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colmmacc's profile
Colm MacCárthaigh
Colm MacCárthaigh
Colm MacCárthaigh
@colmmacc

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Colm MacCárthaigh

@colmmacc

AWS, Apache, Crypto, Irish Music, Haiku, Photography

Seattle
notesfromthesound.com
Joined April 2008

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    1. Colm MacCárthaigh‏ @colmmacc 7 Dec 2018
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      Before building great systems, you need to build a great team. Strive for fearlessness, That means a no blame, no shame, awesome positive atmosphere ... and then translate that into action and calculated risk taking ... the safety to try new things and new ideas.pic.twitter.com/dgA6g6tXfy

      2 replies 15 retweets 50 likes
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    2. Colm MacCárthaigh‏ @colmmacc 7 Dec 2018
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      But DON'T risk taking with security, durability, or availability. Those are core values, and top priorities that need to be inviolable. Take risks with business ideas and features, and product names, and have some fun!pic.twitter.com/yWfZSaMyh0

      1 reply 7 retweets 39 likes
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    3. Colm MacCárthaigh‏ @colmmacc 7 Dec 2018
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      With that context, let's build some stable and reliable control systems! What do we use them for? 4 common reasons: 1/ lifecycling resources (launching, scaling, etc) 2/ deploying system config 3/ deploying software 4/ deploying user settings.pic.twitter.com/00uaBoD3mr

      1 reply 2 retweets 11 likes
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    4. Colm MacCárthaigh‏ @colmmacc 7 Dec 2018
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      At Amazon, we encourage merging 2 and 3. Deploying systems config, like global feature flags, *IS* deploying software. So where possible, we use the same system for both. We have awesome awesome deployment safety systems. One-boxing, staggering, rollback, etc. So use it for both!pic.twitter.com/kyv7AmwPUP

      2 replies 2 retweets 17 likes
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    5. Colm MacCárthaigh‏ @colmmacc 7 Dec 2018
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      For building control systems, it turns out there's a whole branch of rigorous engineering called control theory. There's a lot of math, and it is awesome, well worth knowing, but also you don't need all of that to get most of the benefit. Here is what is worth knowing ...pic.twitter.com/LtjZtIMs1J

      1 reply 1 retweet 11 likes
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    6. Colm MacCárthaigh‏ @colmmacc 7 Dec 2018
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      Every stable control system needs 3 things: a measurement process, a controller, and an actuator. Basically something to see how the world is, something to figure out how the world needs to change, and something that makes that change happen.pic.twitter.com/cuZP7dJLdr

      1 reply 3 retweets 28 likes
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    7. Colm MacCárthaigh‏ @colmmacc 7 Dec 2018
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      That simple mental model is very very important. Most control systems built by CS people *don't* have a measurement element. Like the remote control we've already seen! These systems propagate errors they can't correct. BAD BAD.

      1 reply 1 retweet 13 likes
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    8. Colm MacCárthaigh‏ @colmmacc 7 Dec 2018
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      So always start with the idea of a measurer; poll every server to know what state it is in, check if the user settings get there, etc ... and build the system as something that corrects any errors it sees, not just a system that just blindly shouts instructions.

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    9. Colm MacCárthaigh‏ @colmmacc 7 Dec 2018
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      O.k. that's 80% of control theory right there for you. The next 10% is that controllers are very sensitive to lag. Imagine a furnace that heated your boiler based on the temperature it was an hour ago? It'd be very unstable!pic.twitter.com/4GJ21YM7uu

      2 replies 1 retweet 11 likes
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    10. Mairi of the Gorgonites‏ @Sailor_Mairi 7 Dec 2018
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      Replying to @colmmacc

      So, random aside: It is possible to actually have control systems that are too responsive. If you'd like, I can go into why that is a thing with boilers, even!

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      Colm MacCárthaigh‏ @colmmacc 7 Dec 2018
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      Replying to @Sailor_Mairi

      Yes please! Especially if you're going to get into hysteresis!

      10:22 AM - 7 Dec 2018
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        2. Mairi of the Gorgonites‏ @Sailor_Mairi 7 Dec 2018
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          Replying to @colmmacc

          Well, in a marine boiler, reacting to changes too quickly can mean that if you are doing maneuvers, and thus many quick changes in the throttle, a computer controlled boiler might wind up producing too much or not enough steam.

          1 reply 0 retweets 0 likes
        3. Mairi of the Gorgonites‏ @Sailor_Mairi 7 Dec 2018
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          Replying to @Sailor_Mairi @colmmacc

          Generally, you go for long periods of time (hours, days) without changing throttle setting at all. You're either going at cruising speed or sitting still at the dock. But, there are periods where you do have quite a lot of changes in the throttle.

          1 reply 0 retweets 0 likes
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