MicroservicesComboStyle

• What do we think micro services are..
• We want to be able to rewrite services and remove legacy code
  • Make all "objects" separate processes that can run on different machines
  • Rather than single process tight binding between classes
  • We could run two of them on the same box to scale
  • Ability to rewrite each object even using different languages if required
  • Could communicate using direct RPC, e.g. as a fully meshed graph
    • Would require agreement on contracts between objects
    • Not favoured approach
    • "Orchestrated style"
  • Combo Model
    • Tuple Spaces - Immutable data store
    • Objects publish immutable facts to central store
    • Objects can publish requests to store
    • Other objects can publish responses to requests to store
    • Objects interested in responses can take those and relay to end users/devices
    • Basically it's pub/sub
    • Can add other subscribers after the fact and consume existing events
    • Promotes loose coupling
    • "Combo Style"
    • What about large messages, too large to pass round
      • Upload the large payload to a repository e.g. via webservice
      • Publish a "pointer" to the data
    • Why not just do RPC to request data directly
    • How do you handle errors
      • If you don’t get a response in a given time frame there is a problem
      • The client only needs to care the other service wsa unavailable and timed out, it should not concern itself with the specific error
    • How do you handle say an order fulfilment scenario where the micro service handling fulfilment was down when the fulfilment request was sent
      • In our case, each subscriber e.g the OrderProcessingService has its own unique persistent queue of messages it will resume processing when it starts up again
    • How do you "fix" data
      • E.g. order sent with wrong email
      • We want to correct the email without double fullfiilling the order
      • The order fulfilment step needs to be idempotent
      • The email sending service would not be, it would send the confirmation email again regardless
      • Each service will still hold its own state, or have its own database
    • When would you switch a service to use queues/RabbitMQ
• Prediction: 20/09/14 DS: Formal verification of microservices system proof, using COQ? <- fix me