How can we develop websites where the different parts of the pages are developed by different teams? If you work in a large enough organization which has its content and services on the web, this is probably a question you have asked yourself several times. With this talk I want to show that server-side rendered websites integrated on content (using transclusion) allow for high long-term evolvability compared to client-side rendering integrated with shared code. In other words, if you want a system with high long-term evolvability, you should not develop websites using only client-side JavaScript and integrate them using a shared components approach.

1. MICROSERVICE
WEBSITES
Gustaf Nilsson Kotte
@gustaf_nk

2. Mobile devices
The problem

3. How can we develop a website with multiple teams?
Different business units need to make a website together
that should feel like “one website” for the end-user.
Example: Retail domain
Products, Shopping cart, Checkout, Recommendations, Reviews,
User profile, Editorial content, etc...
The problem

4. Decentralized services but centralized web?
Frontend
Bottleneck

5. Services should have their own frontend!
Stefan Tilkov et al, “Self-Contained Systems”
Frontend Frontend FrontendFrontend
Autonomy → Continuous delivery

6. Decentralized governance
An option for teams to choose different tools
→ heterogeneous/plural/diverse system
High rate of change on the frontend
Allows the system to evolve over time
James Lewis & Martin Fowler, “Microservices: Decentralized Governance”

7. Addy Osmani, “JavaScript Start-up Performance”
Mobile device performance

8. Constraints (need to support)
Continuous delivery
Decentralized governance
Good performance on mobile devices
Microservice Websites

9. Mobile devices
Analysis

10. INTEGRATION USE CASE
Shopping cart
How can we reuse the shopping cart between
different parts of the web site?
“Many-to-one”
Multiple teams – one shopping cart

11. INTEGRATION USE CASE
Landing page
The web site’s landing page is the page with the
most amount of traffic and many business units
want to be represented there.
“One-to-many”
Multiple teams – one landing page

12. Integrating on...
What (data/code/content)
When (build/run)
Where (client/server)
Cartesian product → 12 combinations
Let’s go through them!
Analysis

13. What × when × where
What? When? Where?
Data (APIs) Build Client
Server
Run Client
Server
Code (JavaScript, PHP, etc) Build Client
Server
Run Client
Server
Content (HTML) Build Client
Server
Run Client
Server
What × when × where

14. What × when × where
What? When? Where?
Data (APIs) Build Client No reuse at all, only API usage
Server
Run Client
Server
Code (JavaScript, PHP, etc) Build Client
Server
Run Client
Server
Content (HTML) Build Client
Server
Run Client
Server
What × when × where

15. What × when × where
What? When? Where?
Data (APIs) Build Client No reuse at all, only API usage
Server
Run Client
Server
Code (JavaScript, PHP, etc) Build Client No continuous delivery. No diversity + mobile performance.
Server
Run Client
Server
Content (HTML) Build Client
Server
Run Client
Server
What × when × where

16. What × when × where
What? When? Where?
Data (APIs) Build Client No reuse at all, only API usage
Server
Run Client
Server
Code (JavaScript, PHP, etc) Build Client No continuous delivery. No diversity + mobile performance.
Server
Run Client No diversity + mobile performance.
Server N/A
Content (HTML) Build Client
Server
Run Client
Server
What × when × where

17. What × when × where
What? When? Where?
Data (APIs) Build Client No reuse at all, only API usage
Server
Run Client
Server
Code (JavaScript, PHP, etc) Build Client No continuous delivery. No diversity + mobile performance.
Server
Run Client No diversity + mobile performance.
Server N/A
Content (HTML) Build Client
Server
Run Client
Server
What × when × where

18. What × when × where
What? When? Where?
Data (APIs) Build Client No reuse at all, only API usage
Server
Run Client
Server
Code (JavaScript, PHP, etc) Build Client No continuous delivery. No diversity + mobile performance
Server
Run Client No diversity + mobile performance.
Server N/A
Content (HTML) Build Client N/A
Server “Static page fragments” – ok, but limited amount of use cases
Run Client
Server
What × when × where

19. What × when × where
What? When? Where?
Data (APIs) Build Client No reuse at all, only API usage
Server
Run Client
Server
Code (JavaScript, PHP, etc) Build Client No continuous delivery. No diversity + mobile performance.
Server
Run Client No diversity + mobile performance.
Server N/A
Content (HTML) Build Client N/A
Server “Static page fragments” – ok, but limited amount of use cases
Run Client Client-side transclusion
Server Server-side transclusion
What × when × where

20. What? When? Where?
Data (APIs) Build Client No reuse at all, only API usage
Server
Run Client
Server
Code (JavaScript, PHP, etc) Build Client No continuous delivery. No diversity + mobile performance.
Server
Run Client No diversity + mobile performance.
Server N/A
Content (HTML) Build Client N/A
Server “Static page fragments” – ok, but limited amount of use cases
Run Client Client-side transclusion
Server Server-side transclusion
What × when × whereWhat × when × where

21. Mobile devices
Transclusion

22. Transclusion
“transclusion is the inclusion of part or all of an electronic document
into one or more other documents by hypertext reference” (Wikipedia: Transclusion)
Producer
Expose a fragment resource, "/retail/shopping-cart/"
Consumer
Include the fragment declaratively, similar to <img src="..." />
Transclusion can be used both on server and client
Examples: Edge-Side Includes (server) and <h-include> (client)

