Revisiting HTTP/2
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RFC 7540 was ratified over 2 years ago and, today, all major browsers, servers, and CDNs support the next generation of HTTP. Just over a year ago, at Velocity, we discussed the protocol, looked at some real world implications of its deployment and use, and what realistic expectations we should have from its use. Now that adoption is ramped up and the protocol is being regularly used on the Internet, it's a good time to revisit the protocol and its deployment. Has it evolved? Have we learned anything? Are all the features providing the benefits we were expecting? What's next?In this session, we'll review protocol basics and try to answer some of these questions based on real-world use of it. We'll dig into the core features like interaction with TCP, server push, priorities and dependencies, and HPACK. We'll look at these features through the lens of experience and see if good practice patterns have emerged. We'll also review available tools and discuss what protocol enhancements are in the near and not-so-near horizon.
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Revisiting HTTP/2
- 2. Yes, I like being interviewed, but I’m tired of hearing this guy talk about HTTP/2
- 6. connection
- 7. connection • A single, long lasting connection • Theoretically, this means better congestion management between peers • TLS/ALPN
- 8. connection stream stream stream … frame frame frame frame frame frame frame frame frame frame frame frame frame frame frame frame frame frame frame
- 9. DATA Carries request or response data HEADERS Carries request/response headers/trailers; can initiate a stream PRIORITY Indicates priority of a stream RST_STREAM Terminates a stream SETTINGS Defines parameters for the connection only PUSH_PROMISE Signals peer for server push PING Maintenance frame for checking RTT, connection, etc GOAWAY For shutting down a connection WINDOW_UPDATE Frame responsible for flow control adjustments CONTINUATION Extends a HEADERS frame and can carry more headers
- 10. GET /thing HTTP/1.1 Host: www.example.com User-Agent: Some_user_agent HTTP/1.1 200 OK Server: some_server Content-Type: text/html Content-Length: 1000 html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html Request Response
- 11. GET /thing HTTP/1.1 Host: www.example.com User-Agent: Some_user_agent HTTP/1.1 200 OK Server: some_server Content-Type: text/html Content-Length: 1000 html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html html DATA DATA DATA DATA DATA DATA HEADERS Request Response HEADERS
- 12. HTTP/2 Frame TCP TLS TLS Record HTTP/2 Frame HTTP/2 Frame … Stream ID Stream ID Stream ID TCP TLS TLS Record Header: valuern Header: valuern Header: valuern rn Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body HTTP/1 HTTP/2
- 13. Protocol flow
- 16. HTTP/1 response connection request Head-of-line blocking: nothing else can happen over the connection while busy with request/response
- 17. HTTP/1 response connection request response connection request response connection request response connection request response connection request
- 21. HTTP/1.1 HTTP/2
- 26. HTTP/2
- 27. HTTP/2 & TCP
- 30. PLR
- 31. 0% PLR 0.5% PLR 1% PLR 2% PLR
- 32. 0% PLR 2% PLR 5Mbps/1Mbps 40ms 780Kbps/330Kbps 200ms 5Mbps/1Mbps 40ms 780Kbps/330Kbps 200ms Doc Complete h2 h2 h2 h2 h1 h1 h1 h1 DCL Start h1 h1 h2 h1 h1 h1 h2 h1 Speed Index h2/h1 h2 h2 h2 h1 h1 h2 h2
- 33. 0% PLR 2% PLR 5Mbps/1Mbps; 40ms 780Kbps/330Kbps; 200ms 5Mbps/1Mbps; 40ms 780Kbps/330Kbps; 200ms Site1a (Fastly) DocComplete h2 h2 h2 h1 h1 h1 h1 h1 DCL Start h2 h1 h2 h2 h2/h1 h1 h2 h2 Speed Index h1 h2 h2 h2 h1 h2/h1 h2/h1 h2 Site1b DocComplete h2/h1 h2 h2 h2 h1 h2 h1 h2/h1 DCL Start h1 h2 h1 h1 h1 h2/h1 h1 h1 Speed Index h1 h2 h2 h1 h1 h2/h1 h1 h1 Site1c DocComplete h1/h2 h2 h2 h2 h1 h1 h1 h1 DCL Start h1 h1/h2 h1 h1 h1 h2 h1 h1 Speed Index h2 h2 h1 h2 h1 h2 h1 h1 Site2a DocComplete h2 h2 h2 h2 h1 h2/h1 h1 h1 DCL Start h2 h2 h2 h2 h1 h1 h1 h1 Speed Index h1 h2 h1 h2 h1 h2 h1 h2 Site2b DocComplete h2 h2 h2 h2 h1 h1/h2 h1 h1 DCL Start h2 h2 h1 h2 h1 h2 h1 h2 Speed Index h2 h1/h2 h1 h1/h2 h2 h2 h1 h1 Site3a DocComplete h2 h2 h1 h2 h2 h2 h1 h1 DCL Start h2 h2 h2 h2 h2 h2 h2 h2 Speed Index h2 h2 h1 h1 h1/h2 h1/h2 h1 h1 Site3b DocComplete h2 h2 h2 h1/h2 h2 h2/h1 h2 h2 DCL Start h2 h2 h2 h2 h2 h2 h2 h2 Speed Index h1 h2 h1 h1 h1 h2 h1 h1 Site3c DocComplete h1 h2 h2 h2 h1 h2 h2 h2 DCL Start h1/h2 h2 h1 h1/h2 h2/h1 h2 h1 h2/h1 Speed Index h1 h2 h2 h2 h2 h2 h2 h2
- 34. Why?
