docker-compose connect server/client containers from different devices on LAN - docker

Question

I am using docker-compose for deploying a server/client application on different devices on my local network. My setting is the following:
In my docker-compose.yml file, I have a service called 'server', which depends on two additional services ('database' and 'web'). These three services are running on the same device and are able to connect successfully with each other. The 'server' service deploys a Flask-based API which should ideally be waiting for requests from other devices in the same LAN.
In the very same docker-compose.yml file, I have a service called 'client', which runs an application that should be deployed on more than one device in the same LAN. The 'client' service, independently from the device where it is running, should be able to send requests to the 'server' service, which is on a different device in the same LAN.
Here is my docker-compose.yml file:
version: '3.5'
networks:
outside:
driver: bridge
ipam:
driver: default
config:
- subnet: 192.168.220.0/24
services:
client:
build: ./client
environment:
TZ: "Europe/Madrid"
command: >
sh -c "ln -snf /usr/share/zoneinfo/$TZ /etc/localtime &&
echo $TZ > /etc/timezone &&
nmap -p 8080 192.168.220.220 &&
python -u client/main_controller.py"
restart: always
volumes:
- .:/code
networks:
outside:
server:
build: ./server
environment:
TZ: "Europe/Madrid"
command: >
sh -c "ln -snf /usr/share/zoneinfo/$TZ /etc/localtime &&
echo $TZ > /etc/timezone &&
python -u server/main_server.py"
volumes:
- .:/code
ports:
- "8080:8080" # host:container
restart: always
depends_on:
- database
- web
networks:
default:
outside:
ipv4_address: 192.168.220.220
database:
image: mysql:latest
#command: ./database/run_db.sh #mysqld --user=root --verbose
restart: always
volumes:
- ./database:/docker-entrypoint-initdb.d/:ro
ports:
- "3306:3306" # host:container
environment:
MYSQL_ROOT_PASSWORD: root
networks:
default:
web:
image: nginx:latest
restart: always
ports:
- "8081:80"
volumes:
- ./interface:/www
- ./interface/nginx.conf:/etc/nginx/conf.d/default.conf
networks:
default:
I am using the python requests library to send requests from 'client' to 'server' using the following url:
http://192.168.220.220:8080
My issue is, that when I run both containers, 'client' and 'service', on the same device [deviceA], they are able to successfully communicate.
But when I run the containers on different devices ('service' on a computer with Mac OS X [deviceA], and 'client' on a Raspberry Pi [deviceB], both connected to the same LAN using wi-fi), the 'client' is not able to reach the specified IP and port.
To test if the device is able to reach the IP:port combination I use the following command right after running the 'client' service:
nmap -p 8080 192.168.220.220
Which gives the following output on [deviceA]:
client_1 | Starting Nmap 7.01 ( https://nmap.org ) at 2019-03-03 12:22 Europe
client_1 | Nmap scan report for raspberry_escape_controller_server_1.raspberry_escape_controller_outside (192.168.220.220)
client_1 | Host is up (0.00012s latency).
client_1 | PORT STATE SERVICE
client_1 | 8080/tcp open http-proxy
client_1 | MAC Address: <mac_address> (Unknown)
client_1 |
client_1 | Nmap done: 1 IP address (1 host up) scanned in 0.71 seconds
and the following one on [deviceB]:
client_1 | Starting Nmap 7.40 ( https://nmap.org ) at 2019-03-03 13:24 CET
client_1 | Note: Host seems down. If it is really up, but blocking our ping probes, try -Pn
client_1 | Nmap done: 1 IP address (0 hosts up) scanned in 0.78 seconds
----------- [EDIT 1] -----------
As suggested by DTG here is the output of netstat command on [deviceB]:
root#a9923f852423:/code# netstat -nr
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
0.0.0.0 192.168.220.1 0.0.0.0 UG 0 0 0 eth0
192.168.220.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
It looks like it is not able to see [deviceA], which should be 192.168.220.220

Answer 1

It looks to me that even though the service is up and running in your [deviceA] , there is some kind of firewall not allowing external connections to it from outside .
Maybe you should need to check the Firewall configuration at [deviceA].
ROUTING ISSUES
If it is a Routing issue you should see the routing table in hostB with
netstat -nr
And see that a valid route exist to hostA
If no valid route exist you should add one with
sudo route add -net hostA_IP/MASK gw HOSTB_DEFAULT_GATEWAY
INTER DOCKERS COMUNICATIONS
After you create the network, you can launch containers on it using the docker run --network= option. The containers you launch into this network must reside on the same Docker host. Each container in the network can immediately communicate with other containers in the network.
Read more about understanding docker communications:
See docker documentation here