PWAs: the Application Shell & the well of surprises

When it comes to performance, we’ll usually take all the help we can get. The app shell model – an architecture for building PWAs – can make a huge difference… but better keep in mind it may hold a few surprises for you.

1. the Application Shell …and the well of surprises
2. Stratos Pavlakis Software guy @Blueground th3hunt
3. the Application Shell Why?
4. Web Performance a short primer
5. domContentLoaded navigationStart loadEventEnd time to first paint time to first paint time to interactive time to first byte frames per second page load time speed Index time to first ad first contentful paint first meaningful paint hero elements domainLookupStart
6. critical rendering path
7. Network Rendering
8. Request Page GET
 /page Network Rendering
9. Request Page Start building DOM wait GET
 /page Network Rendering HMTL
10. Request Page Start building DOM wait GET
 /page Network Rendering GET
 /style GET
 /js HMTL
11. Request Page Start building DOM Build CSSOM wait block GET
 /page Network Rendering GET
 /style GET
 /js CSS JS HMTL
12. Request Page Start building DOM Build CSSOM Run JS wait Continue DOM block GET
 /page Network Rendering GET
 /style GET
 /js CSS JS HMTL
13. Request Page Start building DOM Build CSSOM Run JS wait Continue DOM block style / layout / paint / comp GET
 /page Network Rendering GET
 /style GET
 /js CSS JS HMTL
14. Request Page Start building DOM Build CSSOM Run JS wait Continue DOM block styl GET
 /page Network Rendering GET
 /style GET
 /js CSS JS HMTL
15. Network Rendering
16. Network Rendering CPU / GPU
17. Network Rendering CPU / GPU Speed of Light
18. speed of light places a hard limit
 on the network latency!
19. imagine…
20. a single byte 1 1 0 1 1 0 1 0
21. in New York
22. distance light in vacuum light in fiber RTT London 5,585km 19ms 28ms 56ms Sydney 15,993km 53ms 80ms 160ms Thess 7,695km 26ms 38ms 76ms - Browser Networking, Ilya Grigorik Getting a byte from New York
23. 56 ms ?
