In this video of code decode we have explained saga design pattern in Spring boot microservices.
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Why SAGA ??
We know that Design pattern gives solutions to common problems faced by us “THE DEVELOPERS”. So What problem is solved by this SAGA design pattern ?
The problem started as soon as we moved from Monolithic application to Microservice Architecture.
We will take example of Swiggy , zomato.
You
Choose your dishes,
Add them to Cart and checkout
Make Payment
Order gets Delivered
Our order is marked as completed after delivery is successful.
In monolithic it’s not a problem as we have 1 database , multiple Tables like Orders, Payments, Delivery Etc. Now in 1 Single Atomic transaction we can do all these steps and if payment fails, everything gets rolled back.
Now we moved to microservices architecture and Segregated the whole zomato or swiggy application to
Order service
Payment service
Delivery Service
Now your order service accepts your order, Payment service validates the payment done and Delivery service is responsible for delivery of your order to your home. When delivered successfully the orders is marked completed in the application. This is happy case.
Ever thought about the worst case Delivery is failed as no delivery partner was available. Your payment was done, Money got deducted and now No food. At Least we need to get the money back and Order must be marked as cancelled.
For this to happen we need a Transaction rollback . Transaction did get rolled back but only the scope of transaction was in Delivery service. The boundary for this transaction ended in Delivery service.
Ways to Implement SAGA?
There are two type of saga implementation ways
choreography
orchestration
What is Choreography Saga Pattern?
Choreography is a way to coordinate sagas where participants exchange events without a centralized point of control
With choreography, each microservices run its own local transaction and publishes events to message broker system and that trigger local transactions in other microservices.
Advantages of Choreography Saga Pattern?
Good for simple workflows that require few participants and don't need a coordination logic
Doesn't require additional service implementation and maintenance.
Doesn't introduce a single point of failure, since the responsibilities are distributed across the saga participants.
Disadvantages of Choreography Saga Design Pattern?
Workflow can become confusing when adding new steps, as it's difficult to track which saga participants listen to which commands.
There's a risk of cyclic dependency between saga participants because they have to consume each other's commands
What is Orchestration Saga Pattern?
Orchestration is a way to coordinate sagas where a centralized controller tells the saga participants what local transactions to execute.
The saga orchestrator handles all the transactions and tells the participants which operation to perform based on events.
Advantages of Orchestration Saga Pattern?
Good for complex workflows involving many participants or new participants added over time.
Suitable when there is control over every participant in the process, and control over the flow of activities.
Doesn't introduce cyclic dependencies, because the orchestrator unilaterally depends on the saga participants.
Saga participants don't need to know about commands for other participants. Clear separation of concerns simplifies business logic.
Disadvantages of Orchestration Saga Pattern?
Additional design complexity requires an implementation of a coordination logic.
There's an additional point of failure, because the orchestrator manages the complete workflow
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