2017-09-09

Stocator: A High Performance Object Store Connector for Spark


Behind Picton Street

IBM have published a lovely paper on their Stocator 0-rename committer for Spark

Stocator is:
  1. An extended Swift client
  2. magic in their FS to redirect mkdir and file PUT/HEAD/GET calls under the normal MRv1 __temporary paths to new paths in the dest dir
  3. generating dest/part-0000 filenames using the attempt & task attempt ID to guarantee uniqueness and to ease cleanup: restarted jobs can delete the old attempts
  4. Commit performance comes from eliminating the COPY, which is O(data),
  5. And from tuning back the number of HTTP requests (probes for directories, mkdir 0 byte entries, deleting them)
  6. Failure recovery comes from explicit names of output files. (note, avoiding any saving of shuffle files, which this wouldn't work with...spark can do that in memory)
  7. They add summary data in the _SUCCESS file to list the files written & so work out what happened (though they don't actually use this data, instead relying on their swift service offering list consistency). (I've been doing something similar, primarily for testing & collection of statistics).

Page 10 has their benchmarks, all; of which are against an IBM storage system, not real amazon S3 with its different latencies and performance.

Table 5: Average run time


Read-Only 50GB
Read-Only 500GB
Teragen
Copy
Wordcount
Terasort
TPC-DS
Hadoop-Swift Base
37.80±0.48
393.10±0.92
624.60±4.00
622.10±13.52
244.10±17.72
681.90±6.10
101.50±1.50
S3a Base
33.30±0.42
254.80±4.00
699.50±8.40
705.10±8.50
193.50±1.80
746.00±7.20
104.50±2.20
Stocator
34.60±0.56
254.10±5.12
38.80±1.40
68.20±0.80
106.60±1.40
84.20±2.04
111.40±1.68
Hadoop-Swift Cv2
37.10±0.54
395.00±0.80
171.30±6.36
175.20±6.40
166.90±2.06
222.70±7.30
102.30±1.16
S3a Cv2
35.30±0.70
255.10±5.52
169.70±4.64
185.40±7.00
111.90±2.08
221.90±6.66
104.00±2.20
S3a Cv2 + FU
35.20±0.48
254.20±5.04
56.80±1.04
86.50±1.00
112.00±2.40
105.20±3.28
103.10±2.14

The S3a is the 2.7.x version, which has the stabilisation enough to be usable with Thomas Demoor's fast output stream (HADOOP-11183). That stream buffers in RAM & initiates the multipart upload once the block size threshold is reached. Provided you can upload data faster than you run out of RAM, it avoids the log waits at the end of close() calls, so has significant speedup. (The fast output stream has evolved into the S3ABlockOutput Stream (HADOOP-13560) which can buffer off heap and to HDD, and which will become the sole output stream once the great cruft cull of HADOOP-14738 goes in)

That means in the doc, "FU" == fast upload, == incremental upload & RAM storage. The default for S3A will become HDD storage, as unless you have a very fast pipe to a compatible S3 store, it's easy to overload the memory

Cv2 means MRv2 committer, the one which does  single rename operation on task commit (here the COPY), rather than one in task commit to promote that attempt, and then another in job commit to finalise the entire job. So only: one copy of every byte PUT, rather than 2, and the COPY calls can run in parallel, often off the critical path

 Table 6: Workload speedups when using Stocator



Read-Only 50GB
Read-Only 500GB
Teragen
Copy
Wordcount
Terasort
TPC-DS
Hadoop-Swift Base
x1.09
x1.55
x16.09
x9.12
x2.29
x8.10
x0.91
S3a Base
x0.96
x1.00
x18.03
x10.33
x1.82
x8.86
x0.94
Stocator
x1
x1
x1
x1
x1
x1
x1
Hadoop-Swift Cv2
x1.07
x1.55
x4.41
x2.57
x1.57
x2.64
x0.92
S3a Cv2
x1.02
x1.00
x4.37
x2.72
x1.05
x2.64
x0.93
S3a Cv2 + FU
x1.02
x1.00
x1.46
x1.27
x1.05
x1.25
x0.93


Their TCP-DS benchmarks show that stocator & swift is slower than TCP-DS Hadoop 2.7 S3a + Fast upload & MRv2 commit. Which means that (a) the Hadoop swift connector is pretty underperforming and (b) with fadvise=random and columnar data (ORC, Parquet) that speedup alone will give better numbers than swift & stocator. (Also shows how much the TCP-DS Benchmarks are IO heavy rather than output heavy the way the tera-x benchmarks are).

