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[Intro Music]

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I have just demonstrated to you how

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you're able to use variables when

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you need to insert for example, path

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in the 'docker run' command. And

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notice that if you use variables,

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then it is important in which

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folder you are located, if you use

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specifically 'PWD' variable, because

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it will actually get path to

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current folder and place it inside

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of the 'docker run' command. Great.

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Now let me explain you actually

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what happens when you run container,

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and how you're able to run

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container in background using '-d'

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option. Okay, let's get started

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with hello-world container, and

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let's run it once again, 'docker run

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hello-world', Enter, you will see

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this result in terminal but

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container exits. And I have

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explained you before that basically

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container exits as soon as there

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are no processes running inside of

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the container. And in this example,

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there was process that has printed

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this text to this terminal, and

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afterwards this process was

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terminated. And Docker terminates

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container afterwards as well. Let's

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try to run another container, for

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example, alpine. Let's clear

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terminal, and 'docker run alpine'.

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Same happens here. Docker runs

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container, it creates process, but

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this process terminates, and

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afterwards Docker terminates

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container as well. But which

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process actually starts in this

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specific container? Let me enter

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'docker history alpine', and here at

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the top you will see command, 'CMD /bin/

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sh', in this case, I'll explain you

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what this command actually means a

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bit later. But now you should

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understand and remember that with

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this command, you are able to find

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at the top specific command that is

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executed as soon as a new container

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is created based on specific image,

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in this case the image name is

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'alpine'. So, if you create a new

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container with 'alpine' image, it

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runs command '/bin/sh'. It is actually a

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shell. But this process, this process

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has standard in, 'stdin' and standard

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output, 'stdout'; and it waits that someone

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or some other process will connect

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to each standard in and standard

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output. And in such case, this

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process will be kept running, and

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will accept the some characters

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via standard input, and may produce

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some output via standard output, 'stdout'.

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But if we simply run container

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in such way, we don't connect to

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standard input of this process, and

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that's why this process terminates

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automatically, because there is no

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standard input connection or

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standard out connection. That's

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what happens under the hood. But

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you are able to connect to standard

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input of this process if you add

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two flags, '-i' and '-t'.

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Basically you could add only '-i' flag,

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let me show you that. 'docker

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run -i alpine', and now I am

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connected to standard in of this

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process '/bin/sh', and if I enter for

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example, 'ls', I will see a list of

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folders inside of the container.

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And if I go to another tab and

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enter 'docker ps', I will see a list

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of containers that are currently up

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and running. And again I see here

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same command as I have shown you

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just in 'docker history' output, it is

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command that was automatically

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executed when a container was

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created. And for this specific

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image, alpine image, this command is

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'/bin/sh'. But let me now try to exit

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from this connection to standard

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input of 'sh' shell inside of the

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container. As usually let's try to

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use Ctrl+C combination, and you see

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it doesn't work. The reason for

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that is that we are connected now

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directly to specific 'sh' process, and

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it does not accept such termination commands.

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You are also able to try to stop

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container here using 'stop' command,

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like 'docker stop', and here maybe

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either ID of the container or its

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name, for example this one. Let me

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copy the name, paste here, press

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Enter, and you'll see that Docker is

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trying to stop container. Let's

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wait a bit. It actually sends SIGTERM

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signal to 'process'. But in

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such case, 'sh' is running with

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process id 1, and it doesn't

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accept any such kind of commands.

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And when Docker is not able to stop

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container during 10 seconds, it

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will try to kill it, it has

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actually hard stopped the

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container, and in such case with

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'stop' command, it will try to

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perform, let's say, soft stop. So

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finally, in such case in 10

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seconds, Docker has stopped this

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container. And of course here in

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this step, we have disconnected

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from standard input of the 'sh'.

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Great. This is what happens when you

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try to connect to specific process

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that actually keeps container

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running. But as soon as process

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ends, container exits as well. Let's

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try something else. Let's clear

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terminal here, and let's try to run

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nginx server, 'docker run nginx',

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and here you see that we are

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actually connected to standard

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input of nginx process. We could

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verify that here. Let's go back to

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this step, clear it, and 'docker ps',

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and we see that nginx container is

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running. And here you see basically

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command that was executed. And here

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was actually name of process that

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is running inside of the container.

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This process name is nginx. And

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actually here on this step, we are

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able to get the output from this

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process. And actually in previous

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lectures, we have seen that it

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produces some logs when clients

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connect to this container.

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Actually, let me show you that quickly.

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Let me terminate this container.

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Actually here, I'm able to use Ctrl+

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C, and let's use port mapping. 'docker

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run -p 8080:', here will be '80

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nginx'. Press Enter, and let's

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now try to connect to port 80, and

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connection was successful, and here

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nginx has set up default content.

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Let's go back to this output, and

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here we see actually some text that

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was produced into standard output

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by nginx process inside of the

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container, here is this process.

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Great. But how you're able actually

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to run container in background? You

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are able to use '-d' option. And

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in such case, those logs will be

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actually created and saved in

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background into log file, and you will

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be able to observe them later on.

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But with '-d' option you

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will get back to terminal because

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container will be running in background.

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Let me show you that. Let me

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terminate this one, clear terminal,

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and here run same container, but

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with option '-d' without any

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arguments, '-d', and you'll

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simply see ID of the container that

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was just created. We could verify

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that here in this step 'docker ps'.

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You see here, start characters

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of this ID, and you see that now

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this container is still running

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because there was running process,

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nginx process, but we cannot

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connect it to that process here.

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That's what actually this '-d'

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option does. With this option in

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place, container is started in

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background, and you will get back to

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your terminal window, but container

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will be still kept running in

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background. Let me try now to

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connect to our web page here,

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refresh page, go back here, and of

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course in this window I will not

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see any logs, because again

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container was running in

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background. But you are able to

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read those logs using 'docker logs'

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command, and use some characters

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from the ID of specific container

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that is up and running now. And I

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could use for example characters

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'92', that are starting

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characters of this ID here, and

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let's press Enter, and you see a

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log that tells us that there was

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connection to web server, and here

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was a response code, 'Not Modified'.

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That's how you're able to get logs

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that were produced by a specific

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process inside of the container.

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And again, this container, nginx

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container is still up and running

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here because there was a single

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process inside of that container.

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Now you are able if you want to

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stop this container using 'docker

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stop' command. Let me clear terminal,

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again 'docker ps', and get some

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characters from ID or use this name,

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and use 'docker stop' command, and

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type here for example '92', and

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now you see that this container was

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stopped much faster than

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previous container, because

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previously that container was not

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listening to any commands, and

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that's why finally in 10 seconds

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process was killed automatically.

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In such case this process, nginx

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process listens to such commands,

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and Docker was able to terminate

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this container in soft, let's say

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manner. That's what '-d'

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option does, and that's how you're

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able to run such containers as for

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example, nginx in background, it

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will not interrupt your current

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terminal window, and you will be

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able to perform any other actions,

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create other containers, and so on.

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Great. That's all for this lecture.

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And in the next one let me

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demonstrate you how you're able to

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run multiple containers

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simultaneously using same image.

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Let's do the next. Bye-Bye.

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[Outro Music]

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[no audio]

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[Clock Ticking]

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[no audio]