150 lines
4.1 KiB
Markdown
150 lines
4.1 KiB
Markdown
# Backend Thinking
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## Backend Role
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Transform business requirements to action, which usually involves:
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- Service:
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- ZaloPay use microservices architecture, mostly written using Go and Java
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- API:
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- HTTP (Client-Server) and GRPC (Server-Server)
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- Database/Cache/Storage/Message Broker
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- MySQL/Redis/S3/Kafka
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- CRUD
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- Docs
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- Mostly design notes and diagrams which show how to implement business
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requirements
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After successfully do all of that, next step is:
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- Testing
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- Unit tests, Integration tests
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- Observation
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- Log
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- Metrics
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- Tracing
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In ZaloPay, each team has its own responsibilites/domains, aka many different
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services.
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Ideally each team can choose custom backend techstack if they want, but mostly
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boils down to Java or Go. Some teams use Python for scripting, data processing,
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...
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_Example_: UM (Team User Management Core) has 10+ Java services and 30+ Go
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services.
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The question is for each new business requirements, what should we do:
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- Create new services with new APIs?
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- Add new APIs to existing services?
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- Update existing APIs?
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- Change configs?
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- Don't do anything?
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_Example_: Business requirements says: Must match/compare user EKYC data with
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Bank data (name, dob, id, ...). TODO
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TODO: How to split services?
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## Technical side
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How do services communicate with each other?
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### API
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**First** is through API, this is the direct way, you send a request then you
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wait for response.
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**HTTP**: GET/POST/...
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_Example_: TODO use curl
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**GRPC**: use proto file as constract.
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_Example_: TODO: show sample proto file
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There are no hard rules on how to design APIs, only some best practices, like
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REST API, ...
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Correct answer will always be: "It depends". Depends on:
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- Your audience (android, ios, web client or another internal service)
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- Your purpose (allow to do what?)
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- Your current techstack (technology limitation?)
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- Your team (bias, prefer, ...?)
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- ...
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Why do we use HTTP for Client-Server and GRPC for Server-Server?
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- HTTP for Client-Server is pretty standard. Easy for client to debug, ...
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- Before ZaloPay switch to GRPC for Server-Server, we use HTTP. The reason for
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switch is mainly performance.
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#### References
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- [Best practices for REST API design](https://stackoverflow.blog/2020/03/02/best-practices-for-rest-api-design/)
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- [ZaloPay API](https://docs.zalopay.vn/v2/)
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- [stripe API](https://stripe.com/docs/api)
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- [moov API](https://docs.moov.io/api/)
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### Message Broker
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**Second** way is by Message Broker, the most well known is Kafka.
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Main idea is decoupling.
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Imaging service A need to call services B, C, D, E after doing some action, but
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B just died. We must handle B errors gracefully if B is not that important (not
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affect main flow of A). Imaging not only B, but multi B, like B1, B2, B3, ...
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Bn, this is so depressed to continue.
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Message Broker is a way to detach B from A.
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Dumb exaplain be like: each time A do something, A produces message to Message
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Broker, than A forgets about it. Then all B1, B2 can consume A's message if they
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want and do something with it, A does not know and does not need to know about
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it.
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#### References
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- [Using Apache Kafka to process 1 trillion inter-service messages](https://blog.cloudflare.com/using-apache-kafka-to-process-1-trillion-messages/)
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My own experiences:
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- Whatever you design, you stick with it consistently. Don't use different name
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for same object/value in your APIs.
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- Don't trust client blindly, everything can be fake, everything must be
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validated. We can not know the request is actually from our client or some
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hacker computer. (Actually we can but this is out of scope, and require lots
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of advance work)
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- Don't delete/rename/change old fields because you want and you can, please
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think it through before do it. Because back compability is very hard, old apps
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should continue to function if user don't upgrade. Even if we rollout new
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version, it takes time.
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**Pro tip**: Use proto to define models (if you can) to take advantage of
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detecting breaking changes.
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## Coding principle
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## Known concept
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TODO:
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## Challenge
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TODO: Scale problem
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## Damage control
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TODO: Take care incident
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## Bonus
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TODO
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## Draft
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single point of failure ownership, debugging
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