Couldn't connect to service inside docker container - docker

Question

I try to run command inside docker container like this:
openssl s_client -connect 127.0.0.1:4443
CONNECTED(00000003)
in the next step I try to detect ip for docker image from /etc/hosts:
172.18.0.2 aaf6fa11bc88
then I try to connect inside containers to this IP and got:
openssl s_client -connect 172.18.0.2:4443
connect: Connection refused
not sure why I could connect to 127.0.0.1 and couldn't connect by IP 172.18.0.2 which has been placed in /etc/hosts file in Docker container?
I have flashed iptables:
iptables -F and iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
There is ifconfig output:
ifconfig
eth0 Link encap:Ethernet HWaddr 02:42:ac:12:00:02
inet addr:172.18.0.2 Bcast:172.18.255.255 Mask:255.255.0.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:9028 errors:0 dropped:0 overruns:0 frame:0
TX packets:5038 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:12755512 (12.1 MiB) TX bytes:278694 (272.1 KiB)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:48 errors:0 dropped:0 overruns:0 frame:0
TX packets:48 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1
RX bytes:5332 (5.2 KiB) TX bytes:5332 (5.2 KiB)
app is running inside container:
ps ax
PID TTY STAT TIME COMMAND
1 ? Ss 0:01 python db_adapter.py
284 pts/0 Ss 0:00 /bin/bash
315 pts/0 R+ 0:00 ps ax
I couldnt connect to db_adapter using ip like 172.18.0.2 but could connect to 127.0.0.1 (maybe problem with db_adapter?)
There is output :
docker-compose ps
Name Command State Ports
-------------------------------------------------------------------------------------
docker_db-adapter_1 python db_adapter.py Up 0.0.0.0:4443->4443/tcp
There is docker-compose file:
version: '2'
services:
fake-s3:
image: fake-s3
db-adapter:
image: db-adapter
ports:
- "4443:4443"
mail:
image: mail
volumes:
depends_on:
- fake-s3
- db-adapter
links:
- db-adapter
volumes:
mailproxy:

Answer 1

Your python application db-adapter binds only to localhost. That's why you can access it only via 127.0.0.1:4443 and only inside a container. You need to find a way to bind it to 0.0.0.0. After that you can access it on 172.18.0.2:4443 inside container and by 127.0.0.1:4443 from host.