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Microservices - opportunities, dilemmas and problems


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Presentation from Warsjawa 2014 workshop "Microservices in Scala". Topics covered:
- What are microservices?
- What's the difference between them vs monolithic
- What are the different flavours of microservices?

Published in: Software

Microservices - opportunities, dilemmas and problems

  1. 1. Microservices in Scala workshop by Iterators by Jacek Głodek, Łukasz Sowa and Andrzej Michałowski
  2. 2. Questions we try to answer today: • What are microservices? • What's the difference between them vs monolithic architectures? • What are the different flavours of microservices? • How to use, Play and Akka to do microservices?
  3. 3. Agenda • Short introduction to microservices • Spec of our system • "MS backbone - simple microservices with" talk • Auth and url collection microservices • "Asynchronous views and web services with Play and Akka" talk • Image fetching — reactive deffered job — Play with websockets • "Eventsourcing - total data immutability with akka persistence" talk • Voting made with event sourcing • Ops, testing and monitoring • Summary
  4. 4. Architectures and practices What architectures are we talking about?! Don't think MVC, think MVC web-app run on multiple nodes with load-balancing, memcached cache and Postgres db. What practices are we talking about?! Think TDD, BDD, SOLID, etc.
  5. 5. Code and code-base architecture and practices • programming paradigms • TDD, SOLID, BDD, etc. • Folder structure • Object naming conventions • Separation of concerns • Sharing data in threads
  6. 6. Distributed system architecture • Interfaces, protocols and contracts between modules • System modules • APIs • Deployment strategy • Non-functional guarantees
  7. 7. “Microservices” is a vague term • multiple small apps with REST/HTTP interface, • multiple small apps with deferred message processing • multiple single-file apps with less than 100 lines of code • multiple small apps possibly written in different languages communicating with each other
  8. 8. Microservices • small single-purpose apps with bounded domain enabling polyglot programming + add your favourite ingredients + differences from monolithic architecture © Marivlada | Dreamstime Stock Photos & Stock Free Images
  9. 9. Microservices vs Monolithic architecture Deployment units Monolith Microservices
  10. 10. Microservices vs Monolithic architecture Deployment strategy Monolith Microservices
  11. 11. Microservices vs Monolithic architecture Coupling Monolith Microservices • global variables • messages • function calls • data structures • shared memory • multiple levels of indirection managed with • SOLID, encapsulation and other practices • dependency injection, etc. • different protocols • shared DB’s • shared message queues managed with • contracts
  12. 12. Microservices vs Monolithic architecture Interfaces vs Contracts Monolith Microservices • written with code and shared interfaces within code packages and libraries • checked by tests or compilers (?) • type validations • api calls defined by the language • encapsulation, single-responsibility rule, etc. Problems: • meta-programming, monkey-patching, global state and workarounds. • spoken / unspoken • should be defined on “paper” • defined by protocols, and technologies used, like: • http, websockets, RPC, rabbitMQ, shared MongoDB or Redis, etc. ) Problems: • changing contract or having no contract requires changing multiple services. • multiple API versions without easy solution for validating consistency
  13. 13. Programming microservices
  14. 14. Small single purpose code • Low complexity • No code-level coupling with other modules • “this big” or one hundred lines of code • Easy to rewrite • Rewrite instead of refactor • Easy to spot inputs and outputs • Still requires readable logic
  15. 15. Relevant metrics • Measuring business performance using relevant metrics • Visualisation • Ex. Kamon, custom charts Ex: • forms processed, • mails sent, • PDF invoices generated • performance metrics: • response times • queue sizes • ex. New Relic, etc.
  16. 16. Continuous deployment with hot swapping Having all the metrics: • You can deploy continuously • You can test the service by deploying new and old versions concurrently. • Given enough fail-safety contracts, you can test in production • One service down shouldn’t break whole architecture
  17. 17. Polyglot programming
  18. 18. Problems and dilemmas
  19. 19. Problems and Dilemmas • synchronous and asynchronous processing • guarantees and SLAs • shared and private databases • making layers of micro services • bare-metal vs platforms • data-driven systems, eventsourcing and real-time messaging
