Docker: How a docker container communicate to another docker container in the same/different host ?

Question

There are multiple cases:
1. A number of containers have been launched in the same host. how these container communicate to each other
2. Out of "x" numbers of containers in the same host, I want to enable communication between two specific containers. How I can achieve this ?
3. Containers have been launched into different hosts machine and I want to enable communication between these containers. What are the options available ?

Answer 1

Let's say we have two containers on the same host, run these commands

Create a network:

docker network create -d bridge "your-created-network" // Your network, you can name anything
docker run -d -p 8080:80 --network="your-created-network" --name=nginxone nginx:alpine

and change the nginx port to 8081 to up another container of nginx

docker run -d -p 8081:80 --network="your-created-network" --name=nginxtwo nginx:alpine

to communicate between these two containers you need to execute:

docker exec -it nginxtwo sh
ping nginxone  // this will work

if you want to communicate between two specific containers, add your created network to those containers.
For the second case, I haven't tried but you can use boot2docker or apache.