Wednesday, September 16, 2020

The missing OS


When I joined Google in 2011, I quoted a quip of a friend of mine:
"There are roughly one and a half computers in the world, and Google has one of them."
The world has changed quite a bit since 2011, and there may possibly be half a dozen computers in the world now. That said, for the following text to make sense, when I say "the computer", I mean a very large assembly of individual machines that have been connected to make them act like one computer.

Actual blog post:

The tech landscape of modern microservice deployments can be confusing - it is fast-changing, with a proliferation of superficially similar projects claiming to do similar things. Even to me as someone fairly deeply into technology, it isn't always clear what precise purpose the different projects serve.

I've quipped repeatedly about "Datacenter OS" (at least here and here), and mused about it since I first left Google for my sabbatical in 2015. I recently had the chance to chat with a bunch of performance engineers (who sit very much at the crossing between Dev and Ops), and they reminded me to write up my thoughts. This is a first post, but there may be more coming (particularly on the security models for it).

Warning: This post is pure, unadulterated opinion. It is full of unsubstantiated unscientific claims. I am often wrong.

I claim the following:
When we first built computers, it took a few decades until we had the first real "operating systems". Before a 'real' OS emerged, there were a number of proto-OS -- collections of tools that had to be managed separately and cobbled together. There were few computers overall in the world, and if you wanted to work on one, you had to work at a large research institution or organization. These machines ran cobbled-together OSs that were unique to that computer.

Since approximately 2007, we're living through a second such period: The "single computer" model is replaced with "warehouse-sized computers". Initially, few organizations had the financial heft to have one of them, but cloud computing is making "lots of individual small computers" accessible to many companies that don't have a billion of cash for a full datacenter.

The hyperscalers (GOOG, FB, but also Tencent etc.) are building approximations to a "proto-datacenter-OS" internally; Amazon is externalizing some of theirs, and a large zoo of individual components for a Datacenter-OS exist as open-source projects.

What does not exist yet is an actual complete DatacenterOS that "regular" companies can just install.

There is a "missing OS" - a piece of software that you install on a large assembly of computers, and that transform this assembly of computers into "one computer".

What would a "Datacenter OS" consist of? If you look at modern tech stacks, you find that there is a surprising convergence - not in the actual software people are running, but in the "roles" that need to be filled. For each role, there are often many different available implementations.

The things you see in every large-scale distributed infrastructure are:

  1. Some form of cluster-wide file system. Think GFS/Colossus if you are inside Google, GlusterFS or something like it if you are outside. Many companies end up using S3 because the available offerings aren't great.
  2. A horizontally scalable key-value store. Think BigTable if you are inside Google, or Cassandra, or Scylla, or (if you squint enough) even ElasticSearch.
  3. A distributed consistent key-value store. Think Chubby if you are inside Google, or etcd if you are outside. This is not directly used by most applications and mostly exists to manage the cluster.
  4. Some sort of pub/sub message queuing system. Think PubSub, or in some sense Kafka, or SQS on AWS, or perhaps RabbitMQ.
  5. A job scheduler / container orchestrator. A system that takes the available resources, and all the jobs that ought to be running, and a bunch of constraints, and then solves a constrained bin-packing optimization problem to make sure resources are used properly. Think Borg, or to some extent Kubernetes. This may or may not be integrated with some sort of MapReduce-style batch workload infrastructure to make use of off-peak CPU cycles.

I find it very worthwhile to think about "what other pieces do I have on a single-laptop-OS that I really ought to have on the DatacenterOS?".

People are building approximations of a process explorer via Prometheus and a variety of other data collection agents.

One can argue that distributed tracing (which everybody realizes they need) is really the Datacenter-OS-strace (and yes, it is crucially important). The question "what is my Datacenter-OS-syslog" is similarly interesting. 

A lot of the engineering that goes into observability is porting the sort of introspection capabilities we are used to having on a single machine to "the computer".

Is this "service mesh" that people are talking about just the DatacenterOS version of the portmapper?

There are other things for which we really have no idea how to build the equivalent. What does a "debugger" for "the computer" look like? Clearly, single-stepping on a single host isn't the right way to fix problems in modern distributed systems - your service may be interacting with dozens of other hosts that may be crashing at the same time (or grinding to a halt or whatever), and re-starting and single-stepping is extremely difficult.