As the co-author of that original swift connector then, what the IBM paper is saying is "our zero rename commit just about compensates for the functional but utterly underperformant code Steve wrote in 2013 and gives us equivalent numbers to 2016 FS connectors by Steve and others, before they started the serious work on S3A speedup". Oh, and we used some of Steve's code to test it, removing the ASF headers.

Note that as the IBM endpoint is neither the classic python Openstack swift or Amazon's real S3, it won't exhibit the real issues those two have. Swift has the worst update inconsistency I've ever seen (i.e repeatable whenever I overwrote a large file with a smaller one), and aggressive throttling even of the DELETE calls in test teardown. AWS S3 has its own issues, not just in list inconsistency, but serious latency of HEAD/GET requests, as they always go through the S3 load balancers. That is, I would hope that IBM's storage offers significantly better numbers than you get over long-haul S3 connections. Although it'd be hard (impossible) to do a consistent test there, I 'd fear in-EC2 performance numbers to be actually worse than that measures.

I might post something faulting the paper, but maybe I'll should to do a benchmark of my new committer first. For now though, my critique of both the swift:// and s3a:// clients is as follows

Unless the storage services guarantees consistency of listing along with other operations, you can't use any of the MR commit algorithms to reliably commit work. So performance is moot. Here IBM do have a consistent store, so you can start to look at performance rather than just functionality. And as they note, committers which work with object store semantics are the way to do this: for operations like this you need the atomic operations of the store, not mocked operations in the client.

People who complain about the performance of using swift or s3a as a destination are blisfully unaware of the key issue: the risk of data loss due inconsistencies. Stocator solves both issues at once.

Anyway, means we should be planning a paper or two on our work too, maybe even start by doing something about random IO and object storage, as in "what can you do for and in columnar storage formats to make them work better in a world where a seek()+ read is potentially a new HTTP request."

(picture: parakeet behind Picton Street)






2017-05-22

Dissent is a right: Dissent is a duty. @Dissidentbot

It looks like the Russians interfered with the US elections, not just from the alleged publishing of the stolen emails, or through the alleged close links with the Trump campaign, but in the social networks, creating astroturfed campaigns and repeating the messages the country deemed important.

Now the UK is having an election. And no doubt the bots will be out. But if the Russians can do bots: so can I.

This then, is @dissidentbot.
Dissidentbot

Dissident bot is a Raspbery Pi running a 350 line ruby script tasked with heckling politicans
unrelated comments seem to work, if timely
It offers:
  • The ability to listen to tweets from a number of sources: currently a few UK politicians
  • To respond pick a random responses from a set of replies written explicitly for each one
  • To tweet the reply after a 20-60s sleep.
  • Admin CLI over Twitter Direct Messaging
  • Live update of response sets via github.
  • Live add/remove of new targets (just follow/unfollow from the twitter UI)
  • Ability to assign a probability of replying, 0-100
  • Random response to anyone tweeting about it when that is not a reply (disabled due to issues)
  • Good PUE numbers, being powered off the USB port of the wifi base station, SSD storage and fanless naturally cooled DC. Oh, and we're generating a lot of solar right now, so zero-CO2 for half the day.
It's the first Ruby script of more than ten lines I've ever written; interesting experience, and I've now got three chapters into a copy of the Pickaxe Book I've had sitting unloved alongside "ML for the working programmer".  It's nice to be able to develop just by saving the file & reloading it in the interpreter...not done that since I was Prolog programming. Refreshing.
Strong and Stable my arse
Without type checking its easy to ship code that's broken. I know, that's what tests are meant to find, but as this all depends on the live twitter APIs, it'd take effort, including maybe some split between Model and Control. Instead: broken the code into little methods I can run in the CLI.

As usual, the real problems surface once you go live:
  1. The bot kept failing overnight; nothing in the logs. Cause: its powered by the router and DD-WRT was set to reboot every night. Fix: disable.
  2. It's "reply to any reference which isn't a reply itself" doesn't work right. I think it's partly RT related, but not fully tracked it down.
  3. Although it can do a live update of the dissident.rb script, it's not yet restarting: I need to ssh in for that.
  4. I've been testing it by tweeting things myself, so I've been having to tweet random things during testing.
  5. Had to add handling of twitter blocking from too many API calls. Again: sleep a bit before retries.
  6. It's been blocked by the conservative party. That was because they've been tweeting 2-4 times/hour, and dissidentbot originally didn't have any jitter/sleep. After 24h of replying with 5s of their tweets, it's blocked.
The loopback code is the most annoying bug; nothing too serious though.

