docker networks

concepts for private and public comms in containers

review of docker container run -p
for local dev/testing, networks usually "just work"
quick port check with docker container port <container>
learn concepts of docker networking
understand how network packets move around docker
each container uses a priv virt net "bridge"
each virt net routes through nat firewall
all containers on a virt net can talk without -p
"batteries included, but removable"
- defaults work well in many cases, but easy to swap out parts to customise it
make new virt nets
attach containers to more than one virt net
skip virt nets and use host (--net=host)
use different docker network drivers to gain new abilities

docker container run -p 80:80 --name webhost -d nginx
docker container port webhost

--format - a common option for formatting the output of commands using 'go templates'
```
docker container inspect --format '{{ .NetworkSettings.IPAddress }}' webhost
```

command	description
`docker network ls`	show networks
`docker network inspect`	inspect a network
`docker network create --driver`	create a network
`docker network connect`	attach a network to a container
`docker network disconnect`	detach a network from a container

docker network create <network_name>

docker container run -d --name <container_name> --network <network_name> <image>

using connect and disconnect you can add more networks or change networks, like plugging additional nics or switching eth cables.

understand how dns is the key (can't rely on ips)
- can't use ip addresses because so dynamic
see how it works by default with custom networks
learn how to use --link to enable dns on default bridge network
containers on the same network have automatically dns resolution with container name
default bridge network does not have dns by default
- can use --link when starting containers to link in default bridge network