24. you wish…
25. Client (London) Server (New York) TCP TLS
26. Client (London) Server (New York) 0 ms SYN 28 ms TCP TLS
27. Client (London) Server (New York) 0 ms SYN 28 ms SYN ACK ACK 56 ms TCP TLS
28. Client (London) Server (New York) 0 ms SYN 28 ms SYN ACK ACK 56 ms 140 ms ChangeCipherSpec
 Finished ClientHello 84 ms ClientKeyExchange
 ChangeCipherSpec 
 Finished
 ServerHello Cert
 ServerHelloDone
 112 ms 168 ms TCP TLS
29. Client (London) Server (New York) 0 ms SYN 28 ms SYN ACK ACK 56 ms Application 196 ms 140 ms ChangeCipherSpec
 Finished ClientHello 84 ms ClientKeyExchange
 ChangeCipherSpec 
 Finished
 ServerHello Cert
 ServerHelloDone
 112 ms 168 ms TCP TLS
30. Client (London) Server (New York) 0 ms SYN 28 ms SYN ACK ACK 56 ms Application 196 ms 140 ms ChangeCipherSpec
 Finished ClientHello 84 ms ClientKeyExchange
 ChangeCipherSpec 
 Finished
 ServerHello Cert
 ServerHelloDone
 112 ms 168 ms Application 224 ms TCP TLS
31. Client (London) Server (New York) 0 ms SYN 28 ms SYN ACK ACK 56 ms Application 196 ms 140 ms ChangeCipherSpec
 Finished ClientHello 84 ms ClientKeyExchange
 ChangeCipherSpec 
 Finished
 ServerHello Cert
 ServerHelloDone
 112 ms 168 ms Application 224 ms 11011010 TCP TLS
32. 224 ms
33. What if I send 1MB in 224ms?
34. well…
35. meet TCP Slow Start
36. Client (London) Server (New York) TCP Slow Start
37. Client (London) Server (New York) TCP Slow Start
38. Client (London) Server (New York) TCP Slow Start
39. Client (London) Server (New York) TCP Slow Start
40. Client (London) Server (New York) TCP Slow Start
41. 224ms + 2*56ms 3 * RTT for 64KB with init_cwnd = 10
42. “Even for small payloads network places a hard limit on speed”
43. Ok ok… but how bad can a few 100s of milliseconds be?
44. Delay User Perception 0 - 100ms Instant 100 - 300ms Perceptible delay 300 - 1000ms Machine is working 1000ms+ Likely mental context switch time and user perception Browser Networking - Ilya Grigorik
45. So… how do we deal with Mr. Network?
46. dealing with network latency
48. Edge Caching 1
49. 1 Edge Caching
50. 1 Edge Caching
51. Html Css Js Img Html Css Js Img Html Css Js Img Html Css Js Img Html Css Js Img 1 Edge Caching Html Css Js Img
52. Html Css Js Img Html Css Js Img Html Css Js Img Html Css Js Img Html Css Js Img 1 Edge Caching Html Css Js Img
53. Html Css Js Img Html Css Js Img Html Css Js Img Html Css Js Img Html Css Js Img 1 Edge Caching Html Css Js Img Static / JAMStack
55. HTTP2 Push 2
56. HTTP2 Push 2
57. HTTP2 Push 2 GET /index.html
58. HTTP2 Push 2 GET /index.html styles.css + app.js index.html
60. Service Workers 3
61. 3 Service Workers
62. 3 Service Workers
63. 3 Service Workers •Proxies of our own
64. 3 Service Workers •Proxies of our own •Live in the browser
65. 3 Service Workers •Proxies of our own •Live in the browser •Domain & path scoped
66. 3 Service Workers •Proxies of our own •Live in the browser •Domain & path scoped •Async by spec
67. 3 Service Workers •Proxies of our own •Live in the browser •Domain & path scoped •Async by spec •Utilize Cache API
68. 3 Service Workers •Proxies of our own •Live in the browser •Domain & path scoped •Async by spec •Utilize Cache API •Run on separate thread
69. the app shell
70. server browser
71. server browser cache
72. server browser GET /index.html cache
73. server browser index.html GET /index.html cache
74. service worker server browser cache
75. service worker server browser GET /index.html cache
76. service worker server browser GET /index.html index.html cache
77. service worker server browser GET /index.html index.html index.html cache
78. service worker server browser cache
79. service worker server browser GET /app.js, /style.css app.js, style.css cache
80. service worker server browser GET /app.js, /style.css app.js, style.css app.js style.js cache
81. service worker cache server browser
82. service worker cache server browser GET /index.html /style.css /app.js /logo.png /background.jpg