The DM CLI is nice, the fact that I haven't got live restart something which interferes with the workflow.
  Dissidentbot CLI via Twitter DM
Because the Pi is behind the firewall, I've no off-prem SSH access.

The fact the conservatives have blocked me, that's just amusing. I'll need another account.

One of the most amusing things is people argue with the bot. Even with "bot" in the name, a profile saying "a raspberry pi", people argue.
Arguing with Bots and losing

Overall the big barrier is content.  It turns out that you don't need to do anything clever about string matching to select the right tweet: random heckles seems to blend in. That's probably a metric of political debate in social media: a 350 line ruby script tweeting random phrases from a limited set is indistinguishable from humans.

I will accept Pull Requests of new content. Also: people are free to deploy their own copies. without the self.txt file it won't reply to any random mentions, just listen to its followed accounts and reply to those with a matching file in the data dir.

If the Russians can do it, so can we.

2017-05-15

The NHS gets 0wned

Friday's news was full of breaking panic about an "attack" on the NHS, making it sound like someone had deliberately made an attempt to get in there and cause damage.

It turns out that it wasn't an attack against the NHS itself, just a wide scale ransomware attack which combined click-through installation and intranet propagation by way of a vulnerability which the NSA had kept for internal use for some time.

Laptops, Lan ports and SICP

The NHS got decimated for a combination of issues:
  1. A massive intranet for SMB worms to run free.
  2. Clearly, lots of servers/desktops running the SMB protocol.
  3. One or more people reading an email with the original attack, bootstrapping the payload into the network.
  4. A tangible portion of the machines within some parts of the network running unpatched versions of Windows, clearly caused in part by the failure of successive governments to fund a replacement program while not paying MSFT for long-term support.
  5. Some of these systems within part of medical machines: MRI scanners, VO2 test systems, CAT scanners, whatever they use in the radiology dept —to name but some of the NHS machines I've been through in the past five years.
The overall combination then is: a large network/set of networks with unsecured, unpatched targets were vulnerable to a drive-by attack, the kind of attack, which, unlike a nation state itself, you may stand a chance of actually defending against.

What went wrong?

Issue 1: The intranet. Topic for another post.

Issue 2: SMB.

In servers this can be justified, though it's a shame that SMB sucks as a protocol. Desktops? It's that eternal problem: these things get stuck in as "features", but which sometimes come to burn you. Every process listening on a TCP or UDP port is a potential attack point. A 'netstat -a" will list running vulnerabilities on your system; enumerating running services "COM+, Sane.d? mDNS, ..." which you should review and decide whether they could be halted. Not that you can turn mDNS off on a macbook...

Issue 3: Email

With many staff, email clickthrough is a function of scale and probability: someone will, eventually. Probability always wins.

Issue 4: The unpatched XP boxes.

This is why Jeremy Hunt is in hiding, but it's also why our last Home Secretary, tasked with defending the nation's critical infrastructure, might want to avoid answering questions. Not that she is answering questions right now.

Finally, 5: The medical systems.

This is a complication on the "patch everything" story because every update to a server needs to be requalified. Why? Therac-25.

What's critical here is that the NHS was 0wned, not by some malicious nation state or dedicated hacker group: it fell victim to drive-by ransomware targeted at home users, small businesses, and anyone else with a weak INFOSEC policy This is the kind of thing that you do actually stand a chance of defending against, at least in the laptop, desktop and server.

Untitled

Defending against malicious nation state is probably near-impossible given physical access to the NHS network is trivial: phone up at 4am complaining of chest pains and you get a bed with a LAN port alongside it and told to stay there until there's a free slot in the radiology clinic.

What about the fact that the NSA had an exploit for the SMB vulnerability and were keeping quiet on it until the Shadow Brokers stuck up online? This is a complex issue & I don't know what the right answer is.

