Rede Bridge na prática

Laboratório

3 redes por padrão:

$ docker network ls
NETWORK ID     NAME      DRIVER    SCOPE
4fd474dd0ebe   bridge    bridge    local
73f2d51a39de   host      host      local
9198ba9fc6fd   none      null      local

Inspeção da rede bridge:

$ docker network inspect 4fd474dd0ebe
[
    {
        "Name": "bridge",
        "Id": "4fd474dd0ebe7aad9a3d19048b4544eca0dd2642bee8f6b0ceb3e1dbbead1824",
        "Created": "2024-08-27T08:18:12.74665459-03:00",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": [
                {
                    "Subnet": "172.17.0.0/16",
                    "Gateway": "172.17.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {},
        "Options": {
            "com.docker.network.bridge.default_bridge": "true",
            "com.docker.network.bridge.enable_icc": "true",
            "com.docker.network.bridge.enable_ip_masquerade": "true",
            "com.docker.network.bridge.host_binding_ipv4": "0.0.0.0",
            "com.docker.network.bridge.name": "docker0",
            "com.docker.network.driver.mtu": "1500"
        },
        "Labels": {}
    }
]

Os container criados, por padrão, são inseridos na rede bridge.

Por exemplo:

$ docker container run -d nginx
Unable to find image 'nginx:latest' locally
latest: Pulling from library/nginx
e4fff0779e6d: Pull complete
2a0cb278fd9f: Pull complete
7045d6c32ae2: Pull complete
03de31afb035: Pull complete
0f17be8dcff2: Pull complete
14b7e5e8f394: Pull complete
23fa5a7b99a6: Pull complete
Digest: sha256:447a8665cc1dab95b1ca778e162215839ccbb9189104c79d7ec3a81e14577add
Status: Downloaded newer image for nginx:latest
5c428ec1a30f3e18fb0ac7433fcec9f4e562aa0410e6002aaf6796a207ac7f31

$ docker container ls
CONTAINER ID   IMAGE     COMMAND                  CREATED          STATUS          PORTS     NAMES
5c428ec1a30f   nginx     "/docker-entrypoint.…"   25 seconds ago   Up 24 seconds   80/tcp    jolly_albattani

$ docker container inspect 5c428ec1a30f | grep -i network
            "NetworkMode": "bridge",
        "NetworkSettings": {
            "Networks": {
                    "NetworkID": "4fd474dd0ebe7aad9a3d19048b4544eca0dd2642bee8f6b0ceb3e1dbbead1824",

$ docker container inspect 5c428ec1a30f | grep -i gateway
            "Gateway": "172.17.0.1",
            "IPv6Gateway": "",
                    "Gateway": "172.17.0.1",
                    "IPv6Gateway": "",
                    
$ docker container inspect 5c428ec1a30f | grep -i ipaddress
            "SecondaryIPAddresses": null,
            "IPAddress": "172.17.0.2",
                    "IPAddress": "172.17.0.2",                    

Outro exemplo:

$ docker container run -it ubuntu /bin/bash
Unable to find image 'ubuntu:latest' locally
latest: Pulling from library/ubuntu
31e907dcc94a: Already exists
Digest: sha256:8a37d68f4f73ebf3d4efafbcf66379bf3728902a8038616808f04e34a9ab63ee
Status: Downloaded newer image for ubuntu:latest
root@4b2a2198ec89:/#

$ docker container ls
CONTAINER ID   IMAGE     COMMAND                  CREATED          STATUS          PORTS     NAMES
4b2a2198ec89   ubuntu    "/bin/bash"              33 seconds ago   Up 32 seconds             charming_wilbur

$ docker container inspect 4b2a2198ec89 | grep -i network
            "NetworkMode": "bridge",
        "NetworkSettings": {
            "Networks": {
                    "NetworkID": "4fd474dd0ebe7aad9a3d19048b4544eca0dd2642bee8f6b0ceb3e1dbbead1824",
                    
