docker run glyph/rproxy

Want to TLS-protect your co-located stack of vanity websites with Twisted and Let's Encrypt using HawkOwl's rproxy, but can't tolerate the bone-grinding tedium of a pip install? I built a docker image for you now, so it's now as simple as:

$ mkdir -p conf/certificates;
$ cat > conf/rproxy.ini << EOF;
> [rproxy]
> certs=certificates
> http_ports=80
> https_ports=443
> [hosts]
> mysite.com_host=<other container host>
> mysite.com_port=8080
$ docker run --restart=always -v "$(pwd)"/conf:/conf \
    -p 80:80 -p 443:443 \

There are no docs to speak of, so if you're interested in the details, see the tree on github I built it from.

Modulo some handwaving about docker networking to get that <other container host> IP, that's pretty much it. Go forth and do likewise!

As some of you may have guessed from the unintentional recent flurry of activity on my Twitter account, twitter feed, the service I used to use to post blog links automatically, is getting end-of-lifed. I've switched to for the time being, unless they send another unsolicited tweetstorm out on my behalf...

Sorry about the noise! In the interests of putting some actual content here, maybe you would be interested to know that I was recently interviewed for PyDev of the Week?

Hitting The Wall

Dinner with friends is an endurance sport.

I’m an introvert.

I say that with a full-on appreciation of just how awful thinkpieces on “introverts” are.

However, I feel compelled to write about this today because of a certain type of social pressure that a certain type of introvert faces. Specifically, I am a high-energy introvert.

Cementing this piece’s place in the hallowed halls of just awful thinkpieces, allow me to compare my mild cognitive fatigue with the plight of those suffering from chronic illness and disability1. There’s a social phenomenon associated with many chronic illnesses, “but you don’t LOOK sick”, where well-meaning people will look at someone who is suffering, with no obvious symptoms, and imply that they really ought to be able to “be normal”.

As a high-energy introvert, I frequently participate in social events. I go to meet-ups and conferences and I engage in plenty of public speaking. I am, in a sense, comfortable extemporizing in front of large groups of strangers.

This all sounds like extroverted behavior, I know. But there’s a key difference.

Let me posit two axes for personality type: on the X axis, “introvert” to “extrovert”, and on the Y, “low energy” up to “high energy”.

The X axis describes what kinds of activities give you energy, and the Y axis describes how large your energy reserves are for the other type.

Notice that I didn’t say which type of activity you enjoy.

Most people who would self-describe as “introverts” are in the low-energy/introvert quadrant. They have a small amount of energy available for social activities, which they need to frequently re-charge by doing solitary activities. As a result of frequently running out of energy for social activities, they don’t enjoy social activities.

Most people who would self-describe as “extroverts” are also on the “low-energy” end of the spectrum. They have low levels of patience for solitary activity, and need to re-charge by spending time with friends, going to parties, etc, in order to have the mental fortitude to sit still for a while and focus. Since they can endlessly get more energy from the company of others, they tend to enjoy social activities quite a bit.

Therefore we have certain behaviors we expect to see from “introverts”. We expect them to be shy, and quiet, and withdrawn. When someone who behaves this way has to bail on a social engagement, this is expected. There’s a certain affordance for it. If you spend a few hours with them, they may be initially friendly but will visibly become uncomfortable and withdrawn.

This “energy” model of personality is of course an oversimplification - it’s my personal belief that everyone needs some balance of privacy and socialization and solitude and eventually overdoing one or the other will be bad for anyone - but it’s a useful one.

As a high-energy introvert, my behavior often confuses people. I’ll show up at a week’s worth of professional events, be the life of the party, go out to dinner at all of them, and then disappear for a month. I’m not visibily shy - quite the opposite, I’m a gregarious raconteur. In fact, I quite visibly enjoy the company of friends. So, usually, when I try to explain that I am quite introverted, this claim is met with (quite understandable) skepticism.

In fact, I am quite functionally what society expects of an “extrovert” - until I hit the wall.

In endurance sports, one is said to “hit the wall” at the point where all the short-term energy reserves in one’s muscles are exhausted, and there is a sudden, dramatic loss of energy. Regardless, many people enjoy endurance sports; part of the challenge of them is properly managing your energy.

This is true for me and social situations. I do enjoy social situations quite a bit! But they are nevertheless quite taxing for me, and without prolonged intermissions of solitude, eventually I get to the point where I can no longer behave as a normal social creature without an excruciating level of effort and anxiety.

