Spring Cloud Netflix Eureka
Eureka know the every instance of port and serve as main router
Request -> Api gatewaty -> Eureka -> microservices
Axon Framework and axon server
Choreography
Orchestration
CQRS => Command Query Responsibility Segregatoin
Eureka Discover server will know eureka discovery client automatically which instance was running
api gateway sit as main router, validation, logging, specific filter, it have buid in load balancer
stop at D:\Video\Spring Boot Microservices, CQRS, SAGA, Axon Framework[TutsNode.com] - Spring Boot Microservices, CQRS, SAGA, Axon Framework\5. Spring Cloud API Gateway & Load Balancing
serve.port =0 => random port number
Download Axon server
D:\Video\Spring Boot Microservices, CQRS, SAGA, Axon Framework[TutsNode.com] - Spring Boot Microservices, CQRS, SAGA, Axon Framework\6. Axon Server - Getting Started
Axon config file https://docs.axoniq.io/reference-guide/axon-server/administration/admin-configuration/configuration
-p publish 8124 port number on left side is local machine :8124 port no. on right side is docker container
-v path to local storage :/data path to the folder(storage) in docker container
docker will find docker repository
docker run --name axonserver -p 8024:8024 -p 8124:8124 -v "D:\projects\MircoServices\docker-data\data":/data -v "D:\projects\MircoServices\docker-data\eventdata":/eventdata -v "D:\projects\MircoServices\docker-data\config":/config axoniq/axonserver
docker ps -a
docker stop containerId docker rm containerId
Create Command Pattern Verb + Noun + Command
Client App <=Command/Reply> Command Bus <=> Command Handler <=> Domain <=Events> Repository <=Events> Event Store
Product Aggregate will hold the current state of product object
Aggregate class is core of microservices, It is domain object hold the current state of main object
Aggregate product will be dispatch it will be method in aggregate class
every time one state of product info change event sourcing method will be invoked
when product update command received state of this prodcut aggregate object will first need to be loaded from event store action framework will first create new empty object of product aggregate that is why it need empty constructor it will read every single event that is stored in event store for this aggregate and it will apply event to aggregate
In aggregate class => second handler will be used as command handler method and it will be invoked when create product command is dispatched
Noun + Performed Action + Event
event handler are used to update aggregate state called event source in handling method
@AggregateIdentifier in productaggregate associate dispatch @TargetAggregateIdentifier in createProductCommand
D:\Video\Spring Boot Microservices, CQRS, SAGA, Axon Framework[TutsNode.com] - Spring Boot Microservices, CQRS, SAGA, Axon Framework\7. CQRS Pattern. Products Microservice 13. @EventSourcingHandler need to read again
If we are using axon with spring cloud => maven start demanding google guava to be added in dependencies
to test on tomorrow => ProductController response = commandGateway.sendAndWait(createProductCommand); set break point and running as debug mode
ProductAggregate set break point for throw exception and aggregateLifecycle.apply
Productcontroller => pom.xml => add spring boot data jpa starter dependencies add h2 or mysql up to you
D:\AA Backup\Video\Spring Boot Microservices, CQRS, SAGA, Axon Framework[TutsNode.com] - Spring Boot Microservices, CQRS, SAGA, Axon Framework\7. CQRS Pattern. Products Microservice
V + N + Command CreateProductCommand
N + PerformedAction + Event ProductCreatedEvent
D:\AA Backup\Video\Spring Boot Microservices, CQRS, SAGA, Axon Framework[TutsNode.com] - Spring Boot Microservices, CQRS, SAGA, Axon Framework\8. CQRS. Persisting Event in the Products database
Stop at here 6-May-2022 D:\AA Backup\Video\Spring Boot Microservices, CQRS, SAGA, Axon Framework[TutsNode.com] - Spring Boot Microservices, CQRS, SAGA, Axon Framework\9. CQRS. Querying Data
1st start axon server 2nd edureka discovery 3rd product service 4th Api Gateway
Core package share between query and command api
Query class start with Find+XXX+Query
Request => Java Bean => Java Bean Validation => Controller => Command Gateway --> Dispatch => Command Bus <= Command Handler --> Dispatch => Event Bus <= Event Handler
Command Handler validation =>
Message dispatch interceptor => when a command is dispatched on command bus => intercept between Command gatewaty and command bus => can do additional logging, validation
Stop at here 12-June-2022 D:\AA Backup\Video\Spring Boot Microservices, CQRS, SAGA, Axon Framework[TutsNode.com] - Spring Boot Microservices, CQRS, SAGA, Axon Framework\12. Validation. Message Dispatch Interceptor
interceptor need to register in spring config
if added interceptor in interceptor throw exception it will not go to commandhandler Aggregate class
Stop at here 6-July-2022 D:\AA Backup\Video\Spring Boot Microservices, CQRS, SAGA, Axon Framework[TutsNode.com] - Spring Boot Microservices, CQRS, SAGA, Axon Framework\13. Validation. How to check if record exists Set based Constitency validation
how to check if product is existing product when creating new product client api first assist an event in event store and only after the event is persisted and it will publish an event to synchronized data between the event store and query the database communication bet command and query api is done via event messaging
