by Richard Rodger- Nodeday Amsterdam Feb 11, 2016

1. Service Discovery
or
Why each microservice should believe it's
the only one in the world.
Richard Rodger
@rjrodger

4. What are microservices?
๏ Small independent processes;
๏ Communicating via messages;
๏ A powerful component model.

5. Why use microservices?
๏ Avoid technical debt;
๏ Get continuous delivery;
๏ Build fast.

6. What are the trade-offs?
๏ Deployment is more complex;
๏ Weird programming model;
๏ Services have to find each other;

10. Configuration Files
๏ Hard code all the locations;
๏ Automate update and reloads;
๏ Surprisingly workable;
๏ But gets messy fast!

11. Intelligent Load Balancing
๏ The load balancer knows where services are;
๏ Services have to register in some way;
๏ Load balancers are yet more things to manage;
๏ URL paths are still identifiers!
๏ Examples: Netflix Eureka, nginx, HAProxy

12. Service Registries
๏ Services lookup locations;
๏ Registries can provide health checks;
๏ Registries themselves need to be distributed;
๏ Service A still knows about Service B!
๏ Examples: consul, etcd, zookeeper

13. DNS
๏ Hide services behind domain names;
๏ We know DNS can scale;
๏ More management work;
๏ Service A still knows about Service B!
๏ Examples: Mesos, Weave, SkyDNS

14. Message Bus
๏ Hide services behind topic names;
๏ Nice for publish/subscribe models!
๏ You have to manage the bus;
๏ Rapids, rivers and pools;
๏ Topics are weak identifiers - better!
๏ Examples: Kafka, Rabbitmq, Redis

16. Pattern Matching
Service discovery is an anti-pattern.
Instead, make messages first-class citizens.
Use message data to define patterns,
and these patterns define a language!
Transport Independence
Services should not know about each other,
or how to send messages.
Services are fully defined by:
message patterns that they recognise, and
message patterns that they emit.

17. Blind Messages
๏ Services have zero-knowledge of other services;
๏ Services emit messages into the world;
๏ Services let the world know what they care about;
๏ The underlying infrastructure handles identity;
๏ Works with any of the service discovery methods!

18. Peer-to-peer
๏ Knowledge of identity can be distributed;
๏ Each service maintains a local view of world,
and updates this view as services come and go;
๏ Mapping from message to destination is not
exposed to developers.

19. SWIM
๏ "Scalable Weakly-consistent Infection-style
Process Group Membership Protocol"
๏ https://www.cs.cornell.edu/~asdas/research/dsn02-swim.pdf
๏ Designed for large scale (used by Uber);
๏ Basic idea:
๏ each service pings a random subset of other
services, different each time
๏ the pings establish health and disseminate
membership information

23. // a search message
{
"role": "search", // a namespace
"cmd": "search", // this is a command
"query": "ldap", // some data
}
!
// the pattern to match
role:search,cmd:search

24. // some nodezoo message patterns
!
role:search,cmd:search // do a search
role:search,cmd:insert // insert into index
role:info,cmd:get // get module info
role:npm,cmd:get // get npm data
role:npm,info:change // module changed!
role:info,req:part // need module info
role:info,res:part // here's module info
!
!
!

25. role:search,cmd:search
role:info,cmd:get
synchronous request/response

26. role:npm,info:change
asynchronous "winner-take-all"
(actor)

27. role:info,req:part
asynchronous "fire-and-forget"
(publish/subscribe)
role:info,res:part

28. asynchronous "fire-and-forget"
(publish/subscribe)
synchronous request/response
asynchronous "winner-take-all"
(actor)
synchronous "sidewinder"
(side effects!)
synchronous/
asynchronous
consumed/
observed

29. // nodezoo-web
IN:
none
OUT:
role:search,cmd:search // sync
role:info,cmd:get // sync
// nodezoo-search
IN:
role:search,cmd:search // sync
role:search,cmd:insert // async
OUT:
none
service specification

30. // nodezoo-info
IN:
role:info,cmd:get // sync
role:info,res:part // async
OUT:
role:info,req:part // async
// nodezoo-npm
IN:
role:npm,cmd:get // sync
role:npm,info:change // async
role:info,req:part // async
OUT:
role:info,res:part // async
service specification

31. // role:search,cmd:search
consumed:
nodezoo-web -> nodezoo-search
// role:info,cmd:get
consumed:
nodezoo-web -> nodezoo-info
// role:npm,info:change
observed:
nodezoo-update -> nodezoo-npm
service interactions

32. // role:info,req:part
observed:
nodezoo-info -> nodezoo-npm
nodezoo-info -> nodezoo-github
// role:info,res:part
observed:
nodezoo-npm -> nodezoo-info
nodezoo-github -> nodezoo-info
service interactions

33. senecajs.org

34. Code!
github.com/rjrodger/nodezoo

35. Thanks!
Richard Rodger
@rjrodger
richardrodger.com
senecajs.org
github.com/apparatus/fuge