Whenever critical security patches go out, people try and reverse engineer them to get an attack which will work against unpatched versions of: IE, Flash, Java, etc. The problems here were:
  • the Shadow Broker upload included a functional exploit, 
  • it was over the network to enable worms, 
  • and it worked against widely deployed yet unsupported windows versions.
The cost of developing the exploit was reduced, and the target space vast, especially in a large organisation. Which, for a worm scanning and attacking vulnerable hosts, is a perfect breeding ground.

If someone else had found and fixed the patch, there'd still have been exploits out against it -the published code just made it easier and reduced the interval between patch and live exploit

The fact that it ran against an old windows version is also something which would have existed -unless MSFT were notified of the issue while they were still supporting WinXP. The disincentive for the NSA to disclose that is that a widely exploitable network attack is probably the equivalent of a strategic armament, one step below anything that can cut through a VPN and the routers, so getting you inside a network in the first place.

The issues we need to look at are
  1. How long is it defensible to hold on to an exploit like this?
  2. How to keep the exploit code secure during that period, while still using it when considered appropriate?
Here the MSFT "tomahawk" metaphor could be pushed a bit further. The US govt may have tomahawk missiles with nuclear payloads, but the ones they use are the low-damage conventional ones. That's what got out this time.

WMD in the Smithsonia

One thing that MSFT have to consider is: can they really continue with the "No more WinXP support" policy? I know they don't want to do it, the policy of making customers who care paying for the ongoing support is a fine way to do it, it's just it leaves multiple vulnerabilites. People at home, organisations without the money and who think "they won't be a target", and embedded systems everywhere -like a pub I visited last year whose cash registers were running Windows XP embedded; all those ATMs out there, etc, etc.

Windows XP systems are a de-facto part of the nation's critical infrastructure.

Having the UK and US governments pay for patches for the NHS and everyone else could be a cost effective way of securing a portion of the national infrastructure, for the NHS and beyond.

(Photos: me working on SICP during an unplanned five day stay and the Bristol Royal Infirmary. There's a LAN port above the bed I kept staring at; Windows XP Retail packaging, Smithsonian aerospace museum, the Mall, Washington DC)

2017-05-05

Is it time to fork Guava? Or rush towards Java 9?

Lost Crew WiP

Guava problems have surfaced again.

Hadoop 2.x has long-shipped Guava 14, though we have worked to ensure it runs against later versions, primarily by re-implementing our own classes of things pulled/moved across versions.


Hadoop trunk has moved up to Guava 21.0, HADOOP-10101.This has gone and overloaded the Preconditions.checkState() method, such that: if you compile against Guava 21, your code doesn't link against older versions of Guava. I am so happy about this I could drink some more coffee.

Classpaths are the gift that keeps on giving, and any bug report with the word "Guava" in it is inevitably going to be a mess. In contrast, Jackson is far more backwards compatible; the main problem there is getting every JAR in sync.

What to do?

Shade Guava Everywhere
This is going too be tricky to pull off. Andrew Wang has taken on this task. this is one of those low level engineering projects which doesn't have press-release benefits but which has the long-term potential to reduce pain. I'm glad someone else is doing it & will keep an eye on it.

Rush to use Java 9
I am so looking forward to this from an engineering perspective:

Pull Guava out
We could do our own Preconditions, our own VisibleForTesting attribute. More troublesome are the various cache classes, which do some nice things...hence they get used. That's a lot of engineering.

Fork Guava
We'd have to keep up to date with all new Guava features, while reinstating the bits they took away. The goal: stuff build with old Guava versions still works.

I'm starting to look at option four. Biggest issue: cost of maintenance.

There's also the fact that once we use our own naming "org.apache.hadoop/hadoop-guava-fork" then maven and ivy won't detect conflicting versions, and we end up with > 1 version of the guava JARs on the CP, and we've just introduced a new failure mode.

Java 9 is the one that has the best long-term potential, but at the same time, the time it's taken to move production clusters onto Java 8 makes it 18-24 months out at a minimum. Is that so bad though?

I actually created the "Move to Java 9": JIRA in 2014. It's been lurking there, Akira Ajisaka doing the equally unappreciated step-by-step movement towards it.

Maybe I should just focus some spare-review-time onto Java 9; see what's going on, review those patches and get them in. That would set things up for early adopters to move to Java 9, which, for in-cloud deployments, is something where people can be more agile and experimental.