sync bet two models might take sometimes because of event messaging
command api quickly check if record already exists before persisted in event store
Solution to this problem is Axon framework set based constituency validation
Command model can contain any form of data model, introduce a small lookup table which contain productId and title when the prouct create, command api will first lookup in lookup table lookup table should not contain exact same product as in database lookup table only store product fields that are need to look up table and see if exists (eg. id and title)
how to query look up table before command handler process command
message dispatcher will intercept the command before it is processed by command handler method if exist in lookup table then command will be blocked
Creating product lookup table should be in separate datbase for testing purpose it can be in same databaase
@ProcessingGroup("product-group") in event Handler axon will create separate tracking event processor, use special tracking token same event and different thread and node
14 July-2022 stop at here D:\AA Backup\Video\Spring Boot Microservices, CQRS, SAGA, Axon Framework[TutsNode.com] - Spring Boot Microservices, CQRS, SAGA, Axon Framework\14. Handle Error & Rollback Transaction
When exceptions are thrown in event, default behavior is to look for an error msg and continue the execution coz code and command handler was successfully executed => app will recieved a successful response
If an exception is thrown and was not handled in event handler method -> it will not prevent all event handlers from execution But execution will continue and the code in other method in same process and group will continue
exception msg will be thrown in event handler method will also not be handled by try catch in controller class or in centralized controller advice exception handler class.
If you want exception msg to propagate all the way to a controller method or to a controller advice class need to write additional code to configure the event processor to propagate the exception so you can catch in differenct place To do that we will use listener invocation class handler provied by axon framework If doing this execution in other event handler method handle an error in controller class and return a custom error msg txn will roll back For this to work => need to configure our event and method to be in same processing group that is configured to use subscribing event processor. Event processor is component that is incharge of managing technical aspect of providing the event handler
Event processor have 2 forms Tracking event procesor Pull their msg from a source using a thread it managed itself. A different thread Will retry processing the event using incremental back-off period processor will go into error mode, will release the token and retry an event as an incremental interval starting at one second will double after each attempt and to a maximum wait time of 60 seconds per attempt is achieved this back-off time ensures that if another node is able to process event successfully, it will have opportunity to claim the token requried to process the event
Subscribing event processor Subscribing themselves to source of events and are invoked by thread managed by publishing mechanism. Same Thread By default exception raised by event handlers are locked and processing will continue next event will report the publication error to the component that provided an event will have an exception bubbled up to the publishing component of event allowing to deal with it accordingly
If we propagate the exception all the way up, we can make entire txn will roll back we will use subscribing event processor to manage event handler in product event handler class
17 july 2022 stop D:\AA Backup\Video\Spring Boot Microservices, CQRS, SAGA, Axon Framework[TutsNode.com] - Spring Boot Microservices, CQRS, SAGA, Axon Framework\14. Handle Error & Rollback Transaction\6. Trying to handle the @CommandExecutionException
import org.axonframework.messaging.interceptors.ExceptionHandler;
handle exception that are thrown from event handling functions in the same class
To do rollback and undo db changes made by event handler method if processing group is configured to use subscribing event processor when using try catch event processor boz event handler method is use subscribing event processor , these events are processed in same thread and processing events in same thread gives this posibility to roll back the whole txn. if exception happen default behavior is to handle exception and continue execution.
one way is to use create own exception that catch exception thrown in event and methods Create events exceptio handler and implement Listener invocation of axon (ListenerInvocationErrorHandler) this will be last rethrow to make txn roll back (propagating error handler)
register listerinvocation
25 july 2022 D:\AA Backup\Video\Spring Boot Microservices, CQRS, SAGA, Axon Framework[TutsNode.com] - Spring Boot Microservices, CQRS, SAGA, Axon Framework\14. Handle Error & Rollback Transaction
- Trying how transaction rollback works
2-Aug-2022 D:\AA Backup\Video\Spring Boot Microservices, CQRS, SAGA, Axon Framework[TutsNode.com] - Spring Boot Microservices, CQRS, SAGA, Axon Framework\15. Assignment. Orders Microservice