DNS services
By default, a container inherits the DNS settings of the host, as defined in the /etc/resolv.conf configuration file. Containers that use the default bridge network get a copy of this file, whereas containers that use a custom network use Docker’s embedded DNS server, which forwards external DNS lookups to the DNS servers configured on the host.
➤ DNS stands for Domain Name System.
➤ DNS is how domain names are translated into IP addresses. DNS is what allows you to use your web browser to find web sites.
➤ DNS makes it possible for us to use easy to remember domain names in place of complex IP addresses.
➤ Containers uses DNS to communicate.
➤ Containers don’t use IP address to Communicate.
docker network create -d bridge mynetwork
The -d flag tells Docker to use the bridge driver for the new network. You could have left this flag off as bridge is the default value for this flag. Go ahead and list the networks on your machine:
$ docker network ls
NETWORK ID NAME DRIVER
bb9dc0e96308 bridge bridge local
2435e354c788 host host local
b451a848eecb mynetwork bridge local
987819fa19d0 none null local
Then Inspect the network
docker network inspect mynetwork
[
{
"Name": "mynetwork",
"Id": "d2c2870a549606fdc8aa47c6d06e6d2358bebcd3806f5428b33d3fa69abc5cad",
"Created": "2022-02-26T22:03:13.255007777Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": {},
"Config": [
{
"Subnet": "172.19.0.0/16",
"Gateway": "172.19.0.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {},
"Options": {},
"Labels": {}
}
]
Let's create two containers to run on mynetwork
root@dockerboss:~# docker run -d --name my_nginx1 --network mynetwork nginx:alpine
start another container with my_nginx2
root@dockerboss:~# docker run -d --name my_nginx2 --network mynetwork nginx:alpine
Then let us see all the containers that are running with docker ps -a
root@dockerboss:~# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
971e6c87abe7 nginx:alpine "/docker-entrypoint.…" About a minute ago Up About a minute 80/tcp my_nginx2
02f9f07eb7d7 nginx:alpine "/docker-entrypoint.…" 3 minutes ago Up 3 minutes 80/tcp my_nginx1
8872e2ec486f nginx "/docker-entrypoint.…" 14 minutes ago Up 14 minutes 0.0.0.0:8080->80/tcp, :::8080->80/tcp affectionate_blackburn
Then let us inspect the network again with docker network inspect mynetwork
root@dockerboss:~# docker network inspect mynetwork [ { "Name": "mynetwork", "Id": "d2c2870a549606fdc8aa47c6d06e6d2358bebcd3806f5428b33d3fa69abc5cad", "Created": "2022-02-26T22:03:13.255007777Z", "Scope": "local", "Driver": "bridge", "EnableIPv6": false, "IPAM": { "Driver": "default", "Options": {}, "Config": [ { "Subnet": "172.19.0.0/16", "Gateway": "172.19.0.1" } ] }, "Internal": false, "Attachable": false, "Ingress": false, "ConfigFrom": { "Network": "" }, "ConfigOnly": false, "Containers": { "02f9f07eb7d73f9aef7a206f1f8a159319f1194dd26131145a3ba9b21fa9b248": { "Name": "my_nginx1", "EndpointID": "67dea7f43119a77a82344b68bace369a12f350b7b859408841d169a487d45a80", "MacAddress": "02:42:ac:13:00:02", "IPv4Address": "172.19.0.2/16", "IPv6Address": "" }, "971e6c87abe7d4c54ade03941e60b6889509eb670580e04e96c82adfc8eb7fd2": { "Name": "my_nginx2", "EndpointID": "7236d22c29151425bc1ba9aa546adc39155073a21b7e692b82ab97695f398077", "MacAddress": "02:42:ac:13:00:03", "IPv4Address": "172.19.0.3/16", "IPv6Address": "" } }, "Options": {}, "Labels": {} } ] root@dockerboss:~#
Then let's try to ping my_nginx1 from my_nginx2
root@dockerboss:~# docker exec -it my_nginx1 ping my_nginx2
PING my_nginx2 (172.19.0.3): 56 data bytes
64 bytes from 172.19.0.3: seq=0 ttl=64 time=0.103 ms
64 bytes from 172.19.0.3: seq=1 ttl=64 time=0.086 ms
64 bytes from 172.19.0.3: seq=2 ttl=64 time=0.083 ms
64 bytes from 172.19.0.3: seq=3 ttl=64 time=0.085 ms
