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So friends, now that we understand how to deal with facts as well as how to set

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variables utilizing

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the register keyword, now what I want to talk to you about is how we can

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utilize handlers within

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our playbook. So with that said, let's just get to it. So let's go to the

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answerable documentation

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and find out what these handlers actually do for us. So quite simply just

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search for

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answerable handlers if we click this top link right here scrolling on down we

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can see here

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immediately handlers allow us to run operations on a change. So really what we

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're thinking about
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're thinking about

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here is conditional logic once again. So this time imagine that we only want to

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run a particular

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task depending on the result of the previous task. The example they gave here

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is let's imagine you

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make some type of configuration change to a particular service and for that

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change to actually take

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an effect. What we would have to do would be to restart the service now we don

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't just want to

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restart the service if the configuration changes did not actually make any

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difference. So we don't

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just want to automatically restart the service. We want to push a configuration
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just want to automatically restart the service. We want to push a configuration

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and if the

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configuration happens to make a change to the system then and only then would

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we like to have

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a task to restart that service. Now notice here it says handlers are tasks that

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are only run when

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notified this concept here really is important notification. This is how we

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actually inform

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the handler to run. So let me go and give you a simple example then okay. Now

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the first thing I

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want to do is I want to ensure that I have engine X running on both of my
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want to do is I want to ensure that I have engine X running on both of my

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managed devices. Now you'll

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notice if I say for example log into the yellow box and I just do a system CTL

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status on engine X

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notice I actually don't have engine X on this device the same is true of my

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blue box. So what

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I will do quickly is I will just run an answerable playbook to install engine X

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on both of my devices

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right now. So let's create play six dot y amount and we're going to insert mode

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have my three

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high friends get the playbook a name which is called this playbook six because
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high friends get the playbook a name which is called this playbook six because

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I have no creativity

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we're going to target the all group I will just say gather facts I specify my

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tasks and the task

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here it's just going to be called install engine X and because I'm on red hat I

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'm going to use the

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built in DNF module and the package I want to install is engine X and I want

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the state to be

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present and just before I do anything what I will do is I'll just say gather

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facts is the value

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false so let's save this and run the playbook. So as we can see here the change
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false so let's save this and run the playbook. So as we can see here the change

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has been made we

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should now have engine X on both of our devices. Now here is the thing if I

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happen to go to my

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devices right here if I do system cta status on engine X we can see here I now

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have engine X but

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as it stands right now it is inactive so what I'm going to do here actually and

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I probably should

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have done this within the playbook but nevertheless let's just do this manually

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start the server is

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typing my password now it should be running which indeed it is and let's just

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do the same thing

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on the blue box or do pseudo system cta start engine X. If I browse to local
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on the blue box or do pseudo system cta start engine X. If I browse to local

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host we can see

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here we have the content of my engine X webserver. So here's what I want to do

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I want to actually

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make a change to the actual HTML file that has been pulled in by engine X and

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when I make that

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configuration change for that to actually operate what I'm going to do is I

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want to restart my

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server now I'm going to restart it only if a change happens to be detected that

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means we're

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going to use a handler. So let me create a new playbook called play seven dot y
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going to use a handler. So let me create a new playbook called play seven dot y

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ml let's just do

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the usual have a three hyphens gather playbook a name which is called this

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playbook seven testing

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handlers what we're targeting we're targeting all our set gather facts to false

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and now define my

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tasks and I'll just say copy HTML file to device so what I'll do is I'll use

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the answer will build

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10 template module and for a source I'm going to specify a file within my

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templates directory and

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it's just going to be called index dot j2 okay and the destination this time it

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's going to be user
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's going to be user

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share engine X html and then the file will be index dot html this is a common

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and well-known

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path the engine X uses to consume its index file now the interesting part here

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is this part we're

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going to say notify this is how we notify our handler so pretty much I can give

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any name I so

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wish here we just want to make sure it syncs up with whatever we call the

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handler so I could say

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restart engine X upon change okay and now I'm going to do it at the same level

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of indentation as my
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of indentation as my

