It’s Not Just Request/Response: Understanding Event-driven Microservices
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The document discusses event-driven microservice architectures as an alternative to traditional request/response microservice patterns. It describes how each microservice can operate independently by broadcasting state changes as events, rather than making direct requests to other services. This allows services to have autonomous control loops and respond immediately to requests if they are already aware of the necessary data states. The approach derives the CQRS pattern of separating query and command handling. It also advocates for an event store to decouple services and act as a message bus to distribute events.
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It’s Not Just Request/Response: Understanding Event-driven Microservices
- 1. © Copyright 2018 Pivotal Software, Inc. All rights Reserved. Version 1.0 Cornelia Davis Sr. Director of Technology, Pivotal @cdavisafc February 2018 It’s not Just Request/Response: Understanding Event-driven Microservices
- 2. Where we’re going today Familiar Event-driven Scenarios Usual Microservices Architectures Autonomy Event-driven Microservices Architectures Event-sourcing
- 3. Cover w/ Image Me? Developer (wasn’t Ops) Web architectures for >10 years Cloud-native for 5+ years Cloud Foundry for 5+ years https://www.manning.com/books/cloud-native @cdavisafc
- 4. Event-driven Scenarios The ones we readily think of …. this is not what I want to talk about today
- 5. …usually Request/Response Instead, I want to talk about the implementations that are…
- 8. Assumption: Each microservice boasts 99.999% availability (and there are 100 of them) Assumption: The network is reliable Result: Home Page achieves 99.9% availability https://en.wikipedia.org/wiki/Fallacies_of_distributed_computing
- 9. How we try to add a level of resilience:
- 10. Retries ▸ Client must consider failure ▸ Decide on fall-back behavior ▸ Likely including retries ▸ But then we need to handle downstream consequences of these (retry) behaviors CLIENT SERVICE Timeouts? If we don’t hear back, try again
- 11. Circuit Breakers ▸ This is your protection against DDOSing yourself https://martinfowler.com/bliki/CircuitBreaker.htmlhttps://martinfowler.com/bliki/CircuitBreaker.html
- 12. But then, is stale data better than no data - often it is ▸ Client must consider failure ▸ Decide on fall-back behavior ▸ Likely including caches ▸ But then we need to handle things like cache expiry SERVICE APP SERVICE APP APP SERVICE APP SERVICE APP SERVICE APP
- 13. But all of these patterns make the assumption of Request/Response I want to challenge that base assumption
- 14. Autonomy It’s not the size of a “micro”service, but rather its autonomy µService Client µService ! response " request Request/Response µService ! outcome" event Event-driven
- 16. ! " # $ % & Connections’ Posts API Abundant Sunshine Your source for healthy cooking New From Your Network Seasonal Response Response Response Request Request Request Connections API User: - id - username - name Connections: - id - follower - followed Posts API Posts: - id - date - userId - title - body Starting with the familiar
- 17. Connections’ Posts API Abundant Sunshine Your source for healthy cooking New From Your Network Seasonal Connections API Posts API User: - id - username - name Connections: - id - follower - followed Posts: - id - date - userId - title - body Turning that on its head
- 18. Connections’ Posts API Abundant Sunshine Your source for healthy cooking New From Your Network Seasonal Connections API Posts API User: - id - username - name Connections: - id - follower - followed Posts: - id - date - userId - title - body
- 19. Connections’ Posts API Abundant Sunshine Your source for healthy cooking New From Your Network Seasonal Connections API Posts API User: - id - username - name Connections: - id - follower - followed Posts: - id - date - userId - title - body Response Request When the request comes in, the Connections’ Post service already has the answer!
- 20. Connection’s Posts API Abundant Sunshine Your source for healthy cooking New From Your Network Seasonal Connections API Posts API User: - id - username - name Connections: - id - follower - followed Posts: - id - date - userId - title - body Posts: - userId - date - title Response Request Connections: - id - follower - followed User: - id - username - name
- 21. µService New from Connections ! response " request ! outcome " event Request/Response Event-driven µService Client µService Posts
- 22. Connections’ Posts API Abundant Sunshine Your source for healthy cooking New From Your Network Seasonal Connections API Posts API Response Request Whenever something changes in the network of user connections, the “Connections” API broadcasts the change event - any interested parties (including the “Connections’ Posts” API) can do with they wish Whenever new posts are available, the “Posts” API broadcasts the change event - any interested parties (including the “Connections’ Posts” API) can do with it they wish The New from Connections microservice handles events as they occur. Javascript in the browser makes HTTP request to the “New from Network” API, providing a userID. While the response may be expected asynchronously, the API protocol is request/ response. The “Connections’ Posts” API can respond immediately because it already knows about the state of the data it is responsible for.
