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Docker

Container Networking

Each container connect to a private virtual network → NAT firewall (of host)

All containers on a virtual network can talk to each other (without -p)

Best practice is to create new virtual network for each app cluster

“my_web_app” for php/apache and mysql

“my_api” for mongo and nodejs

You can:

make new virtual network

attach container to more than 1 virtual network

skip virtual and use host IP ( --net=host )

use different Docket network tools, drivers to gain new abilities

Networking Commands

# default host:container ports

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

# check ports

docker container port webhost

# check ip of a container

docker container inspect --format '{{ .NetworkSettings.IPAddress }}' webhost

# container is not in the same network with host

ifconfig en0

How network packet move in and out

⁠

Networking commands

# list all docker network

docker network ls

# will return 3 default network & drivers

bridge # (default docker network, routed through NAT)

host # use host as default network

none # no networking for container

# check how many containers connect to bridge network

docker network inspect

# check IPAM (subnet x.x.x.x/16 of all available IP)

# check containers (id and name and IP of each container)

# create a new nerwork

network create my_app_net # it use default driver like 'bridge'

--driver

# attach a container to new network

docker network connect webhost1 my_app_net

docker container run -d --name webhost2 --network my_app_net nginx

# 2 containers run same my_app_net network

DNS

use DNS to inter-com between containers

# run ping inside webhost1 to ping to webhost 2

docker container exec -it webhost ping webhost2

# create a default network named 'roundrobin'

docker network create roundrobin

# create 2 containers, both DNS named 'search', connect to roundrobin, from image 'elasticsearch' (it will have different id and names)

docker container run -d --net roundrobin --net-alias search elasticsearch

# run a container from image 'aline', remove when exit

# run on 'roundrobin' network

# execute shell: nslookup on that container, look for 'search' DNS

docker container run --rm --net roundrobin alpine nslookup search

# if you keep pinging that 'search' DNS, it will randomly use 2 containers

docker container run --rm --net roundrobin centos curl -s search:9200

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