- 39. Head of line blocking in TCP
- 41. I really wish there were some academic papers on this…
- 42. Some reading… • http://c3lab.poliba.it/images/3/3b/QUIC_SAC15.pdf • https://www.usenix.org/system/files/conference/nsdi14/nsdi14-paper- wang_xiao_sophia.pdf • http://arxiv.org/pdf/1507.06562v1.pdf • http://nl.cs.montana.edu/lab/publications/Goel_H2_extended.pdf • https://99designs.com.au/tech-blog/blog/2016/07/14/real-world-http-2-400gb-of- images-per-day/
- 43. Takeaways (then) • Despite the experiment flaws, performance benefits are less than clear cut, out of the box • Seemed best: - Not listen to anyone! - Try for yourself
- 45. BBR
- 48. Bountifully Beneficial Reading • https://github.com/google/bbr/blob/master/Presentations/ bbr-2017-02-08-google-net-research-summit.pdf • https://www.ietf.org/proceedings/97/slides/slides-97-iccrg- bbr-congestion-control-02.pdf • https://github.com/google/bbr • https://dl.acm.org/citation.cfm?id=3009824 • https://arxiv.org/pdf/1706.09115.pdf
- 51. https://blogs.dropbox.com/tech/2017/09/optimizing-web-servers-for-high-throughput-and-low-latency/
- 52. BBR things… • Is BBR a good network citizen? • “network waterboarding” • There’s still work to do
- 59. Origin frame • List of domains eligible for coalescing - Cert still needs to match • Empty frame signals no coalescing - Fall back to SNI • Obviates DNS lookups for listed domains
- 60. Origin frame • List of domains eligible for coalescing - Cert still needs to match • Empty frame signals no coalescing - Fall back to SNI • Obviates DNS lookups for listed domains
- 61. Origin frame • List of domains eligible for coalescing - Cert still needs to match • Empty frame signals no coalescing - Fall back to SNI • Obviates DNS lookups for listed domains
- 62. The connection is an authoritative and secure context
- 63. The connection is an authoritative and secure context
- 64. The connection is an authoritative and secure context
- 65. h2 and TCP • Performance benefits? - Anecdotal, seems to vary from case to case - BBR helps, but pros/cons aren’t totally clear yet - It’s still best to figure out what’s best for you on your own! • We’re about to get more control over some coalescing • The context of a connection is being relied on more and more
- 67. Push basic • “push” a resource to the client before it’s requested • Only servers can push • Triggered by PUSH_PROMISE frame
- 68. connection
- 69. connection
- 70. connection
- 71. What to push? • A replacement for inlining - All the RTT-saving benefits + caching • Google paper: - https://docs.google.com/a/fastly.com/drawings/d/ 1mWwY_MeNAjzDRCF0uT97KgN0lh_jX79a53X6iOuH_Is/pub? w=2330&h=1350 • Facebook: - https://www.facebook.com/atscaleevents/videos/1775942979345465/
- 72. Link: </css1.css>; rel=preload; as=style https://w3c.github.io/preload/
- 73. Benefits?
