This past weekend, I and several others made our way to ULB for FOSDEM 2014. FOSDEM is an annual conference aimed at the free and open source software communities. In addition to talks on a wide variety of topics, it doubles as a convenient place and time for developers on projects who are spread all over the world to meet up in person.

I attended a bunch of talks over the weekend; below is a brief list and some impressions based on my recollections and notes. Almost all the talks were recorded; once they’ve been published, I’ll come back to this blog and link them all.


Reproducible Builds in Debian

Binary packages in Debian are currently the opposite of reproducible. Two consecutive builds of the same source package on the same machine will produce different binaries. Most differences come from timestamps (in archive formats, documentation, etc) but there are some other sources. There is an effort on going at the moment to modify the tooling used to create binary packages in Debian to eliminate these sources of variation. An experiment using these modified build tools resulted in more than 60% of packages being identical. That’s insanely impressive. It seems very possible that we could get to a situation where 100% of packages are verifiable. If we could then create an audited build image from first principles (or ideally two or three), it would become significantly harder for an attacker to sneak undocumented behaviour into these packages. Definitely one to watch.

Autoscaling Best Practices

A talk about autoscaling; what it is in general, the various types of autoscaling, what it’s good at, what it’s not so good at, and some of the implementations available in the world. A solid high level overview which gives good advice. Worth watching if you’re new to the concept of autoscaling infrastructure. (TODO: video).

Network Function Virtualisation and Network Service Insertion and Chaining

This was a somewhat theoretical talk about how the world changes when you virtualise network services, using the various components of OpenStack to provide examples.

Briefly: a network service is some capability which is provided by the network to one or more application/host/hypervisor. The most trivial network service is that of basic connectivity; the ability to send packets elsewhere, although obviously this isn’t that interesting.

Consider instead something a little more complex; say a network firewall, or a load balancer. Traditionally these capabilities/services have been provided by big centralised pieces of Magic Vendor Hardware; having a pair of firewalls and a pair of load balancers for an entire datacenter is a fairly common (anti?) pattern. This leads to a bunch of complexity and scaling issues.

For example: if you need to firewall flows between two applications in your cluster, you need to drag those flows all the way up to your firewalls and then back down again, even if the applications are running on two VMs/containers scheduled on the same hypervisor. This then has implications for how much bandwidth you need to provision from your top of rack switches to your cluster edge and back. Your firewall policy also grows alarmingly; it is essentially the union of all permitted flows to/from every node in your cluster. Such a policy is going to become difficult to maintain and reason about, and quite possibly is going to blow out the capacity of whatever BigCorp firewall appliance you’re using, meaning that you soon have to start scaling it out.

A key point this talk makes, which bears emphasising: you don’t need SDN for virtualised network services, but the two do complement each other nicely.

Now, let’s pretend that this is a world where network functions are virtualised, and that I’m spinning up a new SSL web service.

I need a new public IP, because SSL; no problem, my SDN control plane starts advertising the new IP via BGP to the outside world, and my SDN controller installs a flow on my edge routers which sends any traffic to this new IP to some newly provisioned software load balancer instance which is running inside the cluster. It also updates the iptables rules on the hypervisor that the loadbalancer is running on, permitting inbound port 443 traffic to the new public IP.

In the mean time, my cluster control infrastructure has spun up a reverse proxy VM as well as a webserver on which I can run the actual website. Right now, because no-one knows about this service, the load balancer, the reverse proxy, and the web server VMs are all running on the same hypervisor. However, 6 months from now, when people actually care about this service, scaling it out is a simple case of spinning up more instances of whatever the bottleneck component is, combined with possibly updating some flow rules so that you can have more than one load balancer.

Compare this to a world where you need to submit tickets for new hardware, new firewall rules, some load balancer changes, some reverse proxy changes… a new order is coming, folks. Adapt or die.

Dovecot’s way of scaling to millions of users

This was an interesting talk by Dovecot’s maintainer about the various implementation optimisations that have been made in order to get over performance limitations in Dovecot. There was some interesting conceptual/philosophical stuff here (e.g. everything should be asynchronous), as well as good discussion about the architecture of a scaled Dovecot installation. (Leaf nodes, proxies, directors). I’m reasonably certain that I’m going to have to get back to self-hosting my own mail in the next few years, as Gmail becomes more and more of a consumer product, so this was a useful refresher on how real email works.