Aside from the many monitoring, development, and debugging tools that need to be rebuilt for "the computer", there are many other - even more fundamental - questions that really have no satisfactory answer. Security is a particularly uncharted territory:

What is a "privileged process" for this computer? What are the privilege and trust boundaries? How does user management work? How does cross-service authentication and credential delegation work? How do we avoid re-introducing literally every logical single-machine privilege escalation that James Forshaw describes in his slides into our new OS and the various services running there? Is there any way that a single Linux Kernel bug in /mm does not spell doom for our entire security model?

To keep the post short:

In my opinion, the emerging DatacenterOS is the most exciting thing that has happened in computer science in decades. I sometimes wish I was better at convincing billionaires to give me a few hundred million dollars to invest in interesting problems -- because if there is a problem that I think I'd love to work on, it'd be a FOSS DatacenterOS - "install this on N machines, and you have 'a computer'".

A lot of the technological landscape is easier to understand if one asks the question: What function in "the computer" does this particular piece of the puzzle solve? What is the single-machine equivalent of this project?

This post will likely have follow-up posts, because there are many more ill-thought-out ideas I have on the topic:

  • Security models for a DatacenterOS
  • Kubernetes: Do you want to be the scheduler, or do you want to be the OS? Pick one.
  • How do we get the power of bash scripting, but for a cluster of 20k machines?




Friday, August 14, 2020

My Twitter-Discussion-Deescalation Policy

Twitter is great, and Twitter is terrible. While it enables getting in contact and starting loose discussions with a great number of people, and while it has certainly helped me broaden my perspectives and understanding of many topics, it also has a lot of downsides.

Most importantly, Twitter discussions, due to their immediacy of feedback and the fact that everybody is busy, often end up in shouting matches where "learning from each other while discussing a topic" (the actual purpose of a discussion) is forgotten.

Most importantly: Twitter can be very repetitive, and it can be very difficult to convey the context for complex topics - and nobody has time to repeat all the context in each Twitter discussion.

Today, I am recovering from a migraine attack that coincided with my kid having a cranky night, and as a result, I cut a few Twitter discussions short. The people on the receiving end of this "short-cutting" may rightly feel slighted, so I am writing this blog post in preparation for future similar situations.

There are some topics (often related to security or economics) about which I have thought for a reasonably long time. Particularly for security, we're talking about a few decades of hands-on experience with a fairly obsessive work on the topic, both on the theoretical and on the practical side. Rooted in this experience, I sometimes make statements on Twitter. These statements may be in conflict with what other people (you?) may think, and we may engage in a discussion. It is possible, though, that we will reach a point in the discussion where my feeling is "oh, in order to convey my point, I'd now need to spend 25 minutes conveying the context necessary for my point, and I only have a few hours in my day after I deduct sleep and other obligations".

At this point, I need to make a judgement call: Do I invest that time? I also need to make the call without having the most important context: Does the other side care about understanding me at all?

So if we end up in a Twitter discussion, and I reply to you with a link to this blog post at some point, please understand: I have run out of time to spend on this Twitter thread, and I need to cut the discussion short because conveying the necessary context is too time consuming without knowing that this is actually desired, and that our discussion is a mutual learning exercise.

If you very much care about the topic, and about understanding the perspective I have, I will happily schedule a 25-minute video call to discuss in person, and will obviously make an effort to understand your perspective, too. My DM's are open, ping me and I will send you a calendly link.

Monday, May 18, 2020

My self-help guide to making sense of a confusing world

It has become painfully evident over the last decade or so that social media has a somewhat corrosive effect on "truth" and "discussion". There are a variety of reasons for this - many unidentified - but a few factors are:
  1. For every opinion, no matter how bizarre, it has become easy to find a community with similar beliefs.
  2. The discoverability of almost all information coupled with the shortening of attention spans allows people with strange beliefs to search for information at - at least if only glanced at for 15 seconds - may be interpreted to confirm their strange belief.
  3. Algorithms that maximize engagement also maximize enragement -- if the algorithms show me content that draws me into a time-sink discussions with no benefit, they are "winning" (in terms of the metrics against which they are evaluated).
  4. The social media platforms favor "immediacy of feedback" vs. taking time to think things through. Social media discussions often devolve into name-calling or rapid-fire quoting of dubious studies without any qualitative understanding - people quote papers and sources they never critically evaluated.
Aside from that, creating false but engagement-producing content has become a veritable industry. Attention can be monetized, so one can earn good money by making up lies that appear credible to some subset of the population. The quality of mainstream reporting has been caught up in this downward spiral.