64 bytes from 172.19.0.3: seq=4 ttl=64 time=0.084 ms
64 bytes from 172.19.0.3: seq=5 ttl=64 time=0.086 ms
64 bytes from 172.19.0.3: seq=6 ttl=64 time=0.084 ms
64 bytes from 172.19.0.3: seq=7 ttl=64 time=0.088 ms
64 bytes from 172.19.0.3: seq=8 ttl=64 time=0.083 ms
64 bytes from 172.19.0.3: seq=9 ttl=64 time=0.087 ms
64 bytes from 172.19.0.3: seq=10 ttl=64 time=0.097 ms
64 bytes from 172.19.0.3: seq=11 ttl=64 time=0.086 ms
^C
--- my_nginx2 ping statistics ---
12 packets transmitted, 12 packets received, 0% packet loss
round-trip min/avg/max = 0.083/0.087/0.103 ms
Then why we do not use ip address because it is not static and when you stop this container and re-start it again, the chance that same container may not have same ip address to connect
so let us stop my_network1 which has 172.19.0.2
so let us stop my_network1 which has 172.19.0.2
root@dockerboss:~# docker stop my_nginx1
Then start a new container my_nginx3 on same network mynetwork
root@dockerboss:~# docker run -d --name my_nginx3 --network mynetwork nginx:alpine
so let us inspect the network to see the ip address that was assign to my_nginx3
root@dockerboss:~# docker network inspect mynetwork [ { "Name": "mynetwork", "Id": "d2c2870a549606fdc8aa47c6d06e6d2358bebcd3806f5428b33d3fa69abc5cad", "Created": "2022-02-26T22:03:13.255007777Z", "Scope": "local", "Driver": "bridge", "EnableIPv6": false, "IPAM": { "Driver": "default", "Options": {}, "Config": [ { "Subnet": "172.19.0.0/16", "Gateway": "172.19.0.1" } ] }, "Internal": false, "Attachable": false, "Ingress": false, "ConfigFrom": { "Network": "" }, "ConfigOnly": false, "Containers": { "971e6c87abe7d4c54ade03941e60b6889509eb670580e04e96c82adfc8eb7fd2": { "Name": "my_nginx2", "EndpointID": "7236d22c29151425bc1ba9aa546adc39155073a21b7e692b82ab97695f398077", "MacAddress": "02:42:ac:13:00:03", "IPv4Address": "172.19.0.3/16", "IPv6Address": "" }, "f38c47ea5a38ff350f3d3221c0bffdddf1be549e9f1ad3a6ab70a7155f72a3cc": { "Name": "my_nginx3", "EndpointID": "13af56e584d08f0f0ec6e4f75776ac68be75f032c3e873312bab28b8a7c582f2", "MacAddress": "02:42:ac:13:00:02", "IPv4Address": "172.19.0.2/16", "IPv6Address": "" } }, "Options": {}, "Labels": {} } ]
That is true to see that my_nginx3 container was assigned the ip address that my_nginx1 was work assigned earlier
Let start my_nginx1 with docker start my_nginx1
and inspect the network again to see the new ip address for my_nginx1
[ { "Name": "mynetwork", "Id": "d2c2870a549606fdc8aa47c6d06e6d2358bebcd3806f5428b33d3fa69abc5cad", "Created": "2022-02-26T22:03:13.255007777Z", "Scope": "local", "Driver": "bridge", "EnableIPv6": false, "IPAM": { "Driver": "default", "Options": {}, "Config": [ { "Subnet": "172.19.0.0/16", "Gateway": "172.19.0.1" } ] }, "Internal": false, "Attachable": false, "Ingress": false, "ConfigFrom": { "Network": "" }, "ConfigOnly": false, "Containers": { "02f9f07eb7d73f9aef7a206f1f8a159319f1194dd26131145a3ba9b21fa9b248": { "Name": "my_nginx1", "EndpointID": "e58148da92df9f9576e2badb04f83067b67b224e4ba04d8b243ed6b60dcc2b97", "MacAddress": "02:42:ac:13:00:04", "IPv4Address": "172.19.0.4/16", "IPv6Address": "" }, "971e6c87abe7d4c54ade03941e60b6889509eb670580e04e96c82adfc8eb7fd2": { "Name": "my_nginx2", "EndpointID": "7236d22c29151425bc1ba9aa546adc39155073a21b7e692b82ab97695f398077", "MacAddress": "02:42:ac:13:00:03", "IPv4Address": "172.19.0.3/16", "IPv6Address": "" }, "f38c47ea5a38ff350f3d3221c0bffdddf1be549e9f1ad3a6ab70a7155f72a3cc": { "Name": "my_nginx3", "EndpointID": "13af56e584d08f0f0ec6e4f75776ac68be75f032c3e873312bab28b8a7c582f2", "MacAddress": "02:42:ac:13:00:02", "IPv4Address": "172.19.0.2/16", "IPv6Address": "" } }, "Options": {}, "Labels": {} } ]
To resolve this problem , docker uses container dns instead of container ip
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