ping from docker container cannot reach outside hosts - docker

Question

I am trying to ping from a docker container running along with other services controlled with docker-compose.
Basic requirement is to connect to external db servers, which is not working. To debug I tried to ping the external box, which as expected don't return. I can however ping the external box from vm host.
The /etc/hosts has entry as I have provided following line in docker-compose.yml
extra_hosts:
- "externalhostname:10.40.154.27"
From docker inspect the following is the network details
"Networks": {
"echo_service_default": {
"IPAMConfig": null,
"Links": null,
"Aliases": [
"python-interpreter",
"3767f3a7ad80"
],
"NetworkID": "10ca2ec9a1dbc3659cef91014c2c64c8df17e9d720350d1bdd198a53c6c0a946",
"EndpointID": "c920443c34ff00ffefe2c669bc4b80e121c27d1b8ebc44fa9f5efb16e71561a4",
"Gateway": "172.19.0.1",
"IPAddress": "172.19.0.6",
"IPPrefixLen": 16,
"IPv6Gateway": "",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"MacAddress": "02:42:ac:13:00:06",
"DriverOpts": null
}
ifconfig in host gives
docker0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
inet 172.17.0.1 netmask 255.255.0.0 broadcast 172.17.255.255
inet6 fe80::42:b6ff:fe86:fb71 prefixlen 64 scopeid 0x20<link>
ether 02:42:b6:86:fb:71 txqueuelen 0 (Ethernet)
RX packets 204 bytes 90455 (88.3 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 5080 bytes 459752 (448.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
The service entry from docker-compose.yml
python-interpreter:
image: image name
hostname: python-interpreter
volumes:
- /scratch/share:/var/python-interpreter/data:ro
- shared:/var/shared
extra_hosts:
- "externalhostname:10.40.154.27"
so the service is running with bridge network with no -p option

Answer 1

In the docker-compose.yml you shared, the python-interpreter service has a extra_hosts definition but not a network definition, you need to define a network, for example:
python-interpreter:
image: image name
hostname: python-interpreter
volumes:
- /scratch/share:/var/python-interpreter/data:ro
- shared:/var/shared
networks:
- backend
And define the network at the end of your docker-compose.yml :
networks:
backend:
driver: bridge

Answer 2

it seems it is working now..
i changed to host mode
python-interpreter:
image: ...
hostname: ...
**network_mode: host**
volumes:
...
extra_hosts:
- "whf00aqw.in.oracle.com:10.40.154.27"
I believe (not sure.)because it was going to bridge , it was restricting network access to within host. Now that i have made it host , it is able to share host network and able to access.