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[Intro Music]

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Our goal at the moment is to

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establish communication between two

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containers. And we will start

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simple and I'll explain you how

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you're able to ping one container

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from another in default bridge

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network. And for that, we will

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create two busybox containers.

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At the moment there was a 'wordpress'

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container running and it is

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completely safe to stop it and

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remove at the moment. But no

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worries, we will get back to

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'wordpress' container a bit later.

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All right, let me stop this

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container 'docker stop 75',

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[no audio]

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and let's prune all stopped containers

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'docker container prune'. Yes. And all

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containers were removed. Wonderful.

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Let's now create two busybox

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containers. Here in this step will

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be first one and in another tab we

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will create second one. Great.

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Let's use 'docker run' command. Recap

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that 'busybox' image is already

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in our local cache. 'docker run',

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I'll use two options '-it'; and

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here will be 'busybox', like so. And

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in another tab let's also start

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one more 'busybox' container 'docker

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run -it busybox'. Great. We have

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logged into 'sh' shell here in this

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container, and in this container. And

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now let's verify which IP addresses

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were assigned to those containers.

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For that you could use command

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'hostname -i'; and here let's

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enter this command as well,

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'hostname -i', and you see that

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the IP addresses that were assigned

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to those containers are different.

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Here you see that this address ends

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with 2, and here this address

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ends with 3. But you may notice

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that those IP addresses are from

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the same sub-network. It is

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basically Private Sub-network

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called 172.17.0.0 with subnet

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mask 16. And those IP addresses

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from this range are used for

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assignment to containers by

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default, it is actually default

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network. And let's now verify

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whether those containers are able

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to communicate between each other

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or not. And for that, we will

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simply use ping utility that will

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perform a connection test from one

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IP address to another. And from

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this 'busybox' container, we could ping

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another IP address of another

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container using ping utility. This

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utility is available in 'busybox'

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container out of the box. Let's use

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it, 'ping 172.17.0.3', and you see

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that we get response from another

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container. And that means that

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there is connection between two

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containers and they are able to

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communicate over any TCP or UDP

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ports, because this ping utility

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works on the third level of the OSI

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model, and it means that all levels

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up will work as well. No worries,

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we'll get back to network concepts

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a bit later in the course, and I'll

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explain you all of that in details.

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For now you need to understand that

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those containers are able to

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communicate over any TCP or UDP

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ports. Wonderful. Also, you're able

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to verify connection from this

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container, and here you're able to

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use the same command 'ping

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172.17.0.2, and you of course will

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get response from this 'busybox'

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container. Great. That's how IP

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addresses are assigned by default

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containers and how you're able to

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communicate between containers by

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default in default bridge network.

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Also you are able to verify which

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IP address was assigned to specific

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container by using the command

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'docker inspect'.

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Let me open up a new tab here, and

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first let's enter 'docker ps', and

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you'll see two containers running.

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Here is the first ID and here is the second

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ID. And now let's use 'docker inspect'

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command, 'docker inspect', and pass

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here ID of any of the containers.

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Let's use this ID. Let me copy it,

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paste here. And you'll see IP

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address almost at the end of this

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output. Here is the IP address

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assigned to this 'busybox' container.

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And if you'll verify the details

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about another container, let me do

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so, 'docker ps', 'docker inspect', and

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let's use ID this one, copy it,

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paste here, you'll see another IP

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address assigned to this container.

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You may also notice that there was

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Gateway setting and it is equal for

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both containers. It is actually

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virtual IP address located at the

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Docker Host, and it acts as a

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default gateway for all containers

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that are running in default bridge

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network. Wonderful. These aer

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fundamentals of IP networking, by

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default in Docker. Again, here was

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default network 172.17.0.0, and

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subnet mask is 16. Here you see

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'IPPrefixLen' as third line

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here in this output. And that means

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that you may see IP addresses like

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172.17.5.6, or 100.7, or like in this

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case 172.17.0.2, 5, 10, and so on. But

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this part will be the same for all

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IP addresses, it is prefix. All

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right, that's the basics of IP

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networking between containers that

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are created in Docker by default.

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Also let me demonstrate to you that you

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are able to connect to any IP

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address or hostname in internet

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from container. And for that you

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could use same command ping and for

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example, type 'ping google.com', and

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you'll get response from Google,

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you will get response actually from

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IP address of one of the Google's

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servers. Great. That's all what I

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wanted to show you here in this

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lecture. And the most important

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outcome is that containers by

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default may communicate between

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each other using IP addresses.

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Wonderful. Let's now proceed and

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next let's try to create mysql

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container, and see whether we will

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be able to start it without any

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options or not. I'll see you next. Bye-Bye.

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[no audio]