Saga Pattern Architecture
In this tutorial, we are going to discuss about the Saga Pattern Architecture. The Saga Pattern architecture is designed to manage distributed transactions by splitting them into smaller, manageable transactions, each with its own compensating transaction. This architecture can be implemented using either orchestration or choreography.
We’ve discussed what the Saga Pattern is and why it’s essential in distributed systems. We’ve also seen how the pattern works in general. Now, let’s get under the hood and understand the architecture that powers this ingenious pattern. But before we begin, let’s recall that in the world of distributed systems, the Saga Pattern is our “power line” — it’s the element that ensures transactions across different services are consistent and reliable. So, how does it do it?
The Backbone: Local Transactions
A saga is composed of multiple local transactions. Each of these transactions is executed within a single service and its corresponding database. These local transactions form the backbone of the Saga Pattern, akin to the individual sections of a power line. Each local transaction carries its own responsibilities but when strung together, they work towards a common objective — maintaining data consistency across the system.
Remember, every local transaction in a saga has an associated compensating transaction. The compensating transaction is capable of undoing the changes made by its corresponding local transaction. Together, these transactions ensure that even if a step in the saga fails, the system can still maintain its integrity.
Two Approaches: Choreography and Orchestration
As mentioned earlier, there are two types of Saga Patterns – Choreography and Orchestration. These two approaches represent the architectural choices you have when implementing the Saga Pattern. They differ in how they coordinate the execution of the local transactions in a saga.
In the Choreography Saga Pattern, each service knows which service to call next in the saga. It’s a decentralized approach, with no single point of orchestration. Imagine an ant colony, where each ant knows its tasks and performs them without being explicitly told to do so. The colony functions smoothly as a result of each ant playing its part.
In contrast, the Orchestration Saga Pattern involves a central coordinator, or an orchestrator, which guides the saga’s execution. Think of it as a busy airport with an air traffic controller. The controller guides each airplane (service) when to take off (start a transaction) and when to land (end a transaction) to ensure smooth operation.
So, should you be the ant or the air traffic controller? The answer largely depends on your use-case and the complexity of your business transaction. While choreography may offer more autonomy to your services, orchestration can provide you more control and easier error handling.
The Heart of the Matter: Eventual Consistency
At the heart of the Saga Pattern is the concept of eventual consistency. It’s a consistency model that’s more suited to distributed systems. Unlike ACID transactions, which promise immediate consistency, the Saga Pattern ensures that the system will eventually reach a consistent state, even if it goes through inconsistent states in the process.
This can be likened to juggling. At any given moment, some balls (or transactions) are in the air (being processed), but a skilled juggler (the Saga Pattern) ensures that eventually, all balls will be handled correctly without dropping.
Handling Failures: Compensating Transactions
The saga has a built-in mechanism to handle failures — the compensating transactions. If a local transaction fails, the saga executes compensating transactions for the previously successful local transactions. This brings the system back to a consistent state.
To picture this, imagine walking on a path and realizing you’ve gone the wrong way. What do you do? You retrace your steps to the point where you took the wrong turn. That’s what compensating transactions do. They “undo” the changes to get the system back to the point before the error occurred.
Pit Stops: Saga Log
To keep track of the saga’s progress and state, a saga log is maintained. This log records every local transaction and compensating transaction executed in the saga. In our city analogy, think of the saga log as the city blueprint. It gives a detailed view of what has been done and what needs to be done next.
The Inner Workings of the Saga Pattern
Now that we’ve explored the architecture of the Saga Pattern, let’s delve deeper into how the magic happens, how this pattern manages to maintain data consistency in complex distributed systems. This tutorial will be your “behind the scenes” tour, revealing the inner workings of the Saga Pattern.
A Saga’s Life Journey: The Sequence of Transactions
A saga is essentially a sequence of local transactions. Each transaction is like a step in a journey. But remember, the Saga Pattern is not just about taking those steps; it’s also about knowing when to step back.
What does this mean? Each local transaction has a corresponding compensating transaction. If a transaction fails, the compensating transactions for the previous local transactions are executed. This “step back” process ensures the system’s eventual consistency.
Imagine you’re setting up dominos. Each domino is a local transaction. If one domino falls prematurely, you stop the sequence and reset the fallen dominos—that’s your compensating transaction.
The Role Players: Services, Orchestrator, and Choreographer
In the Saga Pattern, there are key role players—services, the orchestrator (in an Orchestration Saga), and the choreographer (in a Choreography Saga).
Services are the basic units that carry out local transactions. In the Orchestration Saga, an orchestrator guides the services, dictating the order of transactions. The orchestrator is like the conductor of an orchestra, ensuring every instrument (service) plays at the right time to create a harmonious symphony (consistent data).
In the Choreography Saga, services independently decide the flow of transactions. There’s no central conductor here. Instead, each service is like a dancer who knows their steps and performs in sync with the others.
Breaking the Monolith: Service Independence
One crucial aspect of the Saga Pattern is that it enables services to remain independent of each other. Each service owns its database, ensuring that the failure of one service doesn’t directly impact the others. This principle, also known as database per service, prevents a single point of failure in the system, making it more robust and reliable.
Picture this as a team of rock climbers, each with their own safety ropes. If one climber slips, they can be caught by their rope without causing the rest to fall. In the same way, each service in a saga has its own “safety rope”—its own database, making the whole system more resilient.
Remembering the Steps: The Saga Log
The Saga Log is a critical component that tracks the saga’s progress. It records all the local transactions and compensating transactions that have been executed. This log serves as a memory of the saga, helping it resume from where it left off in case of a failure.
Think of the saga log as a breadcrumb trail left by Hansel and Gretel in the classic fairy tale. If they were to get lost (a system failure), they could follow the breadcrumbs (saga log) back home (consistent state).
The End Game: Eventual Consistency
The ultimate goal of the Saga Pattern is to achieve eventual consistency. This means the system may go through inconsistent states, but it will eventually reach a consistent state. It’s like surfing. There may be highs and lows, but a skilled surfer can ride the waves and reach the shore safely.
Handling the Unexpected: Compensating Transactions
Despite the best planning, things can go wrong. That’s why the Saga Pattern includes compensating transactions. When a local transaction fails, the saga executes compensating transactions to “undo” the changes made by the previous local transactions. It’s the saga’s way of saying, “No worries. We’ve got this covered.”
The Saga Pattern architecture is highly effective for managing distributed transactions, especially in microservices environments, providing a robust solution for ensuring data consistency and fault tolerance.
That’s all about the Saga Pattern Architecture. If you have any queries or feedback, please write us email at contact@waytoeasylearn.com. Enjoy learning, Enjoy Microservices..!!.!!