running commands within a Docker user defined network - docker

Question

After creating the next network using docker:
sudo docker network create --driver bridge mynet_nw
how can I do to issue commands from inside this network? i.e it is like simulating my machine is inside mynet_nw so I can issue ping commands to different docker images created inside mynet_nw?
Thx

Answer 1

You issue commands from any Docker container inside your network. You just need to add a container first. See docker network connect for that.
Either way, any Docker container on a network can talk to any other Docker container on the same network. Assuming you have your host, containerA, and containerB, you'll be able to ping any of those three from each other:
containerA:~$ ping 172.18.0.1 # from containerA to host
56 bytes from 172.18.0.1: icmp_seq=0 ttl=64 time=0.101 ms
56 bytes from 172.18.0.1: icmp_seq=0 ttl=64 time=0.098 ms
56 bytes from 172.18.0.1: icmp_seq=0 ttl=64 time=0.102 ms
56 bytes from 172.18.0.1: icmp_seq=0 ttl=64 time=0.100 ms
containerA:~$ ping 172.18.0.3 # from containerA to containerB
56 bytes from 172.18.0.3: icmp_seq=0 ttl=64 time=0.082 ms
56 bytes from 172.18.0.3: icmp_seq=0 ttl=64 time=0.079 ms
56 bytes from 172.18.0.3: icmp_seq=0 ttl=64 time=0.116 ms
56 bytes from 172.18.0.3: icmp_seq=0 ttl=64 time=0.094 ms
Asssuming you know hostnames, you should be able to even ping with hostnames directly. This might be a bit weirder when attempting to ping your host, but it should work between containers.
containerA:~$ ping containerB # from containerA to containerB
56 bytes from 172.18.0.3: icmp_seq=0 ttl=64 time=0.067 ms
56 bytes from 172.18.0.3: icmp_seq=0 ttl=64 time=0.084 ms
56 bytes from 172.18.0.3: icmp_seq=0 ttl=64 time=0.080 ms
56 bytes from 172.18.0.3: icmp_seq=0 ttl=64 time=0.0811 ms

Answer 2

Generally I suggest to read the documentation for the docker network commands: https://docs.docker.com/engine/reference/commandline/network_connect/#related-commands
https://docs.docker.com/engine/userguide/networking/work-with-networks/
Anyway the docker network generates a network and you need a container to execute commands in there.
Example:
docker run -it alpine --network mynet_nw /bin/bash
ping mydb
You can alway check the network from the host itself if you know the name of the container:
INSTANCE_NAME='myalpine'
IPADD=$( docker inspect --format='{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' $INSTANCE_NAME )
ping $IPADD