83. service worker cache server browser XHR XHR
84. Lifecycle
85. Lifecycle
86. Lifecycle
87. Lifecycle
88. Lifecycle pre-cache the shell (html, js, css, fonts)
89. Lifecycle pre-cache the shell (html, js, css, fonts) Cache runtime assets as they come (e.g. posted images)
91. Robert, a software engineer
92. Request Page Start building DOM Build CSSOM Run JS wait Continue DOM block style / layout / paint / comp GET
 /page GET
 /style GET
 /js css js html with a critical path to improve…
93. Improve the rendering Process? (Refactor code)
94. Improve the rendering Process? (Refactor code) That would involve…
95. Improve the rendering Process? (Refactor code) Designers That would involve…
96. Improve the rendering Process? (Refactor code) Developers Designers That would involve…
97. Improve the rendering Process? (Refactor code) Developers Designers That would involve… Product Owners
98. Better jump off a cliff
99. What about the network?
100. Edge Caching maybe?
101. Edge Caching maybe? DevOps Developers Test Engineers That would involve… Product Owners
102. HTTP2 Push?
103. HTTP2 Push? DevOps Developers Test Engineers That would involve…
104. What can service workers do?
105. What can service workers do? Cache stuff
106. What can service workers do? Cache stuff Even… cache the HTML document
107. What can service workers do? a few front end Devs That would only involve… Cache stuff Even… cache the HTML document
108. What can service workers do? a few front end Devs That would only involve… It would be just cross cut change that would eliminate the network Cache stuff Even… cache the HTML document
109. What can service workers do? a few front end Devs That would only involve… It would be just cross cut change that would eliminate the network once and for all !! Cache stuff Even… cache the HTML document
110. Perfecto…
111. let’s do it
112. the plan • Create a proof of concept • Deploy on staging • Work on the details while feedback is coming • Tweak a few things • Go Live!
113. the mentality • Go fast • Perform minimum changes • Involve as few as possible
114. proof of concept
115. <!-- Google Analytics --> <!-- Facebook Pixel —> SSR <html> SSR <script> /index.html PoC
116. SSR <html> SSR <script> Tag Manager /index.html PoC
117. SSR <html> SSR <script> Tag Manager /index.html PoC
118. Tag Manager /index.html PoC
119. /index.html PoC
120. /index.html but that is slower for older browsers that don’t support SWs PoC
121. /index.html PoC
122. /index.html Browser: /index.html Worker: /index-shell.html PoC
123. more Developers involved
124. sw.js var cacheFiles = [ “./index-shell.html”, "./js/app.js", "./css/style.css" ]; self.addEventListener("install", e "=> { e.waitUntil( caches.open(cacheName).then(cache "=> { return cache.addAll(cacheFiles); }) ); });
125. "./js/app.js", "./css/style.css" ]; self.addEventListener("install", e "=> { e.waitUntil( caches.open(cacheName).then(cache "=> { return cache.addAll(cacheFiles); }) ); }); self.addEventListener("fetch", function(e) { if (e.request.url.match(/\/index.html/)) { e.respondWith(caches.match('/index-shell.html')); } });
126. navigator.serviceWorker .register(“/sw.js”, { scope: "./" }) .then(() "=> { console.log(“[ServiceWorker] Registered"); }) .catch(err "=> { console.log(“[ServiceWorker] Failed to Register", err); }); index.html
127. to staging!
129. …from staging
130. Surprise #1 /index.html Cannot submit any form
131. Surprise #1 /index.html
132. Surprise #1 /index.html <meta name=“csrf-token” content=“…” />
133. Surprise #1 /index.html Keep CSRF token in a
134. all Developers involved
135. to staging!
137. …from staging
138. Surprise #2 /index.html CSS is not loading
139. Surprise #2 /index.html
140. Surprise #2 /index.html meet Opaque responses
141. Surprise #2 /index.html meet Opaque responses
142. Surprise #2 /index.html meet Opaque responses • Responses to requests made to a remote origin 
 when CORS is not enabled
143. Surprise #2 /index.html meet Opaque responses • Responses to requests made to a remote origin 
 when CORS is not enabled • status == 0
144. Surprise #2 /index.html meet Opaque responses • Responses to requests made to a remote origin 
 when CORS is not enabled • status == 0 • no access to headers
145. Surprise #2 /index.html meet Opaque responses • Responses to requests made to a remote origin 
 when CORS is not enabled • status == 0 • no access to headers • no access to body
146. Surprise #2 /index.html meet Opaque responses • Responses to requests made to a remote origin 
 when CORS is not enabled • status == 0 • no access to headers • no access to body • Using a CDN? => your assets on a remote origin
147. Surprise #2 /index.html meet Opaque responses const request = new Request( 'https:"//no-cors-cdn.com/style.css', { mode: 'no-cors' } ); fetch(request).then(response "=> cache.put(request, response) );
148. Surprise #2 /index.html meet Opaque responses Configure CORS for all your cached assets <link crossorigin=‘anonymous’ /> Your JS should already be so for error monitoring
149. DevOps involved
150. to staging!
