/messageApp
volumes:
  mongo-data:

The load balancer service has been added to the picture. Each request coming to port 8000 of the host (mapped with port 80 of lbapi) will go to the api through the load balancer.

Test our application

Run the new version of our compose file and specify the number of instances of the app service

• docker-compose up
• docker-compose scale app=3

Let’s just test the creation and retrieval of a message

$ curl -XPOST http://192.168.99.100:8000/message?text=hola
{
  "text": "hola",
  "createdAt": "2016-06-08T13:30:18.298Z",
  "updatedAt": "2016-06-08T13:30:18.298Z",
  "id": "57581deacde05a1200877fa2"
}
$ curl -XGET http://192.168.99.100:8000/message
[
  {
    "text": "hola",
    "createdAt": "2016-06-08T13:30:18.298Z",
    "updatedAt": "2016-06-08T13:30:18.298Z",
    "id": "57581deacde05a1200877fa2"
  }
]

Seems to be good :)