How Slack Works

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Keith Adams takes a tour of Slack's infrastructure, from native and web clients, through the edge, into the Slack datacenter, and around the various services that provide real-time messaging, search, voice calls, and custom emoji.

This presentation was recorded at QCon San Francisco 2016.

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*Timestamps*



0:00 Intro (Keith Adams)

1:26 Agenda
2:37 Scale and Style


6:18 Architecture Overview

8:19 Logging in

14:11 MySQL Shards
18:18 RTM.start payload

19:51 Message server
24:32 Deferring Work
27:39 Putting it all together


31:41 Challenges

32:59 Challenge 1: Mains Failure

34:14 Challenge 2: Rtm.start for large teams

35:02 Challenge 3: Mass reconnects



Plan of attacks
35:50 Scale-out mains
37:04 Rtm.start for large teams
38:33 Mass reconnects

41:45 Stuff left out
43:19 Wrapping up

44:20 Questions

[wonderstruck.]

Very interesting talk. Usually you hear people from huge established companies discussing massive arch migrations, or brand new startups showing off their flashy new stack.

This was a very humble, grounded talk on what it’s like to work in a real system architecture—what works for them, and what could be improved as they scale.

[tommyls]

I love how articulate he is. He comes across as a smart guy. I'd like to work with him.

[SuperNash]

Slack in 2016 was a pretty new app, and I completely respect the devs decisions to favor faster deployment. I have experience with a product which is almost 10 yr+ old and - we are still scrambling for DB alerts.

[BillaCode]

I realised after 4 years of experience working in software field, I still don't have basic knowledge of making a high scalable app. Great video, thanks for sharing this great knowledge

[sanjay_nk]

Handling great scale with simplicity in design. Excellent !!

[janvikalra_]

SUPER insightful and detailed deep dive. thanks for sharing!

[simonc]

At 18:00, can someone help me understand what he means by the left and right heads, writing left and writing right?

[augusto]

I just wish the "Microsoft Teams" would watch this and learn to not suck

[shimaozheng]

@12:19 what does it mean when he mentioned the time to the shard is arbitrary? It means it just randomly picks up a shard and record it? What's the benefit of doing in this way vs. consistent hashing?

[pengdu]

this may be a dumb question but why is there a message server in the first place? why a separate service?

[lokthar]

a PHP Monolith?

Slack is a really great piece of Software but those design decisions though..

[tenshiangel]

Would prefer to use Discord, but beggars can't always be choosers. Oh well.

[Dstonephoto]

Sweet lord, this is the most SV-esque mumble job ever.

[VahidOnTheMove]

Poor presentation. He shows a slide and talks about something else.

[phenomenal]

Lol is slack still even a thing or in business? Pretty sure the markets owned by Microsoft teams now.

[jvm-tv]

It works for them and obviously a successful product but God! what a boring architecture! I wouldn't want to work there.

[SreeAn]

too boring, nothing much to learn for people preparing for system design interviews. I wasted 20 minutes, don't do that mistake.