Rails send request to other container [Failed to open TCP connection] - ruby-on-rails

Question

I am trying to do multiple node distribution systems by multiple Rails node + docker + MySQL + Redis.
Therefore, my main node needs to communicate with other nodes.
Here is my docker-compose.yml
**version: '2'
services:
db:
image: mysql:5.7
restart: always
environment:
- MYSQL_ROOT_PASSWORD=password
- MYSQL_DATABASE=pubsub_1_development
- MYSQL_USER=appuser
- MYSQL_PASSWORD=password
ports:
- "3308:3306"
redis:
image: 'redis:4.0-alpine'
app:
image: pubsub_2:1.0.8
command: /bin/sh -c "rm -f ./tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
volumes:
- ".:/pubsub_2"
ports:
- "3001:3000"
depends_on:
- db
- redis
- sub_node
- pub_node
links:
- db
- redis
- sub_node
- pub_node
environment:
DB_USER: root
DB_NAME: pubsub_1_development
DB_PASSWORD: password
DB_HOST: db
REDIS_CABLE_PORT: redis://redis:6379/1
SUB_NODE: 0.0.0.0:4001
PUB_NODE: 0.0.0.0:4000
stdin_open: true
tty: true
sub_node:
image: sub_node:1.0.1
command: /bin/sh -c "rm -f /sub_node/tmp/pids/server.pid && bundle exec rails s -p 4001 -b '0.0.0.0'"
ports:
- "4001:4001"
environment:
DB_USER: root
DB_NAME: pubsub_1_development
DB_PASSWORD: password
DB_HOST: db
REDIS_CABLE_PORT: redis://redis:6379/1
tty: true
expose:
- "4001"
pub_node:
image: pub_node:1.0.1
command: /bin/sh -c "rm -f /pub_node/tmp/pids/server.pid && bundle exec rails s -p 4000 -b '0.0.0.0'"
ports:
- "4000:4000"
environment:
DB_USER: root
DB_NAME: pubsub_1_development
DB_PASSWORD: password
DB_HOST: db
REDIS_CABLE_PORT: redis://redis:6379/1
tty: true
expose:
- "4000"**
However, when I try to use app node to send the request to pub_node, it threw this error.
Errno::ECONNREFUSED: Failed to open TCP connection to 127.0.0.1:4000 (Connection refused - connect(2) for "127.0.0.1" port 4000)
from /usr/local/lib/ruby/2.5.0/net/http.rb:939:in `rescue in block in connect'
I was doing post by this code.
rvlist = '127.0.0.1:4000'
HTTParty.post("http://#{rvlist}/publish", options)
It works in my development mode without the docker environment.

Answer 1

Networking in docker-compose:
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.
Reference: https://docs.docker.com/compose/networking/
In your case, any container within docker-compose can open the TCP connection to pub_node container using its container name and port pub_node:4000