Several years ago, I attended a prolonged social event2 where I hit the wall, hard. The event itself was several hours too long for me, involved meeting lots of strangers, and in the lead-up to it I hadn’t had a weekend to myself for a few weeks due to work commitments and family stuff. Towards the end I noticed I was developing a completely flat affect, and had to start very consciously performing even basic body language, like looking at someone while they were talking or smiling. I’d never been so exhausted and numb in my life; at the time I thought I was just stressed from work.

Afterwards though, I started having a lot of weird nightmares, even during the daytime. This concerned me, since I’d never had such a severe reaction to a social situation, and I didn’t have good language to describe it. It was also a little perplexing that what was effectively a nice party, the first half of which had even been fun for me, would cause such a persistent negative reaction after the fact. After some research, I eventually discovered that such involuntary thoughts are a hallmark of PTSD.

While I’ve managed to avoid this level of exhaustion before or since, this was a real learning experience for me that the consequences of incorrectly managing my level of social interaction can be quite severe.

I’d rather not do that again.

The reason I’m writing this, though3, is not to avoid future anxiety. My social energy reserves are quite large enough, and I now have enough self-knowledge, that it is extremely unlikely I’d ever find myself in that situation again.

The reason I’m writing is to help people understand that I’m not blowing them off because I don’t like them. Many times now, I’ve declined or bailed an invitation from someone, and later heard that they felt hurt that I was passive-aggressively refusing to be friendly.

I certainly understand this reaction. After all, if you see someone at a party and they’re clearly having a great time and chatting with everyone, but then when you invite them to do something, they say “sorry, too much social stuff”, that seems like a pretty passive-aggressive way to respond.

You might even still be skeptical after reading this. “Glyph, if you were really an introvert, surely, I would have seen you looking a little shy and withdrawn. Surely I’d see some evidence of stage fright before your talks.”

But that’s exactly the problem here: no, you wouldn’t.

At a social event, since I have lots of energy to begin with, I’ll build up a head of steam on burning said energy that no low-energy introvert would ever risk. If I were to run out of social-interaction-juice, I’d be in the middle of a big crowd telling a long and elaborate story when I find myself exhausted. If I hit the wall in that situation, I can’t feel a little awkward and make excuses and leave; I’ll be stuck creepily faking a smile like a sociopath and frantically looking for a way out of the converstaion for an hour, as the pressure from a large crowd of people rapidly builds up months worth of nightmare fuel from my spiraling energy deficit.

Given that I know that’s what’s going to happen, you won’t see me when I’m close to that line. You won’t be in at my desk when I silently sit and type for a whole day, or on my couch when I quietly read a book for ten hours at a time. My solitary side is, by definition, hidden.

But, if I don’t show up to your party, I promise: it’s not you, it’s me.

  1. In all seriousness: this is a comparison of kind and not of degree. I absolutely do not have any illusions that my minor mental issues are a serious disability. They are - by definition, since I do not have a diagnosis - subclinical. I am describing a minor annoyance and frequent miscommunication in this post, not a personal tragedy. 

  2. I’ll try to keep this anonymous, so hopefully you can’t guess - I don’t want to make anyone feel bad about this, since it was my poor time-management and not their (lovely!) event which caused the problem. 

  3. ... aside from the hope that maybe someone else has had trouble explaining the same thing, and this will be a useful resource for them ... 

Probably best to get this out of the way before this weekend:

If I meet you at a technical conference, you’ll probably see me extend my elbow in your direction, rather than my hand. This is because I won’t shake your hand at a conference.

People sometimes joke about “con crud”, but the amount of lost productivity and human misery generated by conference-transmitted sickness is not funny. Personally, by the time the year is out, I will most likely have attended 5 conferences. This means that if I get sick at each one, I will spend more than a month out of the year out of commission being sick.

When I tell people this, they think I’m a germophobe. But, in all likelihood, I won’t be the one getting sick. I already have 10 years of building up herd immunity to the set of minor ailments that afflict the international Python-conference-attending community. It’s true that I don’t particularly want to get sick myself, but I happily shake people’s hands in more moderately-sized social gatherings. I’ve had a cold before and I’ve had one again; I have no illusion that ritually dousing myself in Purell every day will make me immune to all disease.

I’m not shaking your hand because I don’t want you to get sick. Please don’t be weird about it!

A Container Is A Function Call

There’s something missing from the Docker ecosystem: a type-checker.

It seems to me that the prevailing mental model among users of container technology1 right now is that a container is a tiny little virtual machine. It’s like a machine in the sense that it is provisioned and deprovisioned by explicit decisions, and we talk about “booting” containers. We configure it sort of like we configure a machine; dropping a bunch of files into a volume, setting some environment variables.