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tasks I want to actually define my handlers now similar I'm going to give a

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name now this is the

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interesting part this here is what we're going to sync up with okay so I named

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the actual notification

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restart engine X upon change that is going to be the same one I use right here

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so restart engine

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X upon change and now I specify what it is I want to do so I'm going to say my

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service is engine X

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and I'm going to specify that the state should be restarted so basically when I
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and I'm going to specify that the state should be restarted so basically when I

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copy over this

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particular file to this particular destination on both of my devices if I'm

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able to text that this

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particular file has changed we want to notify this particular handler and this

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particular handler

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is this one right here and what is the action we're going to perform we're

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going to target the

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engine X service and we're going to restart it again it will only happen if a

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change is detected

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right here so what I'm going to have to do is I'm going to have to create this

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templates index.j2

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file right here inside of my templates directory I'm going to have a file
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file right here inside of my templates directory I'm going to have a file

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called index.j2 and this

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here is the simple template I'm going to use basically I'm going to make the

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change welcome to

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John's engine X server now what I will do here within the actual scale I'll

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actually give you a

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copy of this particular template so you can just modify as needed okay so let

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me just save this

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right here now one thing I want to show you right now see if I go back to my

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engine X server on

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say for example this device we just full screen this temporarily if I just

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arrow up and check the

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status notice this server has been running for six minutes okay now when I run
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status notice this server has been running for six minutes okay now when I run

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this playbook

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this is going to restart and the clock will restart as well so I'll say answer

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my playbook

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place 7.yml and to answer so now be copy over the changes and it will detect

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that we have a change

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and therefore the handler takes effect and as we can see the handler has indeed

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made a change we

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have restarted the engine X server so if I go back to my yellow box and I just

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arrow up and run the

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command once again look at this right here the server has only been running for
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command once again look at this right here the server has only been running for

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23 seconds it was

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indeed restarted now the cool thing is if I actually go to my browser here

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check this out right here

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the engine X server now has these new changes welcome to john's engine X server

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now the cool

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thing is if I go back to my playbook and I rerun it and copy the same

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configuration file over again

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look at the actual output because there was no change the same file is already

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on the system

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because of that the handler didn't actually execute therefore we didn't
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because of that the handler didn't actually execute therefore we didn't

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actually restart the server

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unnecessarily so once again if I go back to my terminal on this particular

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device arrow up

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we can see here the server is still running it wasn't actually restarted the

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clock didn't go

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back to zero again now one thing I just want to point out with respect to the

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notification

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notice the way we had to sync up this particular name with this particular name

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here now the reality

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is we don't actually have to do that we can also utilize the lesson directive

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so what that will

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allow me to do it will allow me to mismatch the name of the handler and still
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allow me to do it will allow me to mismatch the name of the handler and still

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also execute let

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me show you what I mean so right now if I just happened to mismatch this say

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for example and

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let me go into the templates I'm going to index.j2 and we'll make an actual

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change here let's just say

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blast or a change is actually made save here the change will be made but the

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handler is not going

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to be called because the mismatch okay so run this notice this we have an error

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the handler was not

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found okay so check this out in here now as opposed to having to match these up
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found okay so check this out in here now as opposed to having to match these up

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what I will do here

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instead let's just give this a shorter name like let's just say engine x

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handler okay now what I

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will do here is I will use the lesson directive and I will match that up with

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the notified directive

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so notice this matches exactly this but what it does it frees us up to give the

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task a rather long

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and descriptive name so this task could be called restart engine x server when

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a config has changed

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so as opposed to having to copy this long descriptive sentence right here
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so as opposed to having to copy this long descriptive sentence right here

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instead we can just use

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shorthand by making use of the lesson directive so we'll go back into the

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templates once again

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change this back maybe add in some exclamation marks so that there is a new

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change right at the

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changes go back and now we'll run the playbook and because you have a change we

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're now going to call

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the handler once again and indeed the change has taken effect so if we go back

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to our devices

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let's go to our server and we'll refresh and check this out we now have the

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changes with the three ex

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Commission marks.