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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 10 Sep 2018
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      Well, no, sometimes servers are down and errors happen, so you need a workflow engine to drive retries. Oh and that implies you have some way to tell if the change even made it there, so you need a poller or a pusher or something to monitor config propagation status. YOU GET ME.

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    2. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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      But then we build all that, and it works, and changes get integrated and customer configs change in seconds, and WE'RE GOOD, RIGHT?

      1 reply 0 retweets 5 likes
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    3. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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      We're good until one day we're not. Imagine a big event happens, maybe a power outage, or a spike on the internet due to the Super Bowl or something, and for whatever reason a bunch of customers all try to make changes at the same time?

      1 reply 0 retweets 7 likes
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    4. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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      The API gets choked, the workflow gets backed up, the status monitors start to lag. OUCH. Even worse, some customers start undoing their changes because they don't see them happening quickly. Now we have pointless changes stuck in the system that no-one even wants!! OUCH OUCH.

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    5. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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      Now, let's try a much better, O(1) control plane. DUMB AS ROCKS. Imagine if instead that the customer API pretty much edits a document directly, like a file on S3 or whatever. And imagine the servers just pull that file every few seconds, WHETHER IT CHANGED OR NOT.

      2 replies 1 retweet 14 likes
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    6. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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      This system is O(1). The whole config can change, or none of it, and the servers don't even care. They are dumb. They just carry on. This is MUCH MUCH more robust.

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    7. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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      It never lags, it self-heals very quickly, and it's always ready for a set of events like everyone changing everything at once. The SYSTEM DOES NOT CARE.

      1 reply 1 retweet 20 likes
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    8. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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      This is how we build the most critical control planes at AWS. For example if you use Route 53 health checks, or rely on NLB, or NAT GW, the underlying health statuses are *ALWAYS* being pushed around as a bitset. ALWAYS ALWAYS.

      3 replies 6 retweets 32 likes
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    9. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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      A few statuses can change (which is normal), and the system reacts, or they can ALL change, and it will react just the same (which is abnormal). We could have lots of targets suddenly disappear .... break ...

      2 replies 0 retweets 6 likes
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    10. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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      "I felt a great disturbance in the Force, as if millions of voices suddenly cried out in terror and were suddenly silenced. I fear something terrible has happened."

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      Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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      ... end break ... and the system does not care or even know how many changed! It just works. Very very reliable, and unde-rapreciated.

      12:23 PM - 10 Sep 2018
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      • Roberto Iturralde Chase Hughes Garrett Wilkin Andre Caron Amaury Ortega Alex Max DeLiso Deirdre Connolly¹ Calum Leslie
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        1. New conversation
        2. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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          BONUS CONTENT: O.k., what does this have to do with Maxwell's Daemon? WHAT EVEN IS THAT? Well the first kind of constant time problem, for crypto, is an example of minimizing information theoretical entropy. It's about minimizing perceptible disorder and what is computable.

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        3. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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          The second is more like traditional thermodynamic entropy. With a constant-time control plane, we're trying to build a system that has a constant temperature, because it's always doing the same amount of work.

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        4. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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          Ok now if I lost you with that, here's the simple version: when systems change a lot, they undergo stress, and getting stressed at the worst times, like under attacks or in the middle of outages, is really bad. At a high level these problems are the same.

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        5. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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          And it turns out at a low level they are the same too! Information theoretical entropy, which is all about computability and bits, can be related to thermodynamic entropy, which is all about energy and work!

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        6. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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          How? Well Maxwell proposed a thought experiment that showed a problem with thermodynamics. He imagined two rooms side by side, at even temperatures. He posited that a daemon, a ghost, could open a door between the two rooms and let faster moving molecules over to one side.

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        7. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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          This sort of disproved existing thermodynamics, because the work it takes to open a door like that is less than the energy transferred due to the faster molecules changing sides. This was unresolved for a long time ... UNTIL ...

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        8. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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          A bunch of folks showed that you don't just open the door, you have to observe and predict, and therefore COMPUTE, the position of the molecule. THIS TAKES ENERGY ... and they showed that the energy it takes is at least equivalent to the difference.

          2 replies 1 retweet 7 likes
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        9. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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          So in a big old nuts, strange-loop sort of way, these completely unrelated things are totally the same at both a MACRO and MICRO level. This blows my mind .... but may also make no sense ;-)

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        10. Colm MacCárthaigh‏ @colmmacc 10 Sep 2018
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          O.k. that's it, and AMA if you want! Oh and @threadreaderapp please unroll this mess I made.

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        11. End of conversation

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