In my mind though, a container is something fundamentally different than a VM. Rather than coming from the perspective of “let’s take a VM and make it smaller so we can do cool stuff” - get rid of the kernel, get rid of fixed memory allocations, get rid of emulated memory access and instructions, so we can provision more of them at higher density... I’m coming at it from the opposite direction.

For me, containers are “let’s take a program and made it bigger so we can do cool stuff”. Let’s add in the whole user-space filesystem so it’s got all the same bits every time, so we don’t need to worry about library management, so we can ship it around from computer to computer as a self-contained unit. Awesome!

Of course, there are other ecosystems that figured this out a really long time ago, but having it as a commodity within the most popular server deployment environment has changed things.

Of course, an individual container isn’t a whole program. That’s why we need tools like compose to put containers together into a functioning whole. This makes a container not just a program, but rather, a part of a program. And of course, we all know what the smaller parts of a program are called:


A container of course is not the function itself; the image is the function. A container itself is a function call.

Perceived through this lens, it becomes apparent that Docker is missing some pretty important information. As a tiny VM, it has all the parts you need: it has an operating system (in the docker build) the ability to boot and reboot (docker run), instrumentation (docker inspect) debugging (docker exec) etc. As a really big function, it’s strangely anemic.

Specifically: in every programming language worth its salt, we have a type system; some mechanism to identify what parameters a function will take, and what return value it will have.

You might find this weird coming from a Python person, a language where

def foo(a, b, c):
    return a.x(c.d(b))

is considered an acceptable level of type documentation by some3; there’s no requirement to say what a, b, and c are. However, just because the type system is implicit, that doesn’t mean it’s not there, even in the text of the program. Let’s consider, from reading this tiny example, what we can discover:

  • foo takes 3 arguments, their names are “a”, “b”, and “c”, and it returns a value.
  • Somewhere else in the codebase there’s an object with an x method, which takes a single argument and also returns a value.
  • The type of <unknown>.x’s argument is the same as the return type of another method somewhere in the codebase, <unknown-2>.d

And so on, and so on. At runtime each of these types takes on a specific, concrete value, with a type, and if you set a breakpoint and single-step into it with a debugger, you can see each of those types very easily. Also at runtime you will get TypeError exceptions telling you exactly what was wrong with what you tried to do at a number of points, if you make a mistake.

The analogy to containers isn’t exact; inputs and outputs aren’t obviously in the shape of “arguments” and “return values”, especially since containers tend to be long-running; but nevertheless, a container does have inputs and outputs in the form of env vars, network services, and volumes.

Let’s consider the “foo” of docker, which would be the middle tier of a 3-tier web application (cribbed from a real live example):

FROM pypy:2
RUN apt-get update -ym
RUN apt-get upgrade -ym
RUN apt-get install -ym libssl-dev libffi-dev
RUN pip install virtualenv
RUN mkdir -p /code/env
RUN virtualenv /code/env
RUN pwd

COPY requirements.txt /code/requirements.txt
RUN /code/env/bin/pip install -r /code/requirements.txt
COPY main /code/main
RUN chmod a+x /code/main

VOLUME /site
VOLUME /etc/ssl/private

ENTRYPOINT ["/code/main"]

In this file, we can only see three inputs, which are filesystem locations: /clf, /site, and /etc/ssl/private. How is this different than our Python example, a language with supposedly “no type information”?

  • The image has no metadata explaining what might go in those locations, or what roles they serve. We have no way to annotate them within the Dockerfile.
  • What services does this container need to connect to in order to get its job done? What hostnames will it connect to, what ports, and what will it expect to find there? We have no way of knowing. It doesn’t say. Any errors about the failed connections will come in a custom format, possibly in logs, from the application itself, and not from docker.
  • What services does this container export? It could have used an EXPOSE line to give us a hint, but it doesn’t need to; and even if it did, all we’d have is a port number.
  • What environment variables does its code require? What format do they need to be in?
  • We do know that we could look in requirements.txt to figure out what libraries are going to be used, but in order to figure out what the service dependencies are, we’re going to need to read all of the code to all of them.

Of course, the one way that this example is unrealistic is that I deleted all the comments explaining all of those things. Indeed, best practice these days would be to include comments in your Dockerfiles, and include example compose files in your repository, to give users some hint as to how these things all wire together.

This sort of state isn’t entirely uncommon in programming languages. In fact, in this popular GitHub project you can see that large programs written in assembler in the 1960s included exactly this sort of documentation convention: huge front-matter comments in English prose.

That is the current state of the container ecosystem. We are at the “late ’60s assembly language” stage of orchestration development. It would be a huge technological leap forward to be able to communicate our intent structurally.

When you’re building an image, you’re building it for a particular purpose. You already pretty much know what you’re trying to do and what you’re going to need to do it.