151. no news,
 maybe it’s time for those details…
152. Detail #1 /index.html App has been updated. Click here to reload •When? •Won’t it become annoying? •Backwards compatibility?
153. That is a BIG FAT detail, right there!
154. Detail #1 /index.html App has been updated. Click here to reload Treat your web app as a mobile app
155. Detail #1 /index.html App has been updated. Click here to reload •Set ShellVersion in index.html •Add ShellVersion HTTP Header 
 to all XHR requests •Bump it on every release/deploy
 based on watched files
156. Detail #1 /index.html App has been updated. Click here to reload •Set minimum supported version •Return client error HTTP status 
 (e.g. 430) if below minimum
157. Detail #1 /index.html App has been updated. Click here to reload Show update prompt up to 2 times/ day for + on 430s.
158. PMs definitely involved
160. …from staging
161. Surprise #3 /index.html Safari not working - at all
162. Detail #2 /index.html How to unregister a buggy 
 service worker?
163. Detail #2 /index.html Be prepared! No deployment should be required
164. Detail #2 /index.html no big deal bug? ENV.SW_TYPE=“NOOP” self.addEventListener('install', function () { self.skipWaiting(); console.log('NOOP service worker installed'); }); self.addEventListener('activate', function (event) { event.waitUntil(clients.claim()); console.log('NOOP service worker activated'); });
165. Detail #2 /index.html HUGE deal bug? ENV.SW_TYPE=“DESTROYER” self.addEventListener('install', function (e) { self.skipWaiting(); }); self.addEventListener('activate', function (e) { self.registration.unregister() .then(function () { return self.clients.matchAll(); }) .then(function (clients) { clients.forEach(client "=> client.navigate(client.url)); });
166. Detail #2 /index.html /purge-caches •Caches •Storage •IDB •Service Workers Clear-Site HTTP Header (W3C working draft)
167. DevOps involved. Again.
168. to staging!
170. …from staging
171. Surprise #3 /index.html it’s not thaaaat fast…
172. What did you just say to me!??
173. Surprise #3 /index.html We removed SSR. To go beyond user perceived performance and ACTUALLY load faster, you need to approach the idea of… offline first
174. Surprise #3 /index.html Offline first (simple case) Serve cached content from IDB or localStorage, while fetching fresh data from the server.
175. authenticated users == user specific content
176. Surprise #3 /index.html 1.Sign in as Bob 2.Sign out 3.Sign in as Alice 4.What does Alice see? caching the user specific content, poses this problem
177. Surprise #3 /index.html clear all caches on /signout?
178. Surprise #3 /index.html clear all caches on /signout? won’t work :(
179. Surprise #3 /index.html clear all caches on /signin?
180. Surprise #3 /index.html clear all caches on /signin? won’t work :(
181. need to create a personal service worker
182. Surprise #3 /index.html /app_shell /index.html?uid=4w321r /signin
183. Surprise #3 /index.html /app_shell /index.html?uid=4w321r /signin match with UID
184. Surprise #3 /index.html /app_shell /index.html?uid=4w321r /signin + Scope IDB, Storage keys under this UID e.g. “/uid/42321/avatarUrl” match with UID
185. self.addEventListener("fetch", function(e) { if (e.request.url.match(/\/index.html?uid=4w221r/)) { e.respondWith(caches.match('/index-shell.html')); } });
187. Offline first… would involve EVERYONE
188. epilogue
189. Robert case takeaways
190. PWAs should be treated as… Apps
191. PWAs will remind you…
192. Cache invalidation is a hard thing :P
193. Great performance is
 a team thing!
194. Thank you! Questions? Stratos Pavlakis Software guy @Blueground th3hunt