(photo: someone painting down in Stokes Croft. Lost Crew tag)

2017-04-12

Mocking: an enemy of maintenance

Bristol spring

I'm keeping myself busy right now with HADOOP-13786, an O(1) committer for job output into S3 buckets. The classic filesystem relies on rename() for that, but against S3 rename is a file-by-file copy whose time is O(data) and whose failure mode is "a mess", amplified by the fact that an inconsistent FS can create the illusion that destination data hasn't yet been deleted: false conflict.
. This creates failures like SPARK-18512., FileNotFoundException on _temporary directory with Spark Streaming 2.0.1 and S3A, as well as long commit delays.

I started this work a while back, making changes into the S3A Filesystem to support it. I've stopped focusing on that committer, and instead pulled in the version which Netflix have been using, which has the advantages of a thought out failure policy, and production testing. I've been busy merging that with the rest of the S3A work, and am now at the stage where I'm switching it over to the operations I've written for the first attempt, the "magic committer". These are in S3A, where they integrate with S3Guard state updates, instrumentation and metrics, retry logic, etc etc. All good.

The actual code to do the switchover is straightforward. What is taking up all my time is fixing the mock tests. These are failing with false positives "I've broken the code", when really the cause is "these mock tests are too brittle". In particular, I've had to rework how the tracking of operations goes, as a Mock Amazon S3Ciient is no longer used by the committer, instead its associated with the FS instance, which then is shared by all operations in a single test method. And the use of S3AFS methods shows up where its failing due to the mock instance not initing properly. I ended up spending most of Tuesday simply implementing the abort() call, now I'm doing the same on commit(). The production code switches fine, it's just the mock stuff.

This has really put me off mocking. I have used it sporadically in the past, and I've occasionally had to work other people's. Mocking has some nice features
  • Can run in unit tests which don't need AWS credentials, so Yetus/Jenkins can run them on patches.
  • Can be used to simulate failures and validate outcomes.
But the disadvantage is I just think they are too high maintenance. One test I've already migrated to being an integration test against an object store; I retained the original mock one, but just deleted that yesterday as it was going to be too expensive to migrate, and, with
that IT test, obsolete.

The others, well: the changes for abort() should help, but every new S3A method that gets called triggers new problems which I need to address. This is, well, "frustrating".

It's really putting me off mocking. Ignoring the Jenkins aspect, the key benefit is structure fault injection. I believe I could implement that in the IT tests too, at least in those tests which run in the same JVM. If I wanted to, I could probably even do it in the forked VMs by f propagating details on the desired failures to the processes. Or, if I really wanted to be devious, by running an HTTP proxy in the test VM and simulating network failures for the AWS client code itself to hit. That wouldn't catch all real-world problems (DNS, routing), but I could raise authentication, transient HTTP failures, and of course, force in listing inconsistencies. This is tempting, because it will help me qualify the AWS SDK we depend on, and could be re-used for testing the Azure storage too. Yes, it would take effort —but given the cost of maintaining those Mock tests after some minor refactoring of the production code, it's starting to look appealing.

(photo: Garage door, Greenbank, Bristol)

2017-04-11

The interruption economy

With the untimely death of a laptop in Boston in February, I've rebuilt two laptops recently.

The first: a replacement for the dead one: a development macbook pro wired up to the various bits of work infra: MS office, VPN,  even hipchat. The second, a formerly dead 2009 macbook brought back to life with a 256GB SSD and a boost of its RAM to 8GB (!).

Doing this has brought home to be a harsh truth

The majority of applications you install on an OSX laptop consider it not just a right, but a duty, to interrupt you while you are trying to work.

It's not just the things where someone actually want's to talk  to (e.g. skype), it's pretty much everything you can install

For example, iTunes wants to be able to interrupt me, including playing sounds. It's a music player application, and it also wants to make beeping noises? Same for spotify. Why should background music apps or foreground media playback apps think they need to be able to interrupt you when they are running in the background?

iTunes wants to interrupt me

Dropbox. I didn't realise this was doing notifications until it suddenly popped up to tell me the good news that it was keeping itself up to date automatically.