- 80. “Async” Push
- 82. Push with Link header Async Push
- 83. of course it isn’t that simple…
- 84. The client cache
- 85. RST_STREAM
- 86. RST_STREAM
- 90. +-------------------------------+-------------------------------+ | Origin-Len (16) | Origin? (*) ... +-------------------------------+-------------------------------+ | Digest-Value? (*) ... +---------------------------------------------------------------+
- 91. We still have work to do... It shouldn’t be this difficult!
- 93. Adoption? • 0.04% of HTTP/2 sessions have a push frame • Average amount of pushed data per session: 32KB • Success rate: • 63.51% accepted • 22.35% time out • 13.39% duplicate https://github.com/httpwg/wg-materials/blob/gh-pages/ietf102/chrome_push.pdf
- 95. 103
- 99. Fetch stuff!!
- 101. { 103
- 102. Pushing for push • Is the 1RTT worth the complexity? • 103 to the browser: - Same benefit as push for the most important use-case - Much simpler - Leverage browser cache • “To push or not to push” by Patrick Hamann - https://www.youtube.com/watch?v=cznVISavm-k • Cache digests may still be useful? • What do we do with push?
- 103. Prioritization Priority #1: skiing h2 priority? h2 schmriority
- 104. Prioritization basics • Address possible contention because of all the concurrency • Stream weights • Dependency (including exclusivity) • HEADERS and PRIORITY frames • It’s only a “suggestion”
- 105. Example • D gets all resources • After D is done: - C gets ½ of resources - E gets ½ of resources • After C is done: - A gets ¾ of C’s ½ of resources - B gets ¼ of C’s ½ of resources * D 1 C 8 A 12 B 4 E 8
- 115. Priority hints
- 117. Tools and resources
- 119. Browser indicator • Chrome: – https://chrome.google.com/webstore/detail/http2-and-spdy- indicator/mpbpobfflnpcgagjijhmgnchggcjblin?hl=en • Firefox: – https://addons.mozilla.org/en-US/firefox/addon/http2-indicator/
- 120. Dev tools
- 121. Wireshark Using the TLS key file: https://jimshaver.net/2015/02/11/decrypting-tls-browser-traffic-with-wireshark-the-easy-way/
- 125. Others • h2c (and wiretapping): - https://github.com/fstab/h2c • h2a: reverse proxy - https://github.com/summerwind/h2a • Conformance: - https://github.com/summerwind/h2spec • Serves and proxies: - Charles proxy: https://www.charlesproxy.com - MITM proxy: https://mitmproxy.org/ - h2o: https://h2o.examp1e.net/ - Envoy: https://www.envoyproxy.io/ • http-wg - https://github.com/http2/http2-spec/wiki/Tools
- 126. Is this EVER going to end??!!
- 127. What’s next?
- 128. 0.9 1.0 1.1 2.0 HTTP complexity HTTP version
- 129. 0.9 1.0 1.1 2.0 HTTP complexity My age HTTP version
- 131. QUIC
- 132. QUIC
- 133. gQUIC vs iQUIC
- 134. gQUIC vs iQUIC • Monolithic • Google proprietary • Modularized • IETF standard
- 135. IP TCP UDP TLS HTTP/2 QUIC TCP-like congestion avoidance, recovery HTTP/2 shim UDP QUIC TCP-like congestion avoidance, recovery Application (HTTP/2) QUIC crypto TLS 1.3 gQUIC iQUIChttp/2 https://datatracker.ietf.org/meeting/98/materials/slides-98-edu-sessf-quic-tutorial/
- 137. The promise of QUIC • Low latency connection setup - 0RTT • UDP - Addresses TCP’s head of line blocking in h2 - More flexible congestion avoidance algorithms - “rich signaling for congestion control and loss recovery” • Everything authenticated and encrypted • Mitigating middle box tomfoolery • Connection migration and NAT rebinding (via connection IDs)
- 138. Some QUIC reading • https://dl.acm.org/citation.cfm?id=3098842 • https://quicwg.github.io/ • https://github.com/quicwg • And a video: https://vimeo.com/227461189
- 139. So… • Has much changed? • Do we still have a lot to learn? • Do we still have a lot to do? • QUIC will fix everything, right?
- 140. Thank you