  20. 20. Synchronous vs Asynchronous processing Synchronous processing • immediate responses • fast and hard failure • “asking” • request timeouts • problematic to debug series of request Ex. chain of HTTP request and getting 200 Success response Asynchronous processing • posting jobs to be processed • tell don’t ask • fire and forget • need of pooling or waiting for response • longer jobs • failures can be recovered from! Ex. uploading a video file to be processed and getting “Video uploaded successfuly” response.
  21. 21. Guarantees and SLA’s Is clicking like button same as performing bank transfer? Do we really need full ACID DB for holding chat messages? Will it perform fast enough to serve thousand of clients concurrently without building whole cluster of DB’s? 100% consistency and synchronicity is not possible to achieve in distributed system without introducing system wide locks. System-wide locks affect performance a lot, while we try to achieve reactive and scalable system. In microservices we can keep different parts of system with different guarantees and different approaches
  22. 22. Shared vs private databases Shared database • pretty strong contract • convenient for simple domain problems • easier to maintain • problems: • coupling too many services, too deeply. • can become performance bottle-neck Private databases • useful for decoupling and reuse • useful for performance • useful for embedding in microservices that abstract complicated domain models • difficult to maintain, although can many databases can work on single db cluster/instance. • useful for giving microservice authority over some data • problems: • data sharding
  23. 23. Layers of micro services frontend, public facing micro services, background workers and services
  24. 24. Layers of micro services frontend issues • CORS (Cross Origin Resource Sharing) • Rendering of HTML: server-side or in javascript • Moving caches to CDN • Keeping modularity and reusability also on the frontend side • One backend microservice failure shouldn’t break whole frontend.
  25. 25. Layers of micro services user facing services issues • CORS • Versioning of API • Authentication • Caching • Loadbalancing • Security
  26. 26. Layers of micro services internal services • Security • Scalability • Monitoring for failures • Keeping the data consistent • Garbage-in garbage-out
  27. 27. Platform abstraction level bare-metal servers vs platforms Higher level framework = more difficult polyglot programming + easier maintenance + possible code sharing + more tight coupling opportunities
  28. 28. Stateful databases vs eventsourcing Stateful databases • State stored in the database • Ex. “John has $3122 USD on his account” • Transactions and locks that enable us to mutate the state Eventsourcing • No state just events. • Ex. “John got spent $12 USD” • State is inferred from the past events… • Every situation can be replayed! • Events are immutable = no problem with locking, etc. We can also not care about keeping the data at all.
  29. 29. … and other dilemmas. But…
  30. 30. Why not mix all the approaches?
  31. 31. Can sole database be a microservice?
  32. 32. Must microservice be based on REST interfaces?
  33. 33. How would you model microservices for the last system you developed?
  34. 34. That’s it for the intro Thanks!
  35. 35. Summary Microservices come in different flavours:! sync, async, rest, mq, databases, events, hard and easy guarantees, with private and shared databases, based on bare-metal machines and high level platforms. © Marivlada | Dreamstime Stock Photos & Stock Free Images
  36. 36. Summary Spray is great foundation: for simple HTTP services for connecting with awesome Akka processing framework with great directives for strictly defining what requests get processed with great marshalling and serialisation who make simple easy and abstractable
  37. 37. Summary Play is has some useful elements: ! nice routing DSL, nice controller with Action composing nice Websockets with Akka actors lots of libraries to integrate to big boilerplate
  38. 38. Summary Akka is great for messaging, makes concurrent programming easy! ! Actors are not threads Messages and Questions with timeouts Scheduling Watch not to make bloated — keep it single purpose
  39. 39. Summary Eventsourcing ! ! Don’t store mutable state Store immutable events Rebuild state by processing the past events Akka persistance stores the events for you in a journal of choice (Mongo, Redis, Postgres, Maria, Mysql)
  40. 40. What haven’t we talked about ! JVM microframeworks — Finagle, etc. Frontend — how to keep modularity, where to generate HTML, how to handle caching. Monitoring — health checks and metrics (spray directives?) and monitoring front end DevOps — How to configure loadbalancers, CORS, handling configuration and discovery of microservices, prepare auto-scaling, and handling situations when services fail, or how to make hot swap deployments.
  41. 41. Thanks! Łukasz Sowa @luksow Jacek Głodek @jacekglodek