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<h2>
<a href="index.html"><code>~</code></a>
</h2>
<h1>
<a
id="user-content-backend-thinking"
class="anchor"
aria-hidden="true"
tabindex="-1"
href="#backend-thinking"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Backend Thinking
</h1>
<h2>
<a
id="user-content-backend-role"
class="anchor"
aria-hidden="true"
tabindex="-1"
href="#backend-role"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Backend Role
</h2>
<p>Transform business requirements to action, which usually involves:</p>
<ul>
<li>
Service:
<ul>
<li>
ZaloPay use microservices architecture, mostly written using Go and
Java
</li>
</ul>
</li>
<li>
API:
<ul>
<li>HTTP (Client-Server) and GRPC (Server-Server)</li>
</ul>
</li>
<li>
Database/Cache/Storage/Message Broker
<ul>
<li>MySQL/Redis/S3/Kafka</li>
<li>CRUD</li>
</ul>
</li>
<li>
Docs
<ul>
<li>
Mostly design notes and diagrams which show how to implement
business requirements
</li>
</ul>
</li>
</ul>
<p>After successfully do all of that, next step is:</p>
<ul>
<li>
Testing
<ul>
<li>Unit tests, Integration tests</li>
</ul>
</li>
<li>
Observation
<ul>
<li>Log</li>
<li>Metrics</li>
<li>Tracing</li>
</ul>
</li>
</ul>
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<p>
In ZaloPay, each team has its own responsibilites/domains, aka many
different services.
</p>
<p>
Ideally each team can choose custom backend techstack if they want, but
mostly boils down to Java or Go. Some teams use Python for scripting, data
processing, ...
</p>
<p>
<em>Example</em>: UM (Team User Management Core) has 10+ Java services and
30+ Go services.
</p>
<p>
The question is for each new business requirements, what should we do:
</p>
<ul>
<li>Create new services with new APIs?</li>
<li>Add new APIs to existing services?</li>
<li>Update existing APIs?</li>
<li>Change configs?</li>
<li>Don't do anything?</li>
</ul>
<p>
<em>Example</em>: Business requirements says: Must match/compare user EKYC
data with Bank data (name, dob, id, ...). TODO
</p>
<p>TODO: How to split services?</p>
<h2>
<a
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id="user-content-technical-side"
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class="anchor"
aria-hidden="true"
tabindex="-1"
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href="#technical-side"
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><span aria-hidden="true" class="octicon octicon-link"></span></a
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>Technical side
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</h2>
<p>How do services communicate with each other?</p>
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<h3>
<a
id="user-content-api"
class="anchor"
aria-hidden="true"
tabindex="-1"
href="#api"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>API
</h3>
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<p>
<strong>First</strong> is through API, this is the direct way, you send a
request then you wait for response.
</p>
<p><strong>HTTP</strong>: GET/POST/...</p>
<p><em>Example</em>: TODO use curl</p>
<p><strong>GRPC</strong>: use proto file as constract.</p>
<p><em>Example</em>: TODO: show sample proto file</p>
<p>
There are no hard rules on how to design APIs, only some best practices,
like REST API, ...
</p>
<p>Correct answer will always be: "It depends". Depends on:</p>
<ul>
<li>
Your audience (android, ios, web client or another internal service)
</li>
<li>Your purpose (allow to do what?)</li>
<li>Your current techstack (technology limitation?)</li>
<li>Your team (bias, prefer, ...?)</li>
<li>...</li>
</ul>
<p>Why do we use HTTP for Client-Server and GRPC for Server-Server?</p>
<ul>
<li>
HTTP for Client-Server is pretty standard. Easy for client to debug, ...
</li>
<li>
Before ZaloPay switch to GRPC for Server-Server, we use HTTP. The reason
for switch is mainly performance.
</li>
</ul>
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<h4>
<a
id="user-content-references"
class="anchor"
aria-hidden="true"
tabindex="-1"
href="#references"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>References
</h4>
<h3>
<a
id="user-content-message-broker"
class="anchor"
aria-hidden="true"
tabindex="-1"
href="#message-broker"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Message Broker
</h3>
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<p>
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<strong>Second</strong> way is by Message Broker, the most well known is
Kafka.
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</p>
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<p>Main idea is decoupling.</p>
<p>
Imaging service A need to call services B, C, D, E after doing some
action, but B just died. We must handle B errors gracefully if B is not
that important (not affect main flow of A). Imaging not only B, but multi
B, like B1, B2, B3, ... Bn, this is so depressed to continue.
</p>
<p>Message Broker is a way to detach B from A.</p>
<p>
Dumb exaplain be like: each time A do something, A produces message to
Message Broker, than A forgets about it. Then all B1, B2 can consume A's
message if they want and do something with it, A does not know and does
not need to know about it.
</p>
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<h3>
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<a
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id="user-content-tip"
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class="anchor"
aria-hidden="true"
tabindex="-1"
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href="#tip"
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><span aria-hidden="true" class="octicon octicon-link"></span></a
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>Tip
</h3>
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<ul>
<li>
Whatever you design, you stick with it consistently. Don't use different
name for same object/value in your APIs.
