Network

• Networks are also easy concept, we are not going to learn new stuff here.
• We will just learn how to do same stuff, but more efficiently.
• But at the end you will create an app that talks with database.
• And most of all database values will be persisted.

Setting Up Network

• If you were paying attention to logs when we run our services, you saw that docker-compose creates a default network for us.
• So all services defined on same file are already in same ( default ) network.

version: '3'
services:
  myApp:
    image: amantuladhar/docker-kubernetes:v1-web
    ports:
      - 9090:8080
  myTester:                               # 1
    image: amantuladhar/network-tools     # 2
    command: sleep 50000                  # 3
  myDb:
    image: mysql:5.7
...
...

• #1 Define one more service myTester
• #2 Use the image amantuladhar/network-tools. Remember when we learned networks, we used this to test connection between two containers.
• #3 Overriding default command for an image, as this image doesn't have long-running process. This is so that it runs for a long period of time, and we can go inside the service and test our network.
• I believe this is nothing new, we already did this before.
• Only difference is that, now we are using compose, and it's convenience.

Testing Network

• Attach pseudo-tty of myTester.

docker-compose exec myTester sh

• Test the network like we did before.
• We have to use service_name to communicate with other container.
• localhost will not work. We will learn how we can achieve this later.

/ # curl myApp:8080/test | jq .
{
  "message": "Hello Fellas!!!",
  "host.address": "192.168.48.2",
  "app.version": "v1-web"
}

Named Network

• While relying on default network works, you may want to name your network yourself.
• You may even want to create multiple networks.
• To achieve that we have networks root properties.
• If we use it as a root property, we can define any number custom networks we want.
• If used inside services property, it will make that particular service reside in the network.

version: '3'
services:
  myApp:
    image: amantuladhar/docker-kubernetes:v1-web
    ports:
      - 9090:8080
    networks:                              # 3     
      - myNet                              # 4    
  myTester:
    image: amantuladhar/network-tools
    command: sleep 50000
    networks:                              # 3    
      - myNet                              # 4    
  myDb:
    image: mysql:5.7
...
...
networks:                                  # 1
  myNet:                                   # 2
...
... 

• #1 this is a root property. This includes list of custom network you want to create.
• #2 name of network you want to create.
• #3 this is used inside services. This defines which network particular service communicates with.
• #4 Name of networks service will use. You can add multiple networks
• You can check if two containers can talk with each other like before.

Using network_mode

• With help of network_mode property we can define the way container network are configured.
• Remember --net=container:@name syntax. network_mode can achieve something like this.
• network_mode supports
  • "bridge"
  • "host"
  • "none"
  • "service:@name"
  • "container:@id/@name"
• For now, we will use serrvice:@name mode. Which I think will often be used than others.

version: '3'
services:
  myApp:
    image: amantuladhar/docker-kubernetes:v1-web
    ports:
      - 9090:8080
    networks:                                   
      - myNet                                 
  myTester:
    image: amantuladhar/network-tools
    command: sleep 50000
    network_mode: service:myApp           # 1
  myDb:
    image: mysql:5.7
...
...
...

• #1 This defines that we want to use same network that is being used by service myApp.
• We are using networks properties for **myApp**, to define network for service.
• Notice we didn't even have to define networks properties for myTester.
• When defining a service you cannot use ports and network_mode properties at the same time.
• Testing using localhost in myTester

/ # curl localhost:8080/test
{
"message": "Hello Fellas!!!",
"host.address": "192.168.112.2",
"app.version": "v1-web"
}

Web App With Database

• You now have knowledge of how docker-compose and its component works.
• Let's create a web app that connects with database.
• You can use amantuladhar/docker-kubernetes:v1-db image to get the app that tries to connect with database.
  • This tag expects three environment variable: DB_URL, DB_USER, DB_PASS.
• Web App With Database Example branch compose-db-initial if you want to build it yourself.
• Here's a compose file we are initially working with

version: '3'
services:
  myApp:
    image: amantuladhar/docker-kubernetes:v1-db
    ports:
      - 9090:8080
  myDb:
    image: mysql:5.7
    environment:
      - MYSQL_ROOT_PASSWORD=password
      - MYSQL_DATABASE=docker_kubernetes
    volumes:
      - "./volume/mysql-compose/:/var/lib/mysql/"
networks:
  myNet:

• First step is to add network on both the services. (Or you can use default network).

version: '3'
services:
  myApp:
    image: amantuladhar/docker-kubernetes:v1-db
    ports:
      - 9090:8080
    networks:                                 # 1
      - myNet                                 # 1
  myDb:
    image: mysql:5.7
    networks:                                 # 1
      - myNet                                 # 1
    environment:
      - MYSQL_ROOT_PASSWORD=password
      - MYSQL_DATABASE=docker_kubernetes
    volumes:
      - "./volume/mysql-compose/:/var/lib/mysql/"
networks:
  myNet:

• #1 added network to our services.
• If you are using image above, it expected three stuff so that it can successfully connect with database.
  • DB_URL Connection URL
  • DB_USER Database User
  • DB_PASS Database User Password

version: '3'
services:
  myApp:
    image: amantuladhar/docker-kubernetes:v1-db
    ports:
      - 9090:8080
    networks:
      - myNet
    environment:                                                       # 1
      - DB_URL=jdbc:mysql://myDb:3306/docker_kubernetes?useSSL=false   # 2
      - DB_USER=root                                                   # 2
      - DB_PASS=password                                               # 2   
  myDb:
    image: mysql:5.7
    networks:
      - myNet
    environment:
      - MYSQL_ROOT_PASSWORD=password
      - MYSQL_DATABASE=docker_kubernetes
    volumes:
      - "./volume/mysql-compose/:/var/lib/mysql/"
networks:
  myNet:

• #1 Using environment property to set our environment variable.
• #2 Setting necessary environment variables.
• If you run the services now you should be able to start your app and run it.

Managing service start order

• When using above compose file, it is not necessary that database starts first and web later.
• Docker compose doesn't know which service to start first.
• If our web app starts first and then database, clearly our app will fail.
• To minimize such issues docker-compose has depends_on property that we can use.
• We can add list of services particular service depends on and docker-compose will take care of starting them in order.

depends_on does not wait for mysql to be ready before starting web only until they have been started.

version: '3'
services:
  myApp:
    image: amantuladhar/docker-kubernetes:v1-db
...
...
    depends_on:            <-------------
      - myDb
  myDb:
    image: mysql:5.7
    networks:
      - myNet
...
...
networks:
  myNet: