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- [Alana] We walked you
through the core components

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of AWS CodeDeploy in a previous video,

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but it's time to get a bit
deeper into one of them,

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the AppSpec file.

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It's important to have a good
understanding of this file,

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as CodeDeploy relies on it heavily.

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This AppSpec is a YAML or JSON file

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that contains locations for
all the installation files,

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scripts, and when to
initiate specific actions.

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This is where you get to control

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how your revision deployments
are actually managed,

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and how you determine a
deployment was successful.

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Let's take a look at the AppSpec file

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that we'll be using later in the labs.

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Note that this is an AppSpec file

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that's used for Amazon
EC2 based deployments.

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If you're looking for more information

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on serverless AppSpec files,

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check out the reading
following this video.

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All right, so this AppSpec
file is a YAML file,

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and it's pretty simplistic in nature.

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A lot of AppSpec files can
get pretty complicated,

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but I'll talk you through all your options

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and why we chose the ones we
did for this specific file.

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So, this file is broken
out into four sections:

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version, os, files, and hooks.

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We could additionally have another section

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called the permissions section,

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which we'll talk about a bit later.

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Out of all the sections,

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the version and the os
are the simplest parts.

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The version refers to the
CodeDeploy AppSpec version,

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and not the version

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of your specific
application or deployments.

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And currently, the only
accepted value is 0.0.

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The os section, as you
may have already guessed,

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stands for operating system,

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and it only accepts two possible
values, Linux or Windows.

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The EC2 instance you'll
be working with in the lab

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is a Linux box, so we chose Linux.

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Now, all the rest of the
sections are optional.

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That means the hooks, files,
and the permissions sections

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are not required.

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So let's talk about why.

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The files section is only necessary,

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if you're going to be copying
files to your instance

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during the deployments.

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It has a source and
destination subsection.

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The source subsection
identifies a file or directory

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from your revision to copy.

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The destination identifies
the location on this instance

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of where the file or
directory should be copied.

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So for our AppSpec file,
we want the index.html file

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to be copied to the

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var/www/html directory on our instance.

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The next section we are going to review

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is the hooks section.

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The hooks direct the CodeDeploy agent

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as to what it needs to
do and in what sequence.

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Some of the main hooks that
you can use are BeforeInstall,

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AfterInstall, ApplicationStart,
ApplicationStop,

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and ValidateService.

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Each of these is used to
run scripts that you specify

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when the hook is initiated.

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You'll notice that each of these hooks

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is structured the same way.

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You specify the location of the script,

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the timeout you want
to allow for it to run,

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and if you're running a Linux deployment,

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runas refers to the level

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at which you want to run the script.

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Or, in other words, the
user on your Linux instance

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you want to use to run
the script, such as root.

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Note that we're not using
every one of these hooks.

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In our file, we're only
using three of these hooks,

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BeforeInstall, ApplicationStop,
and ApplicationStart.

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That's because they're
the only ones necessary

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for this deployment, so
we've completely omitted

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the other options from the file.

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Let's talk about each of
these hooks in detail.

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The Before and AfterInstall
hooks are used for the script

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that you need to run before
the installation happens,

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and after the installation is complete.

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For example, here, we're
linking to a script

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that installs the dependencies

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needed to run our application.

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If I look at the script,

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you can see that I'm installing
an Apache web server here,

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which is needed for the site.

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Going back to the AppSpec file,

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the ApplicationStop and
ApplicationStart hooks

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are used to run any scripts needed to stop

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and start the application.

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We're using these hooks to start
and stop our Apache server.

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So, looking at the start_server
script in a text editor,

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you can see we're doing just
that, starting the server.

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And in this stop_server script,

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you can see that I'm checking

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to see if the Apache
web server is running,

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and if it is, I stop it.

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Now, there is another
hook that you cannot use

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to initiate a script,
and it's called Install.

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In CodeDeploy, the Install
stage is just the stage

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where it copies over the
files from the source

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to the destination on your behalf.

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Lastly, you can use the
ValidateService hook

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to run any scripts that
you will use to test

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and make sure that
everything has been installed

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and started correctly.

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After the hooks, that leaves
us with one last section,

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the permissions section.

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I'll go ahead and paste in

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a permissions section to this file,

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so that you can see some of the settings.

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The permissions section is only valid

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if the os setting is set to Linux.

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It refers to the permissions
you want to apply

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to the files being copied
in the file section.

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If you're specifying permissions,

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then the file section is required.

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I won't go through every
part of the permissions,

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but I do want to state that
if you use permissions,

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the one required part within permissions

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that you must include
is the object section.

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Object refers to the set
of system files, folders,

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or directories that the
specified permissions

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are applied to after
the file system objects

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are copied to the instance.

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There's a lot more to the AppSpec file

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that I can cover in this video,

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so make sure to check
out the notes section

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for more information and resources.

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I'll also provide examples

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of how you can use the permissions section

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for your deployments.