Dropbox interrupting me with a random fact

Keeping your installation up to date is something we should expect all applications to do. It should not be so important that you should pop up a dialog box "good news, you are only at risk from 0-day exploits we haven't found or patched yet!". Once I was aware that dropbox was happy to interrupt me, I went to its settings, only to discover that it also wants to interrupt me on "comments, share's and @mentions", and on synced files.
Dropbox wants to harass me

I hadn't noticed that a tool I used to sync files across machines had evolved into a groupware app where people could @mention me, but clearly it has, and in teams, interruptions whenever someone comments on things is clearly considered good. It also wants to interrupt me on files syncing. Think about that. We have an application whose primary purpose is "synchronising files across machines", and suddenly it wants to start popping up notifications when it is doing its job? What else should we have? Note taking applications sharing the good news that they haven't crashed yet?
Apple Notes wants to interrupt me

Maybe, because amongst the apps which also consider interruption and inalienable right are: OneNote and macOS notes app. I have no idea what they want to interrupt me about: Notes doesn't specify what it wants to alert me about, only that it wants to notify me on locked screens and make a noise. OneNote? Lets you spec which notebooks can trigger interrupts, but again, the why is missing.

The list goes on. My password manager, text editor, IDE. Everything I install defaults to interrupting me.

Yes, you can turn the features off, but on a newly installed machine, that means that you have to go through every single app and disable every single interruption point. Miss out some small detail and while you are trying to get some work done, something pops up to say "lucky you! Something has happened which Photos thinks it is so important you should stop what you are doing and use it instead!". when you are building up two laptops, it means there's about 20+ times I've had to bring up the notifications preference pane, scroll down to whichever app last interrupted me, turn off all its notifications, then continue until something else chooses to break my concentration.

The web browsers want to let web pages interrupt you too.

Firefox you can't disable it, at least not without delving into about:config.

Firefox doesn't seem to let me utterly disable interrupts

You can block it in the OS notifications settings, which implies it is at least integrated with the OS and the system-wide do-not-disturb feature.


Chrome: you can manage it in the browser —even though google don't want you to stop it, but it doesn't appear to  integrated with the OS;

Google chrome recommends interruptiblity

With the OS integration, OSX's do-not-disturb feature won't work. will work here, so if you do let Chrome notify you, webapps gain the right to interrupt you during presentations, watching media content, etc.
Safari lets you disable web site notifications, you just have to clear the check box
Safari? Permitted, but OS controlled, completely blockable. This doesn't mean that webapps shouldn't be able to interrupt you: google calendar is a good example, it's just the easier we make it to do this, the more sites will want to.


The OS isn't even consistent itself. There is no way to tell time machine to not annoy you with the fact that it hasn't updated for 11 days. It's not part of the notification system, even though it came from the same building. What kind of example is that to set for others?


Because the default behaviour of every application is to interrupt, I have to go through every single installed app to disable it else my life is a constant noise of popups stating irrelevant facts. You may not notice that as you install one application at a time, turning off the settings individually, but when you build up a new box, the arrogance of all these applications becomes obvious, as it takes some time to actually stop your attention being attacked by the software you install.

Getting users to look at your app, your web site, is roped in as "The attention economy". That certainly applies to things like twitter, facebook, snapchat, etc. But how does translate into dropbox trying to get my attention to tell me that it's keeping itself up to date? Or whatever itunes or photos wants to interrupt me on? Why does OneNote need to tell me something about a saved workbook? This isn't "the attention economy". This is "interruption economy": people terrified that users may not be making full use of their features, so trying to keep popping up to encourage you to use the app or whatever new feature they've just installed

Interrupting people while they are trying to work is not a good use of the life of people whose work depends on "getting things done without interruptions". As my colleagues should know, though some of them forget, I don't run with hipchat on precisely because I hate getting popups "hey Steve, can i just ask..." , where the ask is something that I'd google for the answer myself, so why somebody asks me to google for them, I don't know. But even with the workflow interrupts off, things keep trying to stop me getting anything done

Then there's the apps which interrupt without any warning at all. I got caught out at this at Dataworks summit, where halfway through a presentation GPGMail popped up telling me there was a new version. This was a presentation where I'd explicitly set "do not disturb" on and war running full screen, but GPG mail checks weren't using it. Lesson: turn off the wifi as well as setting everything to do-not-disturb/offline.

Those update prompts, they are important. But everything keeps going "update me! now!" they end up being an irritant to ignore, just like the way the "service now!" alert pops up our car when we use it. It's just another low-level hint, not something which matters like "low pressure in tyres".

What it does really highlight is that having an applications keep itself up to date with security patches is still considered, on OSX, to be something worth interrupting the user to let them know about. All I can say it's a good thing that Linux apps don't feel the same way, or apt-get upgrade would be unbearable.