$ docker container inspect 4b2a2198ec89 | grep -i gateway
            "Gateway": "172.17.0.1",
            "IPv6Gateway": "",
                    "Gateway": "172.17.0.1",
                    "IPv6Gateway": "",   
                    
$ docker container inspect 4b2a2198ec89 | grep -i ipaddress
            "SecondaryIPAddresses": null,
            "IPAddress": "172.17.0.3",
                    "IPAddress": "172.17.0.3",                                                      

Os 2 containers foram inseridos na mesma rede com o modo bridge:

Instalar o curl no container em que o Ubuntu está sendo executado e acessar o NgINX que está sendo executado no outro container:

root@4b2a2198ec89:/# apt update && app install curl --yes
root@4b2a2198ec89:/# curl http://172.17.0.2
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

O container é efêmero. Trabalhar com endereço IP no container é errado.

Simulação de cenário com a exclusão do container do NgINX e a criação de novos containeres (i.e., hello-world, conversao-temperatura, nginx etc.):

$ docker container ls
CONTAINER ID   IMAGE     COMMAND                  CREATED        STATUS          PORTS     NAMES
4b2a2198ec89   ubuntu    "/bin/bash"              23 hours ago   Up 59 seconds             charming_wilbur
5c428ec1a30f   nginx     "/docker-entrypoint.…"   23 hours ago   Up 1 second     80/tcp    jolly_albattani
$ docker container rm -f 5c428ec1a30f
5c428ec1a30f
$ docker container ls
CONTAINER ID   IMAGE     COMMAND       CREATED        STATUS              PORTS     NAMES
4b2a2198ec89   ubuntu    "/bin/bash"   23 hours ago   Up About a minute             charming_wilbur
$ docker container run -d hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
c1ec31eb5944: Pull complete
Digest: sha256:53cc4d415d839c98be39331c948609b659ed725170ad2ca8eb36951288f81b75
Status: Downloaded newer image for hello-world:latest
8eea478c3a607487fb35456465dcc06473ce8c0917afd8b44f109a913e8a84f5
$ docker container run -d marcelodpbarbieri/conversao-temperatura:v1
Unable to find image 'marcelodpbarbieri/conversao-temperatura:v1' locally
v1: Pulling from marcelodpbarbieri/conversao-temperatura
31e907dcc94a: Already exists
2b84bdeb597a: Pull complete
f0392a7398c4: Pull complete
f41b53d4e76c: Pull complete
8dadaaf7622a: Pull complete
Digest: sha256:1fa5eb0aecb5e46bc7ed3e01f3ee9e3c8fb7336f9fea64b8839690825d1fa11b
Status: Downloaded newer image for marcelodpbarbieri/conversao-temperatura:v1
0682a0a0f8017ace97f71d82177a3849d978758c9d022d4da95a9b68eeb4c643
$ docker container run -d nginx
c50920d72e98bb580168c73dbd21eeffd21eccd59acb7227b2386fb483d11cd9

Inspecionar o endereço IP do container NgINX para verificar que o endereço IP não é o mesmo. Antes era 172.17.0.2 e agora é 172.17.0.4:

$ docker container inspect c50920d72e98bb580168c73dbd21eeffd21eccd59acb7227b2386fb483d11cd9 | grep
 -i ipaddress
            "SecondaryIPAddresses": null,
            "IPAddress": "172.17.0.4",
                    "IPAddress": "172.17.0.4",

O acesso ao container antes parametrizado com o endereço IP 172.17.0.2 não está mais acessível:

$ docker container exec -it 4b2a /bin/bash
root@4b2a2198ec89:/# curl http://172.17.0.2
curl: (7) Failed to connect to 172.17.0.2 port 80 after 0 ms: Couldn't connect to server

Teria que ser utilizado o novo endereço IP 172.17.0.4:

root@4b2a2198ec89:/# curl http://172.17.0.4
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Apesar da rede no modo bridge ser disponibilizada pelo Docker, não deve ser utilizada. Ela não tem um DNS vinculada a ela. Ela somente trabalha com endereço IP.