23. Edge Side Includes (server)
<-- Include the shopping cart component -->
<esi:include src="/retail/shopping-cart/" />
ESI 1.0 proposal submitted to W3C 2001
CDN support: Akamai, Fastly
On-premise support: Varnish, Squid, nodesi, etc

24. <h-include> (client)
<h-include src="/retail/shopping-cart/"></h-include>
Custom Elements version of hinclude.js (by Mark Nottingham, 2006)
Difference: interface and transitive includes
HTTP/2 → Bundles multiple xhr requests into one
Both support refresh()

25. ESI (server)
+ SEO
+ JS/CSS in responses works as usual
+ Initial performance
+ Cross-domain requests
- Extra infrastructure investment
- Dev perspective (+ i.e. nodesi)
- No streamed responses ⇒ blocking
- Performance sensitive (+ timeouts)
- No header forwarding (+ configuration)
Server transclusion vs client transclusion
h-include (client)
- No SEO
- No loading of JS/CSS in responses
- Delay before xhr requests arrive
- No cross-domain requests (unless CORS)
- If no initial width/height, page will “jump”
+ No extra infrastructure investment
+ No extra dev setup
+ Async ⇒ non-blocking
+ Responses are rendered when they arrive
+ Headers work as usual in browsers

26. ESI and h-include together (1)
// Refresh-only h-include
var proto = Object.create(HIncludeElement.prototype);
proto.attachedCallback = function() { /* do nothing */ };
document.registerElement('h-include-refresh-only', {
prototype: proto,
});
⇒ <h-include-refresh-only src="...">REFRESHABLE CONTENT HERE</h-include-refresh-only>
Allows us to wrap the ESI fragment response in an h-include-refresh-only
⇒ server-side initial content with client-side refreshes

27. ESI and h-include together (2)
// Lazy-loading with hunt.js
window.addEventListener('load', function() {
// For these elements...
hunt(document.getElementsByTagName('h-include-refresh-only'), {
// ...when they’re almost in the viewport...
offset: 400,
// ...load them!
in: function() {
this.refresh();
},
});
});

28. Constraints (need to support)
Continuous delivery
Decentralized governance
Good performance on mobile devices
Rules for integration
Transclude server-side resources
Microservice Websites

29. Mobile devices
Client-side
dependencies

30. Shopping cart HTML, check!
But, what about...
Additional client-side behavior? (JavaScript)
Design? (CSS)

31. How to import service dependencies
Still need cache busting (i.e. /retail/shopping-cart/scripts-aef419.js)
Server-side transclusion works well here
Client-side transclusion require either 1) HTTP redirects, or 2) “loaders” like little-loader for JS and loadCSS
for CSS. Both options are less performant than using server-side transclusion, because of extra client/server
roundtrips.

32. <head>
...
<!-- Include shopping cart resources (cache-busting-as-a-service) -->
<esi:include src="/retail/shopping-cart/stylesheets/" />
...
</head>
<body>
...
<-- Include the shopping cart component -->
<esi:include src="/retail/shopping-cart/" />
…
<esi:include src="/retail/shopping-cart/scripts/" />
</body>
Load dependencies (before transclusion)

33. <head>
...
<!-- Include shopping cart resources (cache-busting-as-a-service) -->
<link rel="stylesheet" src="/retail/shopping-cart/style-ffc864.css" />
...
</head>
<body>
...
<-- Include the shopping cart component -->
<div class="shopping-cart">Hello, shopping cart</div>
...
<script src="/retail/shopping-cart/scripts-aef419.js"></script>
</body>
Load dependencies (after transclusion)

34. Client-side dependencies: JavaScript
No assumptions of consuming services’ client-side dependencies
⇒ Vanilla JS + polyfills (neither are “free”, so use both with care)
Custom Elements simplifies the lifecycle of components
https://github.com/WebReflection/document-register-element (5 KB)

35. Client-side dependencies: CSS
Disclaimer: I’m not a CSS expert
Large-scale CSS development is hard (but what’s the alternative?)
Styleguide
Namespacing/components/responsive/flexible
Good news: others have this problem too (i.e. “multi-team SPAs”)
Small global dependency for resets and typography (optional)

36. Constraints (need to support)
Continuous delivery
Decentralized governance
Good performance on mobile devices
Rules for integration
Transclude server-side resources
No global client-side dependencies
Microservice Websites

37. Mobile devices
Summary

38. Services should have their own frontend!
Frontend Frontend FrontendFrontend
Integration: Transclusion

39. Constraints (need to support)
Continuous delivery
Decentralized governance (otherwise: “occasional” rewrites)
Good performance on mobile devices
Rules for integration (free to use JS frameworks internally, but not for exported fragments)
Transclude server-side resources
No global client-side dependencies
Microservice Websites

40. Further resources
Microservice Websites, Gustaf Nilsson Kotte
Microservices, James Lewis & Martin Fowler
Self-Contained Systems, Stefan Tilkov et al.
Architecture Without an End State, Michael Nygard
JavaScript Start-up Performance, Addi Osmani
Also, this is a great book:
I’ll happily chat on twitter: @gustaf_nk