The result of this is "fake news" and the "death of a consensus on reality"; strange conspiracy theories; and generally many many hours wasted. The problem cuts across class and educational layers; it is simply not true that "only the uneducated" fall prey to internet falsehoods.

Personally, I am terrified of believing things that are not true. I am not quite sure why; but to assuage my fears of misleading myself, I have adapted a number of habits to function as checks on my own beliefs.

By and large, I have found them very useful.

In this blog post, I intend to share my thoughts on how people mislead themselves, and the checks I have decided to apply to my own beliefs. I am not always successful, but this is the bar I try to measure myself against. My hope is that this is helpful for others; perhaps it can help reject false beliefs somewhere.

So let's begin with an underlying assumption I make:

People tend to believe in things that help them.

As a young man I believed that people try to understand a situation, and then form a belief based on that. This is not what I observed in my life. My observation is that people choose beliefs and systems of belief to fulfill a function for them.

My father is born in the 30s in Germany, and as a pre-teen and early teen, he got a front-row seat to watch all adults perform an ideological 180-degree turn in front of him. The question of "how do people adjust their beliefs" has always been important in my discussions with him.

My conclusion is that people are very good at identifying what they want, and what is beneficial to them. They also like to feel good about themselves, and about what they do. Given these constraints, people tend to pick beliefs and systems of belief that ...
  • ... allow them to do what they want to do.
  • ... allow them to reap benefits.
  • ... allow them to feel good about themselves at the same time.
I alluded to this with the sentence "Everybody wants to be the hero of their own story" in my disclosure Rashomon post.

It is crucially important to be aware that belief systems have a functional role for those that believe them. This is why it can be so hard to "convince" anyone of the incorrectness of their belief system: You are asking the person to give up more than a false belief - often, you are asking the person to adjust their view of themselves as being less benign than they like to believe, or you are asking the person to adjust their view in a manner that would cast doubt on their ability to obtain some other benefit.

When I write "people" above, this includes you and me.

Being aware of the functional role of beliefs is hence important when you investigate your own beliefs (more on that later). Trying to believe what makes us feel good is the most fundamental cognitive bias.

So what am I trying to do to counter that bias? Here's my list of 7 habits:
  1. Clarify your beliefs
  2. Ask about the benefits of your beliefs
  3. Seek out original sources
  4. Examine evidence for your beliefs and competing hypotheses
  5. What new information would change your beliefs?
  6. Provide betting odds
  7. Discuss for enlightenment, not "winning"

Habit 1: Clarify beliefs

It may sound odd, but it takes conscious effort to turn everyday diffuse "belief" into an actual clearly articulated statement. For me, nothing quite clarifies thoughts like writing them down - often things that appear clear and convincing in my head turn out to be quite muddled and unstructured when I try to put them to paper.

Asking oneself the question "what are my beliefs on a given topic", and trying to write them down coherently, is surprisingly powerful. It forces a deliberate effort to determine what one actually believes, and committing to that belief in writing (at least to oneself).

Habit 2: Ask about the benefits of your beliefs - "am I the baddie?"

Awareness of the functional role of beliefs is important when examining one's own beliefs. Feynman famously said about science that "the first principle is that you must not fool yourself and you are the easiest person to fool".

When examining my own beliefs, it try to ask myself: What benefits does this belief bestow on me? What does this belief permit me to do? How does this belief make me feel good about myself?

It is quite often helpful to actively try to examine alternative narratives in which one casts oneself in a bad light. Trying to maintain our positive image of ourselves is a strong bias; making a conscious effort at examining alternate, unflattering narratives can be helpful.

My wife and me sometimes jokingly play "mock custody battle" - a game where we jokingly try to portray each other as some sort of terrible person and reinterpret each others entire biography as that of a villain - and it is quite enlightening.

Habit 3: Seek out original sources, distrust secondary reporting

Both for things like presidential debates and for scientific papers, the secondary reporting is often quite incorrect. In political debates, it is often much less relevant how the debate went and what happened -- only a small fraction of the population will have witnessed the event. What really counts is the narrative that gets spun around what happened.

You can observe this during election season in the US, where as soon as the debate is over, all sides will try to flood all the talkshows and newscasts with their "narrative" (which has often been pre-determined prior to the debate happening - "He is a flip-flopper. He flipflops." or something along those lines).

