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In this video, we are going to learn a lot of the best practices and event driven architectures.

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So we will follow the design principles and the best practices when developing our lambda based, event

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driven serverless applications.

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Lambda is very good fit when we are working with the event driven architectures because the nature of

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the Lambda executions trigger from events.

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Events can come lots of resources and able to trigger lambda functions.

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So lambda is a complete service that runs custom function code and return response to the events.

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Most services generate events for communicating each other, and most of the services are event sources

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for a lambda.

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LAMDA always handle all interactions with the Lambda API and there is no direct invocation of functions

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from outside to the service.

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We can see the image on the slide Lambda Handle event with the Lambda API.

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The main purpose of lambda function is to handle events when a function is triggered by an event.

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This is called an invocation.

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Lambda function are limited to 15 minutes in duration, but on average most of the calls take less than

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a second across all the customers in some compute incentive operations.

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It may take several minutes to process a single event, but in most cases, the time is short.

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And even triggering a lambda function could be almost anything.

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You can see the image on the slide from the rest API.

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A HTTP request with Amazon API Gateway as scheduled task managed by the Amazon Event Breach Cloud Watch

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Logs Rule or an Amazon S3 notification like object uploaded into the bucket.

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Even the simplest lambda based application used at least one event.

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So that's why we said lambda is very good fit for the event driven architectures because the fuel of

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the lambda is immense.

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So the event is a JSON object that contains all information about what happened.

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Events are represents a change in the system state they are immutable.

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You can see the example event json to trigger a lambda function in the image of the slide.

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The first parameter of every lambda handed function contains the event JSON object so you can find the

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example event JSON object that triggered the lambda function and you can see the function image that

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takes event parameter into lambda handle method.

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So at that stage, the event parameter is very important when developing our lambda function.

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If you look at the Lambda Handle method, you will see that the first parameter is event into lambda

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handle method.

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So with using this event JSON object, we can access the event parameters into lambda function.

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For example, let's look at this slide image we have.

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We have a naive order event triggers to lambda function.

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So if I would like to get the order that details attribute value into lambda function, basically I

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can take the information with the event that source or event that detail into my Lambda 100 function

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because lambda triggered this event json object with passing parameters in the handle method.

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So an event could be custom generated from other microservices such as the Neve or the generated in

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an e-commerce application.

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We will have exactly the same use case into our serverless e-commerce application.

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The event also can be generated from the existing sources like Amazon in case when a new message is

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available in the queue, it can go to Lambda with pulling queue records from the Amazon queue.

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So even event architectures rely on the creating event into all the application state chains that are

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observable by other services.

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But the event publisher system is unaware of which consumers are subscribing that event.

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We call that there are loosely coupled services.

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Most lambda based applications use a combination of services for different requirements about storage,

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API management and integrating with the other systems and services.

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In these applications, Lambda is a connecting between services, providing the business logic to transform

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data that moves between the services.

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So now we can talk about design principles and the best practices by developing LAMDA based, event

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driven applications.

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So we set that solar applications mostly using a combination of services that integrated with the custom

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code run in the Lambda functions.

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So we can think we can find the most integrated services which using advanced lambda functions, you

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can see the image on the slide.

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These services are mostly commonly using in service application with a lambda function.

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You can see the category and also the services.

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We will also use these services into our service hands on projects.

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Also, there are some design patterns in distributed architectures that we will follow when we implement

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applications using the ADA services.

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ADA Services has already implement some of the distributed architecture design patterns that we can

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use easily without investing time to develop these patterns from scratch.

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When your application is using these patterns, we can basically use corresponding services.

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That is the table in the slide.

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So here you can see the patterns and here you can see the available services that we can use for that

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patterns.

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These services and patterns are designed to integrate with ADA Lambda functions, and we can also use

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infrastructure as code to create and destroy resources in the ADA services.

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We can use any of these services with using ADA SDK without needing to install applications or configure

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servers.

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So these are the best practices when designing well-designed serverless applications that we will follow

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when developing our services.

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Hands on labs.

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As a summary in serverless word, Lambda is core services for building any event based architectures.

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That means we will also follow these lambda design principles and the best practices when developing

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our Lambda Base event driven serverless applications.

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Basically, we will group these events as a bounded context in order to develop boundaries of our microservices

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in the service applications.

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That means we will develop lambda function as a microservices into our event driven microservice architectures

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in the service hands on labs.