I have 2 option.
1)when addItemTobasket request come. gRPC request to product, pricing, user service and get informations . and save them to cart db.
Or not fetch other service information. Save only references like id. And save basket db. When get basket request call gRPC request aggragate all service datas as viewmodel and return that.
2) create shared redis session server and when addeditem to cart event raise itemAddedToCart includes reference ids. And main services consume that event. Product service get product with id that come with event and write Product info shared redis. pricing service price etc. When getbasket request come data is ready in redis.
For 1) it coupled all servies. it is not good for ddd.
For 2) it is async. When user add item to cart. Waits a responsr success or failed.
If there is better best practice please share with Me.
Honestly I'd say just go with option 1. It's not as complex as there aren't so many interconnected parts. Also depending on the size of your app, that kind of coupling is easy to remove later on when you gain a better understanding of what is going on.
Related
I have product service, category service, promotions service, search service.
When User want to add product. CreateProductRequest come to product service. Request includes product data and datas of other services like categoryId,uncalculated price , too. After product is added. I need to send other servie datas. Category service needs productId and CategoryId. Promotions service needs productId and price.
After creat eproduct transaction commited;
1) I put all data in ProductCreatedEvent that includes saved productId, categoryId, uncalculated price etc. Every service get what it needs from event and save to own db. I publish event with RabbitMQ
2) Send via seperated commands to services.I send commands with RabbitMQ
And What If there is no category that id come with event and Category services didn't save. But Product saved at product Services ?
or what do you suggest ?
To answer the question, it's important to keep in mind the difference between a command and event. A command is a request to do something. An event is a record of something that has happened. One key difference is that a command can be rejected.
When looking at your use case, publishing events to other services makes the most sense. The product has been created and you are notifying the other bounded contexts that care about the change. If you issue a command, you are telling other bounded context to make a change that may or may not fail.
That said, you each bounded context may receive the event and produce a command within their own context to update aggregates managed within. As such, the difference is subtle between these two:
- Issue a command to each bounded context
- Issue an event to each bounded context and they can then trigger a command as needed
But given the above, the notification of the creation of the product should not fail. It has happened already. From there, each context can decide what to do about it.
I have a question about the integration events used in a microservice / CQRS architecture.
The payload of the event can only have references to aggregates or can it have more information?
If only reference ids can be sent, the only viable solution is to bring the rest of the information with some type of call but the origin would have to implement an endpoint and the services would end up more coupled.
ex. when a user is created and the event is raised.
UserCreated {
userId
name
lastname
document
...
}
Is this correct?
If only reference ids can be sent,
Why would only that be allowed? I have worked with a system which was using micro-services, CQRS and DDD(similar like yours) and we did not have such restrictions. Like in most cases it is: "What works best for your application/business domain". Do not follow any rule blindly. This is perfectly fine to put other information in the events Payload as well.
the only viable solution is to bring the rest of the information with
some type of call but the origin would have to implement an endpoint
and the services would end up more coupled.
This is fine in some cases as well but this brings you to the situation to have additional call's after the event has been processed. I would not do this unless you have a really heavy model/models and it would affect your performance. For example if you have an event executed and based on userId you would need to load a collection of related objects/models for some reason. I had one similar case where I had to load a collection of other objects based on some action on user like event UserCreated. Of course in this case you don't want to send all that data in one Event payload. Instead you send only the id of the user and later call a Get api from the other service to get and save that data to your micro-service.
UserCreated
{
userId
name
lastname
document
... }
Is this correct?
Yes this is fine :)
What you could do instead:
Depending of your business scenario you could publish the information with multiple events with Stages and in different States.
Lets say from UI you have some Wizard-like screen with multiple steps of creation. You could publish
event: UserCreatedDraft with some initial data from 1st Wizard page
event: UserPersonalDataCreated with only part of the object related to private data
event: UserPaymentDataCreated with only the payment data created
UserCreatedFinal with the last step
Of this is just an example for some specific scenario which depends on your use case and your Business requirements. This is just to give you an Idea what you could do in some cases.
Summary:
As you can see there are multiple ways how you can work with these kind of systems. Keep in mind that following the rules is good but in some cases you need to do what is the best based on your business scenario and what works for some application might not be the best solution for your. Do what is most efficient for your system. Working with micro-services we need to deal with latency and async operations anyways so saving some performance on other parts of the system is always good.
I'm building a e-commerce with DDD and Event Sourcing, CQRS. My ideia is separate each AR in a microservice.
In my AR ShoppingCart I need a VO Item with productId and a Price, because price doesn't change after add to the cart.
I have another AR Product that control the price.
My problem is, how get the Price from AR Product without a synchronous request to the Product since I'm using a event architecture?
Fundamentally, what you are trying to do is copy information from one aggregate root to the other.
There are two approaches you might take.
One is to think in terms of a cache - we pass to the shopping cart an instance of a domain service that knows how to take a correlation id (product code?) and get a cached copy of a price. So we have a background process that copies pricing information from the pricing micro service to the shopping cart micro service, and then the autonomous shopping cart relies on its locally cached copy of the price.
Important note: there's nothing wrong with including timeliness metadata in the cache, so that the sharping cart can include intelligence about whether or not the cached information is "too old".
The other is more direct - have a method by which you can send a command with the price to the shopping cart, and build some orchestration logic that observes which shopping carts need prices, then send send a command to the cart with the appropriate price.
If you have two microservices, you can have each microservice publish a stream of events. Your ShoppingCart microservice can consume PriceChanged events from your Product microservice and maintain a local cache of the last price per Product. When you add a Product to a ShoppingCart, you would reference the local cache of prices.
