Networking Overview in Compose file

Hai semuanya di materi kali ini kita akan membahas tentang Networking menggunakan Docker Compose

By default Compose sets up a single network for your app. Each container for a service joins the default network and is both reachable by other containers on that network, and discoverable by them at a hostname identical to the container name.

For example, suppose your app is in a directory called myapp, and your docker-compose.yml looks like this:

When you run docker-compose -p myapp up, the following happens:

1. A network called myapp_default is created.
2. A container is created using web’s configuration. It joins the network myapp_default under the name web.
3. A container is created using db’s configuration. It joins the network myapp_default under the name db.

Look like this:

➜ docker  docker-compose -f .\09-docker-compose\network\docker-compose.yaml -p myapp up -d
Creating network "myapp_default" with the default driver
Status: Downloaded newer image for postgres:12.6
Creating myapp_webapp_1 ... done
Creating myapp_db_1     ... done

➜ docker  docker-compose -f .\09-docker-compose\network\docker-compose.yaml -p myapp ps
     Name                   Command               State                  Ports
----------------------------------------------------------------------------------------------
myapp_db_1       docker-entrypoint.sh postgres    Up      0.0.0.0:31432->5432/tcp,:::5432->5432/tcp
myapp_webapp_1   /docker-entrypoint.sh ngin ...   Up      0.0.0.0:8080->80/tcp,:::80->80/tcp

➜ docker  docker network ls -f name=myapp_default
NETWORK ID     NAME            DRIVER    SCOPE
1d8ba9a6b979   myapp_default   bridge    local

➜ docker  docker network inspect myapp_default -f '{{json .Containers}}' | python -m json.tool
{
    "06bc1e24abdb11c0fca7fc9660f17b890f5d67b06b9b3970d71839258873dcb4": {
        "Name": "myapp_webapp_1",
        "EndpointID": "b64417fe1ef6ab57b1ec22b9322fbc097e1b0e4a7a7311a58b46e224a380fecd",
        "MacAddress": "02:42:ac:12:00:02",
        "IPv4Address": "172.18.0.2/16",
        "IPv6Address": ""
    },
    "ae6570375deaf908ff225f2751b9979a1ec3279d9c66680b4715153789805514": {
        "Name": "myapp_db_1",
        "EndpointID": "c9ac8916797a4166522aad097b7807d6825e4e7bc1c03e8992d67bd3c61cbb1a",
        "MacAddress": "02:42:ac:12:00:03",
        "IPv4Address": "172.18.0.3/16",
        "IPv6Address": ""
    }
}

Each container can now look up the hostname webapp or db and get back the appropriate container’s IP address. For example, web’s application code could connect to the URL postgres://db:5432 and start using the Postgres database.

It is important to note the distinction between HOST_PORT and CONTAINER_PORT. In the above example, for db, the HOST_PORT is 31432 and the container port is 5432 (postgres default). Networked service-to-service communication uses the CONTAINER_PORT. When HOST_PORT is defined, the service is accessible outside the swarm as well.

Within the web container, your connection string to db would look like postgres://db:5432, and from the host machine, the connection string would look like postgres://{DOCKER_IP}:31432.

If you make a configuration change to a service and run docker-compose up to update it, the old container is removed and the new one joins the network under a different IP address but the same name.

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