I Used Event Sourcing for 6 Months: 5 Lessons for 2025

Event Sourcing. The name itself sounds powerful, doesn't it? It conjures images of perfect audit trails, a god-like ability to "time travel" through your application's state, and a beautiful, decoupled architecture. Six months ago, my team and I were captivated by this promise. We were building a new logistics platform, and the idea of capturing every single business event as our source of truth felt like the "right" way to do it. So, we dove in headfirst.

Now, on the other side of that initial sprint, I’m here to share the view from the trenches. Event Sourcing is one of the most intellectually stimulating patterns I've ever worked with. It’s also one of the most demanding. If you're considering it for your next project in 2025, grab a coffee. Let’s talk about what the brochures don't tell you.

Lesson 1: Your Domain is the Deciding Factor

This is the most crucial lesson, so it comes first. Event Sourcing is not a general-purpose architecture. It’s a specialized tool for a specific type of problem. Applying it to the wrong domain is like using a sledgehammer to hang a picture frame—messy, excessive, and you’ll probably break the wall.

So, what's a good fit? Domains where the sequence of events is more important than the current state. Think about:

• E-commerce: OrderPlaced, PaymentProcessed, ItemShipped, OrderDelivered.
• Banking: AccountOpened, DepositMade, WithdrawalAttempted, TransferCompleted.
• Insurance: ClaimFiled, EvidenceSubmitted, AssessmentCompleted, ClaimApproved.

In these scenarios, the "why" and "how" we got to the current state is critical business information.

Conversely, if your application is mostly CRUD (Create, Read, Update, Delete) forms, ES is massive overkill. A user profile page where you just update an email address? Storing UserEmailUpdated events is far more complex than a simple UPDATE users SET email = '...'.

The first rule of Event Sourcing club is: seriously discuss if you actually need to be in the club. If the history of state changes isn't a core business requirement, you can likely achieve your goals with a much simpler audit log on a traditional state-based system.

Lesson 2: Projections Are Your New Best Frenemy

In a traditional system, you write to a table and you read from that same table. Simple. With Event Sourcing, you write events to an append-only log. But you can't query an event log efficiently to answer questions like, "Show me all active orders for customer X."

This is where projections (or read models) come in. You create listeners that process the event stream and build optimized models for querying. My OrderPlaced event might update a customer_orders table, an inventory_levels document, and a sales_dashboard metric.

Initially, this feels amazing. "Wow, I can create any view of the data I want, just by listening to events!" But this initial joy quickly gives way to a new set of challenges.

The Reality of 'The Replay'

The sales pitch for projections is that if you need a new read model, you just "replay all the events" and build it. This works beautifully when you have a thousand events. What about when you have 100 million? Replaying the entire history of your application can take hours or even days. It's not an instant, magical operation.

You quickly realize you need strategies to manage this:

• Snapshots: Periodically, you save the full state of an aggregate so you don't have to replay events from the very beginning.
• Versioning: What happens when you change the structure of an event? You can't just change the old ones. You need to write code that can handle OrderPlaced_v1, OrderPlaced_v2, and so on. This adds significant cognitive load.
• Eventual Consistency: Your read models are, by nature, eventually consistent. The write happens, the event is published, and then the projection is updated. For most UIs, this is fine. But for workflows that need read-your-writes consistency, you have to build clever workarounds.

Projections give you incredible flexibility, but they are not free. Each one is a new micro-service you have to build, deploy, and maintain.

Lesson 3: The Tooling Tax is Real and It's Expensive

Adopting Event Sourcing isn’t a single decision; it’s a commitment to a whole new ecosystem of tools and concepts. Unlike a simple web framework with a connected database, an ES system has many more moving parts.

Event Sourcing doesn't just change your database; it changes everything around your database.

Here’s a non-exhaustive list of what you'll suddenly find yourself needing:

• An Event Store: This is more than just a database table. You need optimistic concurrency control, the ability to read streams forwards and backwards, and subscription mechanisms. We used a relational database at first, and while possible, we quickly saw the appeal of dedicated tools like EventStoreDB or using Kafka as a log.
• Serialization Format: How are your events stored? JSON is easy to start with, but it’s verbose and schema evolution can be a pain. Protobuf or Avro are more robust but add another layer of compilation and tooling.
• Message Bus: How do events get from the event store to the projections? You'll likely need something like RabbitMQ or Kafka Connect to manage this reliably.
• Debugging Tools: This was a huge one for us. In a state-based system, you can just SELECT * FROM products WHERE id = 123 to see the current state. In ES, the state is an in-memory construct derived from a stream of events. You need custom tooling to easily visualize the current state of an aggregate or trace how it was built.

This "tooling tax" means your team's velocity will likely take a nosedive initially as you build out and learn this new infrastructure.

Lesson 4: CQRS Isn't Optional; It's Inevitable

Command Query Responsibility Segregation (CQRS) is a pattern where you separate the model for writing data (commands) from the model for reading data (queries). People often talk about ES and CQRS in the same breath, and for a good reason.

While you could theoretically do Event Sourcing without CQRS (e.g., by replaying and calculating state on every read request), it would be horrendously inefficient. In practice, the moment you create your first projection, you've implemented CQRS.

This separation is powerful but doubles the conceptual surface area of your system:

You are no longer managing one data model; you are managing two distinct models, plus the transformation logic that connects them. This is a fundamental mind-shift. Your developers can't just think about "the order model" anymore. They have to think about "the order write model" and "the order read model."

Lesson 5: 'Time Travel' Is More of an Archaeological Dig

One of the most hyped benefits of Event Sourcing is "time travel"—the ability to debug issues by replaying events to see exactly what the application state was at a specific moment.

This is absolutely possible, and it's an incredibly powerful debugging tool. We used it to solve a gnarly bug involving a race condition that would have been nearly impossible to reproduce otherwise. However, it's not the simple, push-button feature you might imagine. It’s more like a careful archaeological dig.

Here's why:

• Code Evolution: The code that interprets your events changes over time. To accurately reconstruct the state from six months ago, you might need to run the version of the code from six months ago. This requires disciplined source control and deployment strategies.
• External Interactions: What if an event triggered an email or a call to a third-party payment gateway? Replaying that event will try to trigger that side-effect again unless you build your system to distinguish between a "live" run and a "replay" run.
• It’s a Developer Tool: Unless you invest a massive amount of effort, time travel is a debugging and forensics tool for your technical team, not a user-facing feature. Don't promise your business stakeholders that they can "rewind the business" without understanding the immense complexity involved.

It provides an unparalleled audit log, but treating it as a literal time machine is a path to disappointment.

Conclusion: So, Should You Use Event Sourcing in 2025?

After six months, my perspective on Event Sourcing has shifted from wide-eyed evangelism to pragmatic respect. It's a pattern of immense power, but that power comes with a hefty price in terms of complexity, cognitive overhead, and tooling.

Here's my advice for 2025:

1. Validate the Domain: Don't even think about ES unless your core domain is inherently event-driven and the history of "what happened" is a first-class business asset.
2. Start Small: Don't rewrite your monolith using ES. Identify a single, isolated service (a bounded context) that is a perfect fit and build a prototype. Feel the pain and the power on a small scale first.
3. Respect the Overhead: Acknowledge that you're not just choosing a persistence strategy; you're choosing an entire architectural style. Budget time for building infrastructure, tooling, and, most importantly, team knowledge.

Event Sourcing solved some very hard problems for our logistics platform in ways that a traditional CRUD system couldn't have. But it also introduced a new class of problems we had to solve. It’s not a silver bullet, but for the right kind of wound, it's an incredibly effective, if complex, medicine.