SPARK 2014: Hybrid Verification using Proofs and Tests

An interesting talk on how to extend compiler and testing infrastructure. A lot of it went over my head, since I don’t spend enough time coding, but the main thrust of this seemed to be that contracts (decorators/hints to the compiler which express preconditions/postconditions/invariants) allow you to move many runtime assertion/check failures to compile time. (Trivial example; bounds checking on array access). In addition, contracts allow you to skip a vast swathes of trivial unit tests; e.g. the contract for an “increment” function provides sufficient information to allow the compiler to auto-generate test cases; we shouldn’t need to write them ourselves.

SPARK appears to include a bunch of interesting language constructs which aid in producing safer, less fragile code. It will be interesting to see if contracts or something like them make their way into more widely used languages.


Not a talk, rather a project I found out about.

Foreman is an opensource project for managing the lifecycle of physical and virtual servers, from provisioning to operating to monitoring to configuring to decommissioning. It looks like a mature project, with significant support for both Puppet and Chef, as well as a bunch of physical and cloud compute providers. Definitely a project to keep an eye on.

Who ate my battery?

Why free and open systems are solving the problem of excessive energy consumption.

This was a very thought provoking talk about the seeming disconnect between the hardware and software worlds when it comes to power optimisation. The hardware world has long included “power consumption” as one of the variables in the optimisation problems that are being solved. In the “old” days, when embedded hardware ran custom, purpose written software, such hardware features were made use of as a matter of course. Now, more and more embedded devices run general purpose operating systems and applications written in high level languages which do not expose developers to the realities of embedded development. This has a direct impact on the power efficiency of such devices.

This talk discussed various approaches to change this; starting with the profiling of software combined with measuring power consumption, in order to gather power efficiency data for various combinations of hardware, compiler, compiler version, compiler optimisations… and so on. Once this profiling data has been gathered, it can then be used to feed a machine learning system which then generates a model with which to simulate upper and lower bounds for power consumption of various algorithms/implementations of those algorithms, given a set of the above constraints. Think of these as akin to back of the napkin calculations based on latency numbers every progammer should know.

The end goal is to extend general purpose compilers like GCC and CLANG to provide -o power optimisation modes, to produce binaries that run efficiently in power constrained environments. The project as a whole is called MAGEEC, and it looks very promising.

The FOSDEM Network

FOSDEM is a unique environment; thousands of geeks descend on the ULB campus every year to talk about all manner of interesting topics. There are no fees, and no guest registration. Running a wireless network in such an environment might be described as challenging. Only a crazy person would make it harder by making the wireless network IPv6 only by default.

Running a v6 only network by default isn’t something that’s really been done at scale before, as far as I’m aware. Networking events like IETF and NANOG have had an IPv6 only SSID for a while, but those events self-select for people who know about IPv6. FOSDEM, in contrast, is an event aimed at the open source community, most of whom don’t care about IPv6. Setting the default SSID to be IPv6 only, with transition mechanisms in place to facilitate access to the legacy IPv4 internet was a bold move; the good news is that it seems to have gone extremely well. (Modulo a bug which meant every Android user had to switch to the fallback FOSDEM-dualstack SSID. Boo!). Also, it broke anyone validating DNSSEC; which Faux, tom and I spent far too much time discussing.

In addition to talking about how this was done, there were some interesting stats about the number of unique devices, how much traffic FOSDEM sees, etc. All in all very interesting (but then again, I am a network geek).

Preventing craziness: a deep dive into OpenStack testing automation

For those who aren’t aware, OpenStack is an “open source cloud operating system”; it’s a collection of subprojects which, when taken together, allow you to spin up your own private cloud on top of computer, networking and storage resources.

This was a really impressive talk. Openstack is 2 million source lines of code spread across 95+ code repositories, with 400 contributors, all of whom can commit changes. In order to keep control over the chaos that results, the people responsible for OpenStack’s project infrastructure have put together an impressive set of processes and controls which allows them to cut a release every 6 months and to have a master branch which is always usable despite dozens of merges a day. I have reams of notes but the TL;DR is:

  • Nothing gets merged without being code reviewed by two other people.
  • Nothing gets to code review without tests passing.
  • If something is not tested automatically, it’s not tested.
  • If something is not tested, it doesn’t work.