  1. When instantiated, the image is going to consume network services. This is not just a matter of hostnames and TCP ports; those services need to be providing a specific service, over a specific protocol. A generic reverse proxy might be able to handle an arbitrary HTTP endpoint, but an API client needs that specific API. A database admin tool might be OK with just “it’s a database” but an application needs a particular schema.
  2. It’s going to consume environment variables. But not just any variables; the variables have to be in a particular format.
  3. It’s going to consume volumes. The volumes need to contain data in a particular format, readable and writable by a particular UID.
  4. It’s also going to produce all of these things; it may listen on a network service port, provision a database schema, or emit some text that needs to be fed back into an environment variable elsewhere.

Here’s a brief sketch of what I want to see in a Dockerfile to allow me to express this sort of thing:

FROM ...
RUN ...

LISTENS ON: TCP:80 FOR: org.ietf.http/
CONNECTS TO: pgwritemaster.internal ON: TCP:5432 FOR: org.postgresql.db/
CONNECTS TO: {{ETCD_HOST}} ON: TCP:{{ETCD_PORT}} FOR: com.coreos.etcd/client-communication
ENVIRONMENT NEEDS: ETCD_HOST FORMAT: HOST(com.coreos.etcd/client-communication)
ENVIRONMENT NEEDS: ETCD_PORT FORMAT: PORT(com.coreos.etcd/client-communication)
VOLUME AT: /logs FORMAT: org.w3.clf REQUIRES: WRITE UID: 4321

An image thusly built would refuse to run unless:

  • Somewhere else on its network, there was an etcd host/port known to it, its host and port supplied via environment variables.
  • Somewhere else on its network, there was a postgres host, listening on port 5432, with a name-resolution entry of “pgwritemaster.internal”.
  • An environment variable for the etcd configuration was supplied
  • A writable volume for /logs was supplied, owned by user-ID 4321 where it could write common log format logs.

There are probably a lot of flaws in the specific syntax here, but I hope you can see past that, to the broader point that the software inside a container has precise expectations of its environment, and that we presently have no way of communicating those expectations beyond writing a Melvilleian essay in each Dockerfile comments, beseeching those who would run the image to give it what it needs.

Why bother with this sort of work, if all the image can do with it is “refuse to run”?

First and foremost, today, the image effectively won’t run. Oh, it’ll start up, and it’ll consume some resources, but it will break when you try to do anything with it. What this metadata will allow the container runtime to do is to tell you why the image didn’t run, and give you specific, actionable, fast feedback about what you need to do in order to fix the problem. You won’t have to go groveling through logs; which is always especially hard if the back-end service you forgot to properly connect to was the log aggregation service. So this will be an order of magnitude speed improvement on initial deployments and development-environment setups for utility containers. Whole applications typically already come with a compose file, of course, but ideally applications would be built out of functioning self-contained pieces and not assembled one custom container at a time.

Secondly, if there were a strong tooling standard for providing this metadata within the image itself, it might become possible for infrastructure service providers (like, ahem, my employer) to automatically detect and satisfy service dependencies. Right now, if you have a database as a service that lives outside the container system in production, but within the container system in development and test, there’s no way for the orchestration layer to say “good news, everyone! you can find the database you need here: ...”.

My main interest is in allowing open source software developers to give service operators exactly what they need, so the upstream developers can get useful bug reports. There’s a constant tension where volunteer software developers find themselves fielding bug reports where someone deployed their code in a weird way, hacked it up to support some strange environment, built a derived container that had all kinds of extra junk in it to support service discovery or logging or somesuch, and so they don’t want to deal with the support load that that generates. Both people in that exchange are behaving reasonably. The developers gave the ops folks a container that runs their software to the best of their abilities. The service vendors made the minimal modifications they needed to have the container become a part of their service fabric. Yet we arrive at a scenario where nobody feels responsible for the resulting artifact.

If we could just say what it is that the container needs in order to really work, in a way which was precise and machine-readable, then it would be clear where the responsibility lies. Service providers could just run the container unmodified, and they’d know very clearly whether or not they’d satisfied its runtime requirements. Open source developers - or even commercial service vendors! - could say very clearly what they expected to be passed in, and when they got bug reports, they’d know exactly how their service should have behaved.

  1. which mostly but not entirely just means “docker”; it’s weird, of course, because there are pieces that docker depends on and tools that build upon docker which are part of this, but docker remains the nexus. 

  2. Yes yes, I know that they’re not really functions Tristan, they’re subroutines, but that’s the word people use for “subroutines” nowadays. 

  3. Just to be clear: no it isn’t. Write a damn docstring, or at least some type annotations