Reactive Microsystems The Evolution of Microservices at Scale - PowerPoint PPT Presentation

vs Commands Events 1. Intentless 1. All about intent

vs Commands Events 1. Intentless 1. All about intent 2. Directed 2. Anonymous

vs Commands Events 1. Intentless 1. All about intent 2. Directed 2. Anonymous 3. S ingle addressable 3. Just happens - for destination others (0-N) to observe

vs Commands Events 1. Intentless 1. All about intent 2. Directed 2. Anonymous 3. S ingle addressable 3. Just happens - for destination others (0-N) to observe 4. Models personal 4. Models broadcast communication (speakers corner)

vs Commands Events 1. Intentless 1. All about intent 2. Directed 2. Anonymous 3. S ingle addressable 3. Just happens - for destination others (0-N) to observe 4. Models personal 4. Models broadcast communication (speakers corner) 5. Distributed focus 5. Local focus

vs Commands Events 1. Intentless 1. All about intent 2. Directed 2. Anonymous 3. S ingle addressable 3. Just happens - for destination others (0-N) to observe 4. Models personal 4. Models broadcast communication (speakers corner) 5. Distributed focus 5. Local focus 6. Command & Control 6. Autonomy

Let the Events Define the Bounded Context

Are we done now? Perhaps. We have come a long way. But events can also be used for: ➡ Persistence ➡ Managing time

Event Based Persistence

“Update-in-place strikes systems designers as a cardinal sin: it violates traditional accounting practices that have been observed for hundreds of years.” - jim Gray The Transaction Concept, Jim Gray (1981)

Event Logging The Bedrock

“The truth is the log. The database is a cache of a subset of the log.” - Pat Helland Immutability Changes Everything, Pat Helland (2015)

The Log A Database Of the Past Not Just the Present

Event Sourcing A Cure For the Cardinal Sin

Event Sourced Services

Event Sourced Services Happy Path

Event Sourced Services 1) Receive and verify Command Happy Path (“ApprovePayment”)

Event Sourced Services 1) Receive and verify Command 2) Create new Event Happy Path (“ApprovePayment”) (“PaymentApproved”)

Event Sourced Services 1) Receive and verify Command 2) Create new Event 3) Append Event Happy Path (“ApprovePayment”) (“PaymentApproved”) to Event Log

Event Sourced Services 1) Receive and verify Command 2) Create new Event 3) Append Event 4) Update internal Happy Path (“ApprovePayment”) (“PaymentApproved”) to Event Log component state

Event Sourced Services 1) Receive and verify Command 2) Create new Event 3) Append Event 4) Update internal 5) Run side-effects Happy Path (“ApprovePayment”) (“PaymentApproved”) to Event Log component state (approve the payment)

Event Sourced Services 1) Receive and verify Command 2) Create new Event 3) Append Event 4) Update internal 5) Run side-effects Happy Path (“ApprovePayment”) (“PaymentApproved”) to Event Log component state (approve the payment) SAD Path - recovering from failure