Likewise, scientific papers often get grossly misrepresented in popular reporting, but also by people that only superficially read the paper. Reporting is often grossly inaccurate, and if you are an expert on a topic, you will notice that on your topic of expertise, reporting is often wrong; at the same time, we somehow forget about this and assume that it is more accurate on topics where we are not experts (the famous "Gell-Mann amnesia").

A friend of mine (scientist himself) recently forwarded me a list of papers that estimated COVID-19 IFR; one of them reported an IFR of 0%. Closer examination of the contents of the paper revealed that they examined blood from blood donors for antibodies; nobody that died of COVID-19 went to donate blood 2 weeks later, so clearly there were no fatalities in their cohort.

Nonetheless, the paper was cited as "evidence that the IFR is lower than people think".

A different friend sent me a "scientific paper" that purported to show evidence that tetanus vaccines had been laced with a medication to cause infertility. Examining the paper, it was little than assembling a bunch of hearsay; no experimental setup, no controlling, no alternative hypothesis etc. Examining the homepages of the authors revealed they were all strange cranks, peddling various strange beliefs. It was "published" in a "we accept everything" journal.

Acquiring the habit to read original sources is fascinating - there are bookshelves full of books that are quoted widely, mostly by people who have never read them (Sun Tzu, Clausewitz, and the Bible are probably the most common). It is also useful: Getting into the habit of reading original papers helps cut out the middle-man and start judging the results directly; it is also a good motivator to learn a good bit of statistics.


Habit 4: Examine evidence for your beliefs, analyze competing hypotheses

Once one's own beliefs are clarified in writing, and one has looked at the primary sources, one can gather evidence for one's belief.

While one does so, one should also make a deliberate effort to gather and entertain competing hypotheses: What other explanations for the phenomenon under discussion exist? What are hypotheses advanced by others?

Given one's own beliefs, and alternate hypotheses, one can look at the evidence supporting each of them carefully.

Two principles help me at this stage to discount less-credible hypotheses (including my own):
  • Occam's Razor: Often, the simpler explanation is the more likely explanation
  • Structural malice: Malicious individuals are pretty rare, but if an incentive structure exists where an individual can benefit from malice while explaining it away, the tendency is for that to happen.
  • Incompetence is much more common than competent malice. The Peter principle and Parkinsons law apply to human organisations.
After this step, I end up forming an opinion - looking at the various competing hypotheses, I re-examine which I find most credible. Often, but not always, it is the beliefs that I declared initially, but with reasonable frequency I have to adjust my beliefs after this step.

Habit 5: What new information would change my opinion?

John Maynard Keynes is often quoted with "When the facts change, I change my mind; what do you do, Sir?". It is worth examining what would be necessary to change one's beliefs ahead of time.

Given my belief on a subject right now, what new information would need to be disclosed to me for me to change my mind?

This is very helpful to separate "quasi-religious" beliefs from changeable beliefs.

Habit 6: Provide betting odds

This is perhaps the strangest, but ultimately one of my more useful points. Over the last years, I have read a bit about the philosophy of probability; particularly De Finetti's "Philosophical Lectures on Probability".

When we speak about "probability", we actually mean two different things: The fraction for a given outcome if we can repeat an experiment many times (coin-flip etc.), and the strength of belief that a given thing is true or will happen in situations where the experiment cannot be repeated.

These are very different things - the former has an objective truth, the second one is fundamentally subjective.

At the same time, if my subjective view of reality is accurate, I will assign good probability values (in the 2nd sense) to different events. ("Good" here means that if a proper scoring rule was applied, I would do well).

Beliefs carry little cost, and little accountability. Betting provides cost for being wrong, and accountability about being wrong.

This means that if I truly believe that my beliefs are correct, I should be willing to bet on them; and through the betting odds I provide, I can quantify the strength of my belief.

For me, going through the exercise of forcing myself to provide betting odds has been extremely enlightening: It forced me to answer the question "how strongly do I actually believe this?".

In a concrete example: Most currently available data about COVID-19 hints at an IFR of between 0.49% and 1% (source) with a p-value of < 0.001. My personal belief is that the IFR is almost certainly >= 0.5%. I am willing to provide betting odds of 3:1 (meaning of you bet against me, you get 3x the payout) for the statement "By the end of 2022, when the dust around COVID-19 has settled, the empirical IFR for COVID-19 will have been greater than 0.5%".

