Docker container communication on the same net not work - docker

Question

I have 3 different docker container (on windows 10) on the same network (core_net), but when use curl on backend
-curl localhost:7000
the response is:
"curl: (7) Failed to connect to localhost port 7000: Connection refused"
Why?
Docker commands:
Frontend:
docker run -itd --name dam --net=core_net -p 3000:3000 DAM
Backend:
docker run -itd --name core --net=core_net -p 6000:6000 -p 7000:7000 -p 8000:8000 -p 9000:9000 SG
Database:
docker run --name mongodb -p 27017:27017 -d mongo:3
These is the dockerfile:
Frontend:
FROM node:4.5.0
# Create app directory
RUN mkdir -p /DAM
WORKDIR /DAM
# Install app dependencies
COPY package.json /DAM
RUN npm install
RUN npm install gulp -g
RUN echo '{ "allow_root": true }' > /root/.bowerrc
RUN npm install bower -g
# Bundle app source
COPY . /DAM
ENV PORT 3000 3001
EXPOSE $PORT
CMD ["gulp", "serve"]
and
Backend:
FROM node:4.5.0
RUN npm install nodemon -g
# Create app directory
RUN mkdir -p /SG
WORKDIR /SG
# Install app dependencies
COPY package.json /SG
RUN npm install
# Bundle app source
COPY . /SG
ENV PORT 6000 7000 8000 9000
EXPOSE $PORT
CMD ["npm", "start"]
Inside container the ping works and the inspect is this:
$ docker network inspect core_net
{
"Name": "core_net",
"Id": "1f9e5426abe397d520360c05c95fee46fe08c98fe5c474c8b52764e491ea23e7",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": {},
"Config": [
{
"Subnet": "172.18.0.0/16",
"Gateway": "172.18.0.1"
}
]
},
"Internal": false,
"Containers": {
"3d3b8780fba2090b1c2feaddf2e035624529cf5474ad4e6332fe7071c0acbd25": {
"Name": "core",
"EndpointID": "f0a6882e690cf5a7deedfe57ac9b941d239867e3cd58cbdf0ca8a8ee216d53a9",
"MacAddress": "02:42:ac:12:00:04",
"IPv4Address": "172.18.0.4/16",
"IPv6Address": ""
},
"bb6a6642b3a7ab778969f2e00759d3709bdca643cc03f5321beb9b547b574466": {
"Name": "dam",
"EndpointID": "b42b802e219441f833d24971f1e1ea74e093f56e28126a3472a44750c847daa4",
"MacAddress": "02:42:ac:12:00:02",
"IPv4Address": "172.18.0.2/16",
"IPv6Address": ""
},
"cf8dd2018f58987443ff93b1e84fc54b06443b17c7636c7f3b4685948961ba3f": {
"Name": "mongodb",
"EndpointID": "be02d784cbd46261b7a53d642102887cafa0f880c8fe08086b9cc026971ea1be",
"MacAddress": "02:42:ac:12:00:03",
"IPv4Address": "172.18.0.3/16",
"IPv6Address": ""
}
},
"Options": {},
"Labels": {}
}
Commnication between mongodb and core work but between dam and core not work.
what's the problem?

Answer 1

To connect to another container with in an network you can not use localhost, but cou can use the name of the conatiner you want to reach. e.g. curl core:7000
To use localhost the conatiners have to share their network stack. You can do that with --network container:core
And if you dont have to reach the backend from outside of docker, it is enought to only expose the ports, and not to publish them