Rust at CloudFlare

HN: https://news.ycombinator.com/item?id=13718752

The filter expressions are based on the Wireshark Display Filters https://www.wireshark.org/docs/wsug_html_chunked/ChWorkBuild... and we support everything except the slice operator.

Rust handles the parsing, validation, AST creation, etc. That AST can then be applied to a trait table similar to the Wireshark implementation but without the necessity of a pcap step.

I hope that the filter becomes an invariant form of filter against traffic and that once we've got the AST we can apply that filter to different places. Initially just to itself within a Rust matching engine at the edge, but if you have columns on a DB why not ask for a SQL expression derived from the filter expression and then filter a ClickHouse store using the same filter, and likewise as per your suggestion if we can take some of the expressions that aren't L7 why can't we have these run in the network card, etc.

Right now... just CPU as it is early days. But eventually we can look at all places we match traffic and consider that a contender for the same filter to be applied there.

At the moment we have a simple(ish) implementation running at the edge purely within Nginx and a project underway to see how it behaves, gather metrics. That environment gives us a good place in which to control testing, and we can easily compare it to other parts of our code where we already do more trivial request matching (our Page Rules feature).

It'll be a couple of months before we're satisfied we know enough to say whether we'll keep it simple or will seek to make it more specialised to our environment. We haven't yet determined how far we're going to go with this... could it replace our WAF? Is it cheap enough for the