Docker Cannot Resolve Hostname - docker

Question

I am trying to link my containerized VueJS frontend with my containerized Spring Boot API backend, with great difficulty.
Whenever I try to make an HTTP request to my API using the container name, I get the following.
OPTIONS http://api:4505/user/sign-in net::ERR_NAME_NOT_RESOLVED
Here is my docker-compose file:
version: "3"
services:
mongodb:
image: mongo
container_name: mongo
ports:
- "27017:27017"
api:
image: registry.gitlab.com/darragh.oflah/api:latest
container_name: api
ports:
- "4505:4505"
links:
- mongodb
web:
image: registry.gitlab.com/darragh.oflah/web:latest
container_name: web
ports:
- "80:8080"
links:
- api
Here what I get when I run sudo docker network inspect tmp_default
So it would seem that the network is set up correctly
[
{
"Name": "tmp_default",
"Id": "75ab7c89cb5a80aa7eddd7c5a3f7f4aafb911cfe96a923ad3db2219552366fd7",
"Created": "2020-02-04T16:55:49.131485109Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "172.18.0.0/16",
"Gateway": "172.18.0.1"
}
]
},
"Internal": false,
"Attachable": true,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"6ae3db08be2ed22245a173a677ae1b0f28eca878aa84e43744a320589cbda5af": {
"Name": "mongo",
"EndpointID": "b399bb72f28b6d47a93927712a665dcc725d27a6ba2ee432e715db00c9cbc835",
"MacAddress": "02:42:ac:12:00:02",
"IPv4Address": "172.18.0.2/16",
"IPv6Address": ""
},
"fa7e4066e436181ce2991e048790f8de518af31fb97cf9351316ff8f41824449": {
"Name": "api",
"EndpointID": "bf8d071683bfa4ecbd215f3dd534d0e278702ed4377552ef242e5c65b01c3fa1",
"MacAddress": "02:42:ac:12:00:03",
"IPv4Address": "172.18.0.3/16",
"IPv6Address": ""
},
"fb544ef5389afd74d53f45d6de968008632b65340f161527a9c7aa4214aa7674": {
"Name": "web",
"EndpointID": "2dc3e8a452c241916a2e9f7e25b33ee7997fe2d25ec3543e5d34e888e50d905c",
"MacAddress": "02:42:ac:12:00:04",
"IPv4Address": "172.18.0.4/16",
"IPv6Address": ""
}
},
"Options": {},
"Labels": {
"com.docker.compose.network": "default",
"com.docker.compose.project": "tmp",
"com.docker.compose.version": "1.21.2"
}
}
]
In the net work tab, the request is saying failed, which would indicate to me that the request is failing to leave the container at all.

Answer 1

Your compose file creates a docker network. You're running "web" in a container on that network. All containers in the docker network can access other containers via the hostname. However, the browser is running on your host machine. Your host machine is not in the docker network. Therefore your browser won't be able to access the api container via the hostname. If you type http://api:4505/user/sign-in into the browser url bar, it's doing the same thing, and you'll also get an error.