Docker networking on windows IP confusion - windows

Question

I'm new to Docker and things are a bit confusing so far.
I ran these containers and they work just fine.
docker network inspect dockersymfony_default tells the IP of nginx container is 172.19.0.5. I can access nginx with this IP from other containers in network (php, db, ...).
BUT from the host machine (Windows) nginx container is not accessible by 172.19.0.5. On the other hand nginx is accessible by 127.0.0.1 or localhost.
[
{
"Name": "dockersymfony_default",
"Id": "12b4f5a663450bb44e87f9635860bbcede354f2fea27f93b056d7159251dc465",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "172.19.0.0/16",
"Gateway": "172.19.0.1"
}
]
},
"Internal": false,
"Containers": {
"1eef50ee350782654bb96e7d16d09e3b9fe54abca97cc339a89791083e08563c": {
"Name": "dockersymfony_db_1",
"EndpointID": "8b48ea4934a01703ac23a7f27f8cee0ff9226b7b5401550859b22fbf17a4c10a",
"MacAddress": "02:42:ac:13:00:03",
"IPv4Address": "172.19.0.3/16",
"IPv6Address": ""
},
"1faf199dd6285c6700640b570fd842212962c299d762c531b011205f58598102": {
"Name": "dockersymfony_nginx_1",
"EndpointID": "a9be2a542565262d31c93f7d1960a13e373f5a701c299cedf3dc0510c8de9bf4",
"MacAddress": "02:42:ac:13:00:05",
"IPv4Address": "172.19.0.5/16",
"IPv6Address": ""
},
"2c2b994c92895e7a83c189d1e5002d2eb7d88f62761f8c324f00ffdece4efb4a": {
"Name": "dockersymfony_php_1",
"EndpointID": "98a0ad7bef2f2c963c68561bb2b56bc0feb113c390a29c0dd9aefd6e32b7e5be",
"MacAddress": "02:42:ac:13:00:04",
"IPv4Address": "172.19.0.4/16",
"IPv6Address": ""
},
"65ee8088e6bc2405b80c56ae21d83a4f4f7fff252a7e782c4046629d670f7b74": {
"Name": "dockersymfony_redis_1",
"EndpointID": "80fcd76b2fe0326be8d30abaffe2310ef58f23935f0f67f7476fa4fad951cba6",
"MacAddress": "02:42:ac:13:00:02",
"IPv4Address": "172.19.0.2/16",
"IPv6Address": ""
},
"86665f35aa1599028d8e91aa45f86505a112b44496386e674b7039458dcda45f": {
"Name": "dockersymfony_elk_1",
"EndpointID": "c82ef8cc18f1cc345e97c3bdd0e04f0bf398efc0c38f9876b0e922a1e6dd494c",
"MacAddress": "02:42:ac:13:00:06",
"IPv4Address": "172.19.0.6/16",
"IPv6Address": ""
}
},
"Options": {},
"Labels": {}
}
]
Why is that ?
I suppose that this problem is the cause of another one: xdebug doesn't work.

Answer 1

The containers in the project you linked to are Linux containers. Docker on Windows runs Linux containers inside a Linux VM it creates using Hyper-V. Assuming you started those containers using the docker-compose file in the project, they will all be attached to default bridge network. I found this description of the docker0 bridge helpful
By default, the Docker server creates and configures the host system’s docker0 interface as an Ethernet bridge inside the Linux kernel that can pass packets back and forth between other physical or virtual network interfaces so that they behave as a single Ethernet network.
Since the containers are all attached to the same network, they are all able to access each other by IP address. If you were able to connect to the VM that Docker for Windows creates, you would be able to access those containers by their IP addresses as well.
The nginx container is accessible from localhost and from 127.0.0.1 because of port binding. When you create a container and publish (as the docker-compose file does on this line), Docker for Windows does some magic1 and requests made on that port are forwarded to the VM that's running your containers, that VM then forwards the request to the container running nginx, which then responds to the request and you see the response in the browser.
1. Not actually magic