WEBVTT

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-: In the last section,

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we spoke about how Docker Compose automatically

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sets up some networking between these different services,

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or these different types of containers that we define

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inside of our Docker composed file.

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Now that all this stuff is supposedly set up,

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let's figure out how to start up Docker Compose

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using this file.

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All right, so remember, the entire purpose,

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or, well, I should say one of the purposes

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of Docker Compose is to kind of make it easier

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to run all the different commands that you usually run

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with docker run.

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So whereas before, we would start up a new instance

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of a container using docker run,

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and then the name of the image that we wanted

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to create the container out of

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to create a instance of all the containers,

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or all the images or all the services

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listed inside of our composed file.

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We're going to run the command docker-compose up.

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Now, that one's pretty straightforward.

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So essentially, instead of saying run, we're gonna say up.

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And we don't have to specify an image.

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We're not specifying an image,

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because Docker Compose is going to look

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into our current working directory,

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and automatically look for a docker-compose file

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inside there.

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Now, the thing to be aware of

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is that before, we had the two separate Docker commands

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to build an image and run it,

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so if we wanted to rebuild the image from our Dockerfile,

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and then start an instance of it, two separate commands.

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But in the Docker Composed world,

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if we ever want to rebuild the images that are listed inside

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of our Docker composed file,

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for example, if we wanted to have Docker Compose

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rebuild this container right here,

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or the image used for that container,

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we write docker compose up --build.

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And so this --build right here is what essentially

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tells Docker Compose, "Start up our containers again,

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but make sure you try to rebuild them ahead

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of time so that we get all the latest changes."

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Okay, so let's give this a shot.

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I'm gonna flip on over to my terminal.

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I'm inside of my project directory,

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and I can definitely verify

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that I have my docker-compose file inside of here.

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So I'm going to run docker-compose up.

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Now, I want you to take a look

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at the very first line right here.

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The very first line says,

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"Creating network visits_default."

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So like I said before, when you just create a new set

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of containers or services with Docker Compose,

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it's going to automatically make a network for you

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that's going to join those different containers together.

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After that, we can see that it is creating an image

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for our Node application.

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And then if we scroll down a little bit more,

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we're gonna see a whole bunch of different output down here.

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The most important lines to see are,

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"Creating visits Node app one."

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So that's a single instance of our node-app service.

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And then we've got a single instance

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of our Redis Server as well.

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After that, we'll then start to see all the output

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from both of those different services start to appear.

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So every line here that's appearing in yellow for me

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is output from the Redis Server.

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And if I scroll down a little bit more,

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I'll eventually see some output from the Node application.

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So it looks like based on ready

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to accept connections right here,

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and listing a Port 8,081 right here,

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definitely looks like both of our containers

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set up were created successfully.

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So let's open up our browser.

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We're gonna try to open up our Node application,

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and see if the entire app works.

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All right, so I'm gonna open up Local Host 4,001.

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Remember, we made that kind of last minute change there.

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We had hard coded to say Port 8,081,

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but at the last minute we decided to change the port used

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to 4,001.

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So make sure you're go into Local Host, 4,001.

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And then sure enough, we see number of visits as zero,

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and then we can refresh.

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And every time that we refresh the page,

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we'll see that number of visits start to increment.

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Awesome.

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So that's a basic usage of Docker Compose.

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We created two separate services,

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and Docker Compose automatically made connections

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between the two available.

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The real key thing to keep in mind here

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is that in order to communicate between the two,

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we used a host name of the name of that other service,

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or that other container that was created,

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and that name is specified inside

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of our Docker composed file right here.

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So anytime you are making use

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of maybe some database driver

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inside of your web application layer,

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anywhere you would normally put in a connection URL,

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or connection URI,

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you can instead just list the name of that other container,

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and the host name will be automatically resolved

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for you by Docker.

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All right, now, quick break.

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There is still one or two quick things

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I want to go over on Docker Compose,

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so I'll see you in just a minute.