With a microservices arhcitecture system behaviour gets spread out across many, many narrowly focused microservices. Much of the functionality in the system depends on those services collaborating. In this talk I explore different modes of collaboration between microservices, how they compare, which are preferable, and how to keep it all simple. Along the way I will show how to use HTTP for the different types of collaboration and how to use Nancy to implement them on top of ASP.NET Core. Video of the talk given at the DotNext conference https://www.horsdal-consult.dk/2018/05/talk-lightweight-microservice.html

1. LIGTHWEIGHT MICROSERVICE
COLLABORATION USING HTTP
CHRISTIAN HORSDAL
@CHR_HORSDAL

2. ABOUT ME
Christian Horsdal
Independent Consultant
www.horsdal-consult.dk
c.horsdal@gmail.com
@chr_horsdal

3. 3
MICROSERVICES

4. INTRODUCTION TO MICROSERVICES
A MICROSERVICE IS A SERVICE WITH ONE, AND ONLY
ONE, VERY NARROWLY FOCUSED CAPABILITY THAT A
REMOTE API EXPOSES TO THE REST OF THE SYSTEM.

5. INTRODUCTION TO MICROSERVICES

6. WHY MICROSERVICES?
• ENABLES CONTINUOUS DELIVERY
• HIGHLY MAINTAINABLE SERVICES
• EFFICIENT DEVELOPER WORKFLOW
• ROBUST BY DESIGN
• FLEXIBLE SCALABILITY

7. WHY NOT?
• DISTRIBUTED SYSTEMS ARE HARD
• 100S OR MORE SERVICES
 COMPLEX PRODUCTION ENVIRONMENT
 LOTS OF DEPLOYMENTS
• REFACTORING ACROSS SERVICES IS CUMBERSOME

8. MICROSERVICE COLLABORATION

9. COLLABORATION IS ANY AND ALL
COMMUNICATION BETWEEN MICROSERVICES

10. COLLABORATION STYLESS
• COMMANDS
• DOSTUFF
• QUERIES
• READSTUFF
• EVENTS
• STUFFHAPPENED

11. EXAMPLE

12. COMMANDS AND QUERIES

13. COMMANDS AND QUERIES
• SYNCHRONOUS
• QUERIES: HTTP GET
• COMMANDS: HTTP POST, HTTP PUT

14. EXAMPLE: COMMANDS, QUERIES

15. EXAMPLE: QUERY
Get("/{userId:int}", parameters =>
{
int userId = parameters.userId;
if (registeredUsers.ContainsKey(userId))
return registeredUsers[userId];
else
return HttpStatusCode.NotFound;
});

16. EXAMPLE: COMMAND
Post("/", _ =>
{
var newUser = this.Bind<LoyaltyProgramUser>();
this.AddRegisteredUser(newUser);
return this.CreatedResponse(newUser);
});

17. DEMO

19. EVENTS
• ASYNCHRONOUS
• “STUFF HAPPENED”
• PAST TENSE
• PUBLISH/SUBSCRIBE

20. EXAMPLE: EVENTS

21. EVENT FEED
• AN HTTP GET ENDPOINT
• SUPPORTS PAGING
• HTTP GET /EVENTS?FROM=100&TO=200
• EVENTS RAISED BY DOMAIN LOGIC
• EVENTS ARE STORED IN AN EVENT STORE

22. EXAMPLE: EVENT FEED
Get("/", _ =>
{
long firstEventSequenceNumber, lastEventSequenceNumber;
if (!long.TryParse(this.Request.Query.from.Value,
out firstEventSequenceNumber))
firstEventSequenceNumber = 0;
if (!long.TryParse(this.Request.Query.to.Value,
out lastEventSequenceNumber))
lastEventSequenceNumber = long.MaxValue;
return eventStore.GetEvents(firstEventSequenceNumber,
lastEventSequenceNumber);
});

23. SUBSCRIBING TO EVENTS
Fetch
events
Parse
events
Process
events
Save max
event
number
Sleep

24. SUBSCRIBING TO EVENTS
• PART OF A MICROSERVICE
• BUT SEPARATE PROCESS

25. DEMO

26. EXAMPLE RECAP

27. COLLABORATION STYLES
• COMMANDS
• DOSTUFF
• QUERIES
• READSTUFF
• EVENTS
• STUFFHAPPENED

28. COLLABORATION STYLES
• COMMANDS & QUERIES
• SYNCHRONOUS
• CALLER SEES ERRORS
• CALLER IS RESPONSIBLE FOR SUCCESS
• CONSISTENCY
• COUPLING BY CONTRACT
• COUPLING TEMPORALLY

29. COLLABORATION STYLES
• EVENTS
• ASYNCHRONOUS
• SUBSCRIBERS SEE ERRORS
• SUBSCRIBERS ARE RESPONSIBLE FOR SUCCESS
• EVENTUAL CONSISTENCY
• COUPLING BY CONTRACT
• NO TEMPORAL COUPLING

31. PREFER EVENT BASED COLLABORATION

32. ABOUT ME
Christian Horsdal
Independent Consultant
www.horsdal-consult.dk
c.horsdal@gmail.com
@chr_horsdal

33. LINKS
• MY BLOG: WWW.HORSDAL-CONSULT.DK
• MY MICROSERVICES BOOK: WWW.MANNING.COM/BOOKS/MICROSERVICES-IN-NET-CORE
• THE POLLY LIBRARY: GITHUB.COM/APP-VNEXT/POLLY