</li>
<li>
Don't trust client blindly, everything can be fake, everything must be
validated. We can not know the request is actually from our client or
some hacker computer. (Actually we can but this is out of scope, and
require lots of advance work)
</li>
<li>
Don't delete/rename/change old fields because you want and you can,
please think it through before do it. Because back compability is very
hard, old apps should continue to function if user don't upgrade. Even
if we rollout new version, it takes time.
</li>
</ul>
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<p>
<strong>Pro tip</strong>: Use proto to define models (if you can) to take
advantage of detecting breaking changes.
</p>
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<h3>
<a
id="user-content-references-1"
class="anchor"
aria-hidden="true"
tabindex="-1"
href="#references-1"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>References
</h3>
<ul>
<li>
<a
href="https://stackoverflow.blog/2020/03/02/best-practices-for-rest-api-design/"
rel="nofollow"
>Best practices for REST API design</a
>
<ul>
<li>
<a href="https://docs.zalopay.vn/v2/" rel="nofollow">ZaloPay API</a>
</li>
<li>
<a href="https://stripe.com/docs/api" rel="nofollow">stripe API</a>
</li>
<li>
<a href="https://docs.moov.io/api/" rel="nofollow">moov API</a>
</li>
</ul>
</li>
<li>
<a
href="https://blog.cloudflare.com/using-apache-kafka-to-process-1-trillion-messages/"
rel="nofollow"
>Using Apache Kafka to process 1 trillion inter-service messages</a
>
</li>
</ul>
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<h2>
<a
id="user-content-coding-principle"
class="anchor"
aria-hidden="true"
tabindex="-1"
href="#coding-principle"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Coding principle
</h2>
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<p>
You should know about DRY, SOLID, KISS, Design Pattern. The basic is
learning which is which when you read code. Truly understand will be
knowing when to use and when to not.
</p>
<p>All of these above are industry standard.</p>
<p>
The way business moving is fast, so a feature is maybe implemented today,
but gets thrown out of window tomorrow (Like A/B testing, one of them is
chosen, the other says bye). So how do we adapt? The problem is to detect,
which code/function is likely stable, resisted changing and which is
likely to change.
</p>
<p>
For each service, I often split to 3 layers: handler, service, repository.
</p>
<ul>
<li>Handler layer: Handle HTTP/GRPC/Message Broker/...</li>
<li>Service layer: All rules, logic goes here.</li>
<li>
Repository layer: Interact with cache/databases using CRUD and some
cache strategy.
</li>
</ul>
<p>
Handler layer is likely never changed. Repository layer is rarely changed.
Service layer is changed daily, this is where I put so much time on.
</p>
<p>The previous question can be asked in many ways:</p>
<ul>
<li>How to move fast without breaking things?</li>
<li>How to quickly experiment new code without affecting old code?</li>
<li>...</li>
</ul>
<p>
My answer is, as Message Broker introduce concept decoupling, loosely
coupled coding. Which means, 2 functions which do not share same business
can be deleted without breaking the other.
</p>
<p>
For example, we can send noti to users using SMS, Zalo, or Noti in app (3
providers). They are all independently feature which serves same purpose:
alert user about something. What happen if we add providers or remove
some? Existing providers keep working as usual, new providers should
behave properly too.
</p>
<p>
So we have send noti abstraction, which can be implement by each provider,
treat like a module (think like lego) which can be plug and play right
away.
</p>
<p>
And when we do not need send noti anymore, we can delete whole of it which
includes all providers and still not affecting main flow.
</p>
<h3>
<a
id="user-content-references-2"
class="anchor"
aria-hidden="true"
tabindex="-1"
href="#references-2"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>References
</h3>
<ul>
<li>
<a
href="https://programmingisterrible.com/post/139222674273/write-code-that-is-easy-to-delete-not-easy-to"
rel="nofollow"
>Write code that is easy to delete, not easy to extend.</a
>
</li>
<li>
<a
href="https://cerebralab.com/Imaginary_Problems_Are_the_Root_of_Bad_Software"
rel="nofollow"
>Imaginary Problems Are the Root of Bad Software</a
>
</li>
</ul>
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<h2>
<a
id="user-content-known-concept"
class="anchor"
aria-hidden="true"
tabindex="-1"
href="#known-concept"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Known concept
</h2>
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<p>TODO: Cache strategy, async operation</p>
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<h2>
<a
id="user-content-challenge"
class="anchor"
aria-hidden="true"
tabindex="-1"
href="#challenge"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Challenge
</h2>
<p>TODO: Scale problem</p>
<h2>
<a
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id="user-content-damage-control"
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class="anchor"
aria-hidden="true"
tabindex="-1"
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href="#damage-control"
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><span aria-hidden="true" class="octicon octicon-link"></span></a
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>Damage control
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</h2>
<p>TODO: Take care incident</p>
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<h2>
<a
id="user-content-bonus"
class="anchor"
aria-hidden="true"
tabindex="-1"
href="#bonus"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Bonus
</h2>
<p>TODO</p>
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