Connect docker container to internet - linux

Question

I have created my docker image and container using the Dockerfile in this blog.
https://hackernoon.com/raspberry-pi-cluster-emulation-with-docker-compose-xo3l3tyw
I am able to ssh into the rpi and ifconfig returns the following status:
pi#raspberrypi:~ $ ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.0.2.15 netmask 255.255.255.0 broadcast 10.0.2.255
ether 52:54:00:12:34:56 txqueuelen 1000 (Ethernet)
RX packets 561 bytes 49862 (48.6 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 386 bytes 47311 (46.2 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
device interrupt 41 base 0x1000 dma 0xff
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
loop txqueuelen 1000 (Local Loopback)
RX packets 2 bytes 100 (100.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 2 bytes 100 (100.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
Now I want to be able to connect this to internet. As per docker docs, I tried to connect a running container to the internet using:
docker network connect multi-host-network 008796f5316a
It returns the error.
Error response from daemon: network multi-host-network not found.
How can I connect to the internet from inside the docker?
Edit:
The blog talks about running qemu on docker and installing a modified raspbian on top of that(for compatibility with qemu).
When I access the container using docker exec command,
docker exec -it testnode bash
ifconfig returns the following:
root#1f210520938c:~# ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.17.0.2 netmask 255.255.0.0 broadcast 172.17.255.255
ether 02:42:ac:11:00:02 txqueuelen 0 (Ethernet)
RX packets 637 bytes 356778 (356.7 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 404 bytes 39482 (39.4 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
loop txqueuelen 1000 (Local Loopback)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
And the ifconfig command for pi returns the results as shown above.
So, ping google.com is working on the root# and not on pi#raspberry.
I need to connect the pi directly to the internet.

Answer 1

This error occurs because you haven't created a Docker network called multi-host-network. To create it, you may refer to Docker docs.
By default, all docker containers are connected to the default bridge network (the name matches driver type). As for docker-compose, bridge network with name docker-compose-directory-name_defaultwill be created, as described [here][2]. You can check it by runningdocker network inspect docker-compose-directory-name_defaultand find your container inContainers` section.
Since your container is already connected to the internet, it should have internet access without explicitly connecting it to a network.
If there is no internet connection, please try solutions proposed in this question. I would suggest starting with
sysctl -w net.ipv4.ip_forward=1 # both on host and container
sudo service docker restart # (or sudo systemctl restart docker) on host

Answer 2

The instructions you're following set up QEMU to use "user-mode networking". This is (sort of) like QEMU itself emulating a little NAT-router and private network that the VM lives behind. This in turn is inside the docker container and talking to whatever the docker container's networking setup is, so you have two layers here -- you'll want to be clear about this double-layer setup so you don't get confused about which of the two might be the source of any problems you have.
User-mode networking has some limitations: notably, ping doesn't work, and you can't connect from the outside into the VM except where you have specific port-forwarding set up (the instructions include a port-forward from host port 2222 to the VM's ssh port 22).
So you need to figure out whether you can live with user-mode networking's limits, and make sure that whatever testing you're doing is testing what you care about and not things you probably don't really care about like whether ping packets in particular work. If you don't want user-mode networking, you'll need to set up a QEMU tap (bridge) network backend, which is a lot more complicated but does let you make a QEMU VM truly visible as a machine on the host network.