This same approach of listening to events as a means of communication scales up from inter-Aggregate to inter-BoundedContext or inter-Microservice and even inter-System. Depending on your sensitivity to price changes, you might have to employ other approaches as described, but I assume you have some tolerance to eventual consistency given your choice in the CQRS+ES pattern.
I'm having a problem understanding how basic communication between microservices should be made and I haven't been able to find a good solution or standard way to do this in the other questions. Let's use this basic example.
I have an invoice service that return invoices, every invoice will contain information(ids) about the user and the products. If I have a view in which I need to render the invoices for a specific user, I just make a simple request.
let url = "http://my-domain.com/api/v2/invoices"
let params = {userId:1}
request(url,params,(e,r)=>{
const results = r // An array of 1000 invoices for the user 1
});
Now, for this specific view I will need to make another request to get all the details for each product on each invoice.
results.map((invoice)=>{
invoice.items.map((itemId)=>{
const url=`http://my-domain.com/api/v2/products/${itemId}`
request(url,(e,r)=>{
const product = r
//Do something else.....
});
});
});
I know the code example is not perfect but you can see that this will generate a huge number of requests(at least 1000) to the product service and just for 1 user, now imagine if I have 1000 users making this kind of requests.
What is the right way to get the information off all the products without having to make this number of requests in order to avoid performance issues?.
I found some workarounds for this kind of scenarios such as:
Create an API endpoint that accepts a list of IDs in order to make a single request.
Duplicate the information from the Product service within the invoice service and find a way to keep them in sync.
In a microservices architecture are these the right ways to deal with this kind of issues? For me, they look like simple workarounds.
Edit #1: Based on Remus Rusanu response.
As per Remus recommendation, I decided to isolate my services and describe them a little bit better.
As shown in the image above the microservices are now isolated(in specific the Billing-service) and they now are the owners of the data. By using this structure I ensure that Billing-service is able to work even if there are async jobs or even if the other two services are down.
If I need to create a new invoice, I can call the other two microservices(Users, Inventory) synchronously and then update the data on the "cache" tables(Users, Inventory) in my billing service.
Is it also good to assume these "cache" tables are read-only? I assume they are since only the user/inventory services should be able to modify this information to preserve isolation and authority over the information.
You need to isolate the services as so they do not share state/data. The design in your question is a single macroservice split into 3 correlated storage silos. Case in point, you cannot interpret a result form the 'Invoicing' service w/o correlating the data with the 'Products' response(s).
Isolated microservices mean they own their data and they can operate independently. An invoice is complete as returned from the 'Invoices' service. It contains the product names, the customer name, every information on the invoice. All the data came from its own storage. A separate microservice could be 'Inventory', that operates all the product inventories, current stock etc. It would also have its own data, in its own storage. A 'product' can exist in both storage mediums, and there once was logical link between them (when the invoice was created), but the link is severed now. The 'Inventory' microservice can change its products (eg. remove one, add new SKUs etc) w/o affecting the existing Invoices (this is not only a microservice isolation requirement, is also a basic accounting requirement). I'm not going to enter here into details of what is a product 'identity' in real life.
If you find yourself asking questions like you're asking it likely means you do not have microservices. You should think at your microservice boundaries while considering what happens if you replace all communication with async queued based requests (a response can come 6 days later): If the semantics break, the boundary is probably wrong. If the semantics hold, is the right track.
It all depends on the resilience requirements that you have. Do you want your microservice to function when the other microservices are down or not?
The first solution that you presented is the less resilient: if any of the Users or Products microservices goes down, the Invoice microservice would also go down. Is this what you want? On the other hand, this architecture is the simplest. A variation of this architecture is to let the client make the join requests; this leads to a chatty conversation but it has the advantage that the client could replace the missing information with default information when the other microservices are down.
The second solution offers the biggest possible resilience but it's more complex. Having an event-driven architecture helps a lot in this case. In this architecture the microservices act as swimming lanes. A failure in one of the microservices does not propagate to other microservices.
I am working on a personal project where I want to automate the TA assignment system. I want to use Node and MongoDB for this. Though I have some idea about MongoDB, I am new to NodeJS. The aim of the projest is to do something like this :
A school administrator submits the course for which he/she wants to hire a TA.
The database is already populated with eligible students(more than two). The fields assoc with each student is [Student ID, Seniorty(sophomore,junior,senior),Course Taken or not, grade,presentStatus(Avlbl/Hired)]
At any point of time, the school admin requests a TA for a course, he gets the most senior eligible student available in the db.
Once the student is assigned, his status is changed to Hired.
I was planning to implement this using a queue. (Storing all the available students in that course in a queue and assigning the TA-ship to the senior student available in the front of the queue). As soon as he/she is assigned a TA, they are removed from the queue and pushed back into the db with the PresentStatus as 'Hired'. The problem I am facing is, I am not able to understand how I should be implementing the functionalities of the queue using NodeJS. During my research about the approach, I found something related to monq and a blog as well where they have discussed implementing it with Kue(backed by Redis instead), however I am still not able to visualize how this idea should be implemented using queues in NodeJS. Any help would be appreciated.
RabbitMQ is an option you are looking for.
You have to create a message sender and message consumer. The consumer will have a corresponding queue. Once the queue is filled with a message, the consumer will grab it and do it's process. In your scenario, it checks the student's status and then change him/her as hired in your database. What your sender does is that it packages a student's information and put it in the consumer's queue. I can imagine what will be happening in your case: a student submits request on his/her side. The node.js api receive it and pack information. Then it sends it to your customer queue. Your customer will process it if it's free. If it's busy, the information will be waiting in the queue. I recommend you to use json for students' information when different components have to communicate.
Here is the official website of RabbitMQ: https://www.rabbitmq.com/getstarted.html
Hope it helps.