 
Finally, there's the OS
  • It'd be good if the OS recognised when a full screen media/presentation app was underway and automatically went into silent mode at that point.
  • All the OS's own notifications "upgrade available", "no time machine backups" should be integrated with the same notification mechanisms for app viewers. That's to help the users, but also set an example for all others.

What to to really do about it?

I'd really like to be able to tell the OS that the default settings for any newly installed app is "no notifications". Maybe now I've built up the laptops I won't have to go through the torment of disabling it across many apps, so it'll just be that case by case irritant. Even so, there's still the pain of being reminded of update options even

What I can do though, is promise not to personally write applications which interrupt people by default.

Here then, is my pledge:
  1. I pledge to give my users the opportunity to live a life free of interruptions, at least from my own code.
  2. I pledge not to write applications which bring up notification boxes to tell you that they have kept themselves up to date automatically, that someone has logged in to another machine, or that someone else is viewing a document a user has co-authored.
  3. Ideally, the update mech should integrate that from the OS, and so it can handle the notifications (or not).
  4. If I then add a notifications in an application for what I consider to be relevant information, I pledge for the default state to be "don't".
  5. They will all go away when left alone.
  6. Furthermore, I pledge to use the OS supplied mechanism and integrate with any do- not-disturb mechanism the OS implements.
I know, I haven't done do client side code for a long time, but I can assure people, if I did: I'd try to be much less annoying than what we have today. Because I recognise how much pain this causes.

    2017-03-02

    The Great S3 Outage of February 2017

    On tuesday the world split into different groups
    1. Those who knew that S3 was down, and the internet itself was in crisis.
    2. Those who knew that some of the web sites and phone apps they used weren't working right, but didn't know why.
    3. Those who didn't notice and wouldn't have cared.

    I was obviously in group 1, the engineers, who whisper to each other, "where were you when S3 went down".
    S3 Outage: Increased Error Rate


    I was running the latest hadoop--aws s3a tests, and noticed as some of my tests were failing. Not the ones to s3 Ireland, but those against the landsat bucket we use in lots of our hadoop test as it is a source of a 20 MB CSV file where nobody has to pay download fees, or spend time creating a 20 MB CSV file. Apparently there are lots of landsat images too, but our hadoop tests stop at: seeking in the file. I've a spark test which does the whole CSV parse thing., as well as one I use in demos as an example not just of dataframes against cloud data, but of how data can be dirty, such as with a cloud cover of less than 0%.

    Partial test failures: never good.

    It was only when I noticed that other things were offline that I cheered up: unless somehow my delayed-commit multipart put requests had killed S3: I wasn't to blame. And with everything offline I could finish work at 18:30 and stick some lasagne in the oven. (I'm fending for myself & keeping a teenager fed this week).

    What was impressive was seeing how deep it went into things. Strava app? toast. Various build tools and things? Offline.

    Which means that S3 wasn't just a SPOF for my own code, but a lot of transitive dependencies, meaning that things just weren't working -all the way up the chain.

    S3 Outage: We can update our status page

    S3 is clearly so ubiquitous a store that the failure of US-East enough to have major failures, everywhere.

    Which makes designing to be resilient to an S3 outage so hard: you not only have to make your own system somehow resilient to failure, you have to know how your dependencies cope with such problems. For which step one is: identify those dependencies.

    Fortunately, we all got to find out on Tuesday.

    Trying to mitigate against a full S3A outage is probably pretty hard. At the very least,
    1. replicated front end content across different S3 installations would allow you to present some kind of UI.
    2. if you are collecting data for processing, then a contingency plan for the sink being offline: alternate destinations, local buffering, discarding (nifi can be given rules here).
    3. We need our own status pages which can be updated even if the entire infra we depend on is missing. That is: host somewhere else, have multiple people with login rights, so an individual isn't the SPOF. Maybe even a facebook page too, as a final backup
    4. We can't trust the AWS status page no more.
    Is it worth putting in lots of effort to eliminating an S3 outage as a SPOF? Well, the failure rate is such that it's a lot of effort for a very rare occurence. If you are user facing, some app like strava, maybe it's easiest to say "no". If you are providing a service for others though, availability, or at least the ability to degrade QoS is something to look at.

    Anyway, we can now celebrate the fact that the entire internet now runs in four places: AWS, Google, Facebook and Azure. And we know what happens when one of them goes offline.