Docker Networking Exploration

docker_networking.md

Docker networking tests

Tested on Docker 1.9+

~ > docker version
Client:
 Version:      1.9.0
 API version:  1.21
 Go version:   go1.5.1
 Git commit:   76d6bc9
 Built:        Tue Nov  3 21:17:46 UTC 2015
 OS/Arch:      darwin/amd64

Server:
 Version:      1.9.0
 API version:  1.21
 Go version:   go1.4.3
 Git commit:   76d6bc9
 Built:        Tue Nov  3 19:20:09 UTC 2015
 OS/Arch:      linux/amd64

create 2 testing docker containers

docker run -it --name test1 alpine sh
docker run -it --name test2 alpine sh

Note: they cannot communicate

In test1:

/ # ping -c 1 -W 1 test2
ping: bad address 'test2'
/ # ping -c 1 -W 1 test2.testbed
ping: bad address 'test2.testbed'

The containers cannot communicate since they are not on the same network.

/ # cat /etc/hosts
172.17.0.2  c51a702ba714
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

This is the default /etc/hosts for a container. There is no reference to other running containers.

create a network for the containers to connect to

~ > docker network create testnet
341381b9251974509a83760276b9de3c1afd9d6445b6a6bfedf76e14e0e04605

connect the containers to the network

~ > docker network connect testnet test1
~ > docker network connect testnet test2

now the containers should be able to communicate

In test1:

/ # ping test2
PING test2 (172.18.0.3): 56 data bytes
64 bytes from 172.18.0.3: seq=0 ttl=64 time=0.080 ms
64 bytes from 172.18.0.3: seq=1 ttl=64 time=0.085 ms

--- test2 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.080/0.082/0.085 ms
/ # ping test2.testbed
PING test2.testbed (172.18.0.3): 56 data bytes
64 bytes from 172.18.0.3: seq=0 ttl=64 time=0.140 ms
64 bytes from 172.18.0.3: seq=1 ttl=64 time=0.070 ms
64 bytes from 172.18.0.3: seq=2 ttl=64 time=0.069 ms

--- test2.testbed ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.069/0.093/0.140 ms

/ # nslookup test2
Server:    (null)
Address 1: ::1 localhost
Address 2: 127.0.0.1 localhost

Name:      test2
Address 1: 172.18.0.3 test2
/ # nslookup test2.testbed
Server:    (null)
Address 1: ::1 localhost
Address 2: 127.0.0.1 localhost

Name:      test2.testbed
Address 1: 172.18.0.3 test2

/ # cat /etc/hosts
172.17.0.2  c51a702ba714
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.18.0.3  test2
172.18.0.3  test2.testnet

Note that in the /etc/hosts file there are 2 entries for test2, one is the network name that was created earlier.

Containers cannot communicate if they are not on the same network, even if you know the ip address of the container

~ > docker run -it --name test3 alpine sh
/ # ping test2
ping: bad address 'test2'
/ # ping test2.testnet
ping: bad address 'test2.testnet'
/ # ping -c 1 -W 1 172.18.0.3
PING 172.18.0.3 (172.18.0.3): 56 data bytes

--- 172.18.0.3 ping statistics ---
1 packets transmitted, 0 packets received, 100% packet loss