If you want to be able to ping or basically access a running docker container from another container by simply using the docker name rather than an IP address, DNS must work well. Docker natively provides DNS capability to get containers in the same network to communicate between containers over their DNS names as IP addressing changes as containers go in and out.

Basics of Docker Networking;

Docker Network Defaults;
Each container connected to a private virtual network “bridge”
Each virtual network routes through NAT firewall on host IP
All containers on a virtual network can talk to each other without -p

Docker Network Best Practices;
Create a new virtual network for each app:

Step 1:
Let us begin by creating two containers; I am using the NGINX Image.

You can download the nginx to the Local Cache.

$>docker image ls 
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
httpd               latest              417af7dc28bc        7 days ago          138MB
nginx               latest              7e4d58f0e5f3        12 days ago         133MB
mysql               latest              e1d7dc9731da        13 days ago         544MB
alpine              latest              a24bb4013296        3 months ago        5.57MB

Get the image by typing “docker container pull nginx”

docker container run -d --name container1  -p 8080:80 nginx
docker container run -d --name container2  -p 8088:80 nginx

Let us verify

$docker container ps
CONTAINER ID        IMAGE               COMMAND                  CREATED              STATUS              PORTS                  NAMES
a1147ca12e97        nginx               "/docker-entrypoint.…"   1 hours ago          Up 10 minutes       0.0.0.0:8080->80/tcp   container1
0e364de8f313        nginx               "/docker-entrypoint.…"   1 hours ago          Up 10 minutes       0.0.0.0:8088->80/tcp   container2

Important note: it is of utmost importance to explicitly specify a name with –name for your containers. The reason being that it will not work with the auto-generated names that Docker assigns to your container(s).

Step 2:
Create a new network:

docker network create nginx-network

Verify if this network is listed in the docker networks

C:\>docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
25d4ec1592eb        bridge              bridge              local
ba0017e88f28        host                host                local
06658aee8f0c        nginx-network       bridge              local
70be58caf984        none                null                local
33668dd3b17f        webservices         bridge              local

Step 3:
Connect your containers to the network:

docker network connect nginx-network container1
docker network connect nginx-network container2

Step 4:
Verify if your containers are part of the newly created network (nginx-network):

docker network inspect nginx-network

  "ConfigOnly": false,
        "Containers": {
            "0e364de8f3134e242e513a6cf3da4b69bb38fb7ef17213a309a7bda27b423b3a": {
                "Name": "container1",
                "EndpointID": "fdf973b2840adea185bec76c8684bb1c404a21ccb9947c16c58119b350aebb36",
                "MacAddress": "02:42:ac:12:00:03",
                "IPv4Address": "172.18.0.3/16",
                "IPv6Address": ""
            },
            "a1147ca12e97cb054af40ab67255d9dd5817d7197695e3756ee5fd614195de77": {
                "Name": "container2",
                "EndpointID": "6edb537acdc3b1ec6ee233993d9e6d28cd8a62055600300d0e77e48c94ee9a88",
                "MacAddress": "02:42:ac:12:00:02",
                "IPv4Address": "172.18.0.2/16",
                "IPv6Address": ""
            }

Install ping for nginx as not all images come prepackaged with the ping utility

Run docker container1 and install ping. you can do so by going to the bash of the container by typing;

These two commands are needed. You can go ahead line by line as per below or in one single line as per the instruction 2 below;

Instruction 1:

 
apt-get update
apt-get install iputils-ping

Instruction 2:

$docker container exec -it container1 bash
root@a1147ca12e97:/#
root@a1147ca12e97:/# apt-get update && apt-get install iputils-ping

Repeat above step for container2

Final Step:
Finally test the connection between container1 and container2.

$docker container exec -it container1 ping container2
PING container2 (172.18.0.3) 56(84) bytes of data.
64 bytes from container2.nginx-network (172.18.0.3): icmp_seq=1 ttl=64 time=0.050 ms
64 bytes from container2.nginx-network (172.18.0.3): icmp_seq=2 ttl=64 time=0.043 ms
64 bytes from container2.nginx-network (172.18.0.3): icmp_seq=3 ttl=64 time=0.142 ms
64 bytes from container2.nginx-network (172.18.0.3): icmp_seq=4 ttl=64 time=0.145 ms
64 bytes from container2.nginx-network (172.18.0.3): icmp_seq=5 ttl=64 time=0.142 ms
64 bytes from container2.nginx-network (172.18.0.3): icmp_seq=6 ttl=64 time=0.066 ms
64 bytes from container2.nginx-network (172.18.0.3): icmp_seq=7 ttl=64 time=0.047 ms
^C
--- container2 ping statistics ---
7 packets transmitted, 7 received, 0% packet loss, time 129ms
rtt min/avg/max/mdev = 0.043/0.090/0.145/0.047 ms

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