This expresses strong belief in the statement (much better than even odds), but some uncertainty around the estimate in the paper (the p-value would justify much more aggressive betting odds).

(Be aware that these betting odds are only valid for the next 4 days, as my opinion may change).

To sum up: Providing betting odds is a great way of forcing oneself to confront one's own strength of belief. If I believe something, but am unwilling to bet on it, why would that be the case? If I believe something, and am unwilling to provide strong odds in favor of that belief, why is that the case? Do I really believe these things if I am unwilling to bet?

Habit 7: Discuss for enlightenment, not "winning"

When I was young, my father taught me that the purpose of a discussion is never to win, or even to convince. The purpose of a discussion is to understand - the topic under discussion, or the position of the other side, or a combination thereof. This gets lost a lot in modern social media "debates".
Social media encourages participating in discussions and arguing a side without ever carefully thinking about one's view on a topic. The memoryless and repetitive nature of the medium allows one to spend countless hours re-hashing the same arguments over and over, without making any advance, and ignoring any thought-out arguments that may have been put in writing.

After few weeks after the "Rashomon of Disclosure"-post, a Twitter discussion about disclosure erupted; and I upset a few participants by more or less saying: "Y'know, I spent the time writing down my thoughts and arguments around the topic, and I am very willing to engage with anybody that is willing to spend the time writing down their thoughts and arguments, but I am not willing to engage in Twitter yelling matches where we ignore all the nuance and just whip up tribal sentiment."

This was not universally well-received, but refusal to engage in social media yelling matches and the dopamine kick that arises from the immediacy of the experience is an important step if we want to understand either the topic or the other participants in the debate.


This was a very long-winded post. Thank you for having read this far. I hope this post will be helpful - perhaps some of the habits can be useful to others. If not, this blog post can at least explain why I will sometimes withdraw from social media discussions, and insist on long-form write ups as a means of communication. It should also be helpful to reduce bewilderment if I offer betting odds in surprising situations.

Friday, March 20, 2020

Before you ship a "security mitigation" ...

Hey everybody,

During my years doing vulnerability research and my time in Project Zero, I frequently encountered proposals for new security mitigations. Some of these were great, some of these - were not so great.

The reality is that most mitigations or "hardening" features will impose a tax on someone, somewhere, and quite possibly a heavy one. Many security folks do not have a lot of experience running reliable infrastructure, and some of their solutions can break things in production in rather cumbersome ways.

To make things worse, many mitigations are proposed and implemented with very handwavy and non-scientific justifications - "it makes attacks harder", it "raises the bar", etc., making it difficult or impossible for third parties to understand the design and trade-offs considered during the design.

Over the years, I have complained about this repeatedly, not least in this Twitter thread:

This blog post is really just a recapitulation of the Twitter thread:

Below are rules I wrote for a good mitigation a while ago: “Before you ship a mitigation...

  1. Have a design doc for a mitigation with clear claims of what it intends to achieve. This should ideally be something like "make it impossible to achieve reliable exploitation of bugs like CVE1, CVE2, CVE3", or similar; claims like "make it harder" are difficult to quantify. If you can't avoid such statements, quantify them: "Make sure that development of an exploit for bugs like CVE4, CVE5 takes more than N months".
  2. Pick a few historical bugs (ideally from the design doc) and involve someone with solid vuln-dev experience; give him a 4-8 full engineering weeks to try to bypass the mitigation when exploiting historical bugs. See if the mitigation holds, and to what extent. Most of the time, the result will be that the mitigation did not live up to the promise. This is good news: You have avoided imposing a tax on everybody (in complexity, usability, performance) that provides no or insufficient benefit.
  3. When writing the code for the mitigation, *especially* when it touches kernel components, have a very stringent code review with review history. The reviewer should question any unwarranted complexity and ask for clarification.
    Follow good coding principles - avoid functions with hidden side effects that are not visible from the name etc. - the stringency of the code review should at least match the stringency of a picky C++ readability reviewer, if not exceed it.”

There are also these three slides to remember:
In short: Make it easy for people to understand the design rationale behind the mitigation. Make sure this design rationale is both accessible, and easily debated / discussed. Be precise and quantifiable in your claims so that people can challenge the mitigation on it's professed merits.