- 23. Connections’ Posts API Abundant Sunshine Your source for healthy cooking New From Your Network Seasonal Connections API Posts API Response Request Whenever something changes in the network of user connections, the “Connections” API broadcasts the change event - any interested parties (including the “Connections’ Posts” API) can do with they wish 1 Whenever new posts are available, the “Posts” API broadcasts the change event - any interested parties (including the “Connections’ Posts” API) can do with it they wish 1 1 The New from Connections microservice handles events as they occur. Javascript in the browser makes HTTP request to the “New from Network” API, providing a userID. While the response may be expected asynchronously, the API protocol is request/ response. The “Connections’ Posts” API can respond immediately because it already knows about the state of the data it is responsible for. 1 2
- 24. Connections’ Posts API Abundant Sunshine Your source for healthy cooking New From Your Network Seasonal Connections API Posts API Response Request Whenever something changes in the network of user connections, the “Connections” API broadcasts the change event - any interested parties (including the “Connections’ Posts” API) can do with they wish 1 Whenever new posts are available, the “Posts” API broadcasts the change event - any interested parties (including the “Connections’ Posts” API) can do with it they wish 1 1 The New from Connections microservice handles events as they occur. Javascript in the browser makes HTTP request to the “New from Network” API, providing a userID. While the response may be expected asynchronously, the API protocol is request/ response. The “Connections’ Posts” API can respond immediately because it already knows about the state of the data it is responsible for. 1 2 Independent Control Loops!!!
- 25. Connections’ Posts API Abundant Sunshine Your source for healthy cooking New From Your Network Seasonal Connections API Posts API Response Request Whenever something changes in the network of user connections, the “Connections” API broadcasts the change event - any interested parties (including the “Connections’ Posts” API) can do with they wish 1 Whenever new posts are available, the “Posts” API broadcasts the change event - any interested parties (including the “Connections’ Posts” API) can do with it they wish 1 1 The New from Connections microservice handles events as they occur. Javascript in the browser makes HTTP request to the “New from Network” API, providing a userID. While the response may be expected asynchronously, the API protocol is request/ response. The “Connections’ Posts” API can respond immediately because it already knows about the state of the data it is responsible for. 1 2
- 26. Connections’ Posts API Response Request 1 The New from Connections microservice handles events as they occur. 2 1 What, then, is the developer writing?
- 27. Connections’ Posts API Response Request 1 The New from Connections microservice handles events as they occur. 2 1 What, then, is the developer writing?
- 28. Connections’ Posts API Response Request 1 The New from Connections microservice handles events as they occur. 2 1 What, then, is the developer writing?
- 29. Connections’ Posts API Response Request 1 The New from Connections microservice handles events as they occur. 2 1 We just derived the CQRS pattern! CQRS = Command Query Responsibility Segregation Handling Queries Handling Commands
- 30. Connections’ Posts API Abundant Sunshine Your source for healthy cooking New From Your Network Seasonal Connections API Posts API Response Request 1 1 1 1 2
- 31. µService Event Consumer µService Event Producer event store … … The Event Store Decouples the Microservices
- 32. Connections’ Posts API Abundant Sunshine Your source for healthy cooking New From Your Network Seasonal Connections API Posts API Response Request 1 1 1 1 2 event store … …
- 33. Connections’ Posts API Abundant Sunshine Your source for healthy cooking New From Your Network Seasonal Connections API Posts API Response Request 1 1 1 1 2 event store … …
- 34. Summary Imperative programming model not ideal for distributed systems → functional models better Event-driven architectures bring autonomy → Independent control loops Microservices have their own data stores Retries, Circuit-breakers and cache with expiry are replaced by CQRS programming patterns Events-stores are the “message busses” of the event- driven approach
- 35. Transforming How The World Builds Software © Copyright 2017 Pivotal Software, Inc. All rights Reserved.
- 36. Cover w/ Image https://www.manning.com/books/cloud-native @cdavisafc All of this is described, with code samples, in chapter 4 (available through MEAP)