Though I have reams of notes from this talk, I’m not going to replicate them here. Instead, I highly recommend watching the talk when it’s published; this is how to do rapid software development at scale, and the OpenStack team have either integrated or created a bunch of open source tools to make it work really well. This project has always intrigued me; now that I’ve seen how they run things, I’m even more convinced that they’re going to end up being the default open source cloud management solution.

ANSTE: Advanced Network Service Testing Environment

Testing Network Services in Multimachine Scenarios

This was a lightning talk on a framework for testing network services using a bunch of virtual machines. I don’t have reams of notes, but it did seem to be fairly straightforward to use, and provided a simple way for developers to spin up and configure interconnected VMs for the purposes of testing network applications.

Adventures with CloudStack and OpenDaylight

A talk about getting support for OpenDaylight into the CloudStack project. Some background:

OpenDaylight is an open source software defined networking (SDN) platform. What is SDN? It’s a topic for another blog post, but the short version is: a network which is configured by software applications written by your own developers, rather than by software provided by your network hardware vendor.

CloudStack is similar to OpenStack; it’s an open source cloud management platform.

This talk chronicled the experience of one of the CloudStack developers in getting support for provisioning networking for VMs OpenDaylight into OpenStack. It was quite interesting, but did serve to demonstrate that OpenDaylight still has quite a ways to go before it’s production ready.

Tunnels as a Connectivity and Segregation Solution for Virtualized Networks

This was an excellent talk, in my opinion. It’s targeted at developers who don’t have much/any understanding of networking below the sockets API.

It sought to explain the importance of tunnelling in network solutions for VM-VM communication in a virtualised environment. It started with some historical background about how Ethernet works, and why VLANs are the hammer of choice for many network engineers when it comes to segregation. It then went on to explain that in a world where networking is moving up into the hypervisor, VLANs aren’t necessarily the best choice for this anymore.

Overall an excellent explanation of how networking works in today’s virtualised datacenters; stuff that every developer should know. I’ve given variants of this talk at employers; it’s good to see this stuff being discussed in the wider open source community.

No more IPv4

A talk by IPv6 evangelist Eric Vyncke about the implication of IPv4 exhaustion; the nature of an internet with ever-increasing amounts of NAT, and how applications can be extended with relatively little work to support IPv6. Specifically, why should open source developers care about IPv6? Because sooner or later, some of their customers will only have IPv6 connectivity, or horribly broken, multiply NATted IPv4 connectivity.

As an aside: I was pleasantly surprised at the focus that IPv6 received at FOSDEM this year; both this and the earlier talk about the FOSDEM network were in large rooms and pretty full. Hopefully this reflects a growing interest in IPv6 from the wider open source community.

Using RIPE Atlas API for measuring IPv6 Reachability

RIPE-NCC is the organisation responsible for distributing number resource (IPv4, IPv6 addresses, AS numbers) to the European internet community. In addition to this primary responsibility, they also provide a bunch of data and tools to the internet community, to assist service providers with monitoring and analysing the internet. One of those tools is ATLAS, a distributed system managed by RIPE NCC used for running large scale measurement across the internet.

ATLAS is made up of a bunch of probes which run a stripped down, hardened Linux distribution which are installed in host networks around the world. These probes are then used by RIPE NCC (and members who sign up to use the API) to run tests about internet reachability from devices all over the world. The data from such tests is then made freely available to the internet community. The source code for the probes is freely available.

This talk provided some detail about what RIPE NCC and ATLAS are, and how to use ATLAS to get information about IPv6 reachability on the internet. It was very interesting; ATLAS itself seems like a very cool project; I’ve requested a probe for myself, and will probably sponsor a few more once I get one.

NSA operation ORCHESTRA: Annual Status Report

I can’t do this one justice; once the video is published, you just have to go and watch it. :)


Wow. That’s the longest blog I’ve written in a while. I may expand on some of the talks/topics raised in future blog posts; I’m definitely going to continue attending FOSDEM. The fact that such an event can be set up for free and attract 5000+ developers from all over the world continues to amaze me. See everyone next year!

(To come: my write up of Configuration Management Camp, which occurred down the road in Hogent immediately following FOSDEM).