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The last couple of videos we've had have been just a bunch of lecturing for me.

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I know that's super boring.

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Just one more lecture and we're gonna start writing some code again in this video we're going to go

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over the design of the event bus.

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We're going to talk about how we can use the event bus to communicate events for one service over to

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another as a reminder.

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We're going to try to build as much of as this stuff as possible from scratch rather than using some

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off the shelf solution.

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And that includes the event bus.

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So we're going to build this event bus on our own.

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We're going to build it using JavaScript and express.

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I want to give you a couple notes on how this thing needs to work.

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OK so event buses the first thing to understand about them is that there are many different implementations

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available.

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You might have heard of terms like rabbit and Q Kafka or nets.

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These are all different types of event buses.

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They're open source projects.

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You can download them and run them yourself or you can get some kind of pre hosted provided solution.

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The one common thing between these different event buses is that they're going to receive events and

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then publish them out to listeners when we use the term events here.

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We're really talking about some piece of information.

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There's no set structure of what a event has to look like.

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It can be Jason.

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It can be Rob bytes of data.

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It can be a string.

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It can be whatever you want to share between your different services.

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When we use the term listeners we're talking about other services that want to listen to events that

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are being emitted now between these different implementations of say rabbit and Q Kafka Nats and many

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others that exist out there.

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Turns out that there are many very small features available in these different event buses that make

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some things a lot easier or a lot harder.

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So in this larger application that we're gonna work on in the second half of this course I picked a

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event bus that is really easy to get started with extremely fast.

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But there are some downsides to it as well somethings that are going to make our lives a little bit

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more complicated.

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So you just need to be aware that you cannot just pick one these implementations off the shelf you kind

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of have to evaluate them and understand what they can really do for you.

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Now once again we are going to build our own event buses Inn Express.

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It is not going to implement the vast vast majority of features that a normal event bus has to.

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Ours is going to be incredibly simplistic incredibly simple not very useful outside this one single

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implementation.

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But again we're going to build this from scratch just you have a really good idea of what is going on

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behind the scenes.

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And yes again for our next application we're going to work on the much larger one.

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We are going to use a production grade even bus.

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This is an event bus that is used in many many very large deployments and projects.

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So you're going to get some very practical experience with some real technology as well.

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All right.

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Let's talk about the Express based event bus that you and I are going to put together.

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Now this really is a very simplistic implementation for event bus.

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The reason we are doing such a simple implementation is just you can see how this stuff kind of works

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behind the scenes.

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And so you can very easily see the flow of data throughout our application.

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Let me tell you about how this thing is going to work we are going to add in a new route to our postal

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service intercom in service.

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We're also gonna make sure that our query service has a very similar route as well.

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Each of these routes are going to watch for a post request to a path of slash events.

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We'll talk about the purpose of that in just a moment.

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At some point time inside our application we're going to have our postal service or common service decide

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that it needs to emit an event whenever a service needs to emit any event it's going to make a post

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request off to this new event bus that you and I are going to put together again this event bus right

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here is going to be a plane express application.

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Essentially we're really just doing a post request from one service to another in that post request.

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We're going to attach along some event data so it's going to be some object that represents this event

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right here this event bus is going to receive this event that's going to take that event and make a

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series of post request with it.

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So it's going to take all that event data and it's going to take that exact information and just send

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it off to a post request to local host 4000 slash events.

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That would be our postal service.

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That's going to make an identical request off to a local Post four thousand one slash events.

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And same thing or local localized 4000 to social events.

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So in all three of these post requests it's going to send along this event data so in short any time

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one of our services makes a post request over to event bus event bus is just going to take that exact

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information and throw it out to everything else that we have running inside our application even the

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same service that emitted the event originally so that's it.

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That's how simple our event bus is going to be.

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Now again as we start to use some more production ready application or solutions here for the event

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bus you can see that there's a lot more to this implementation.

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But at the end of the day this is pretty much what is going on more or less we're throwing an event

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over to the event bus even bus is just going to echo that event back over to all of our different services

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now that we've got an idea of what's going on here.

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Quick pause.

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We're going to start building this event bus which is a very simple very straightforward in the next

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video.