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Microservicessystem_design~12 mins

Event replay in Microservices - Architecture Diagram

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System Overview - Event replay

This system allows replaying past events in a microservices architecture to rebuild state or recover from errors. It stores events in an event store and replays them to services that consume these events, ensuring data consistency and fault tolerance.

Architecture Diagram
User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  v
Event Producer Service ---> Event Store (Event Log) <--- Event Replay Service
                                   |
                                   v
                            Consumer Services
                                   |
                                   v
                               Database
                                   |
                                   v
                                 Cache
Components
User
client
Initiates actions that generate events
Load Balancer
load_balancer
Distributes incoming requests evenly to API Gateway instances
API Gateway
api_gateway
Routes requests to appropriate microservices
Event Producer Service
service
Generates and publishes events to the event store
Event Store (Event Log)
event_store
Stores all events in order for replay and auditing
Event Replay Service
service
Reads events from the event store and replays them to consumer services
Consumer Services
service
Processes events to update state and business logic
Database
database
Stores the current state updated by consumer services
Cache
cache
Speeds up read operations by storing frequently accessed data
Request Flow - 9 Hops
User → Load Balancer
Load Balancer → API Gateway
API Gateway → Event Producer Service
Event Producer Service → Event Store (Event Log)
Event Store (Event Log) → Event Replay Service
Event Replay Service → Consumer Services
Consumer Services → Database
Consumer Services → Cache
Cache → User
Failure Scenario
Component Fails:Event Store (Event Log)
Impact:New events cannot be stored, so event replay and state updates stop. Consumer services do not receive new events, causing stale data.
Mitigation:Use event store replication and backups to restore quickly. Consumer services can continue reading from cache but will have stale data until event store recovers.
Architecture Quiz - 3 Questions
Test your understanding
Which component is responsible for storing all events for replay?
ALoad Balancer
BCache
CEvent Store (Event Log)
DAPI Gateway
Design Principle
This architecture uses an event store as a single source of truth for all events, enabling reliable event replay to rebuild system state. It separates event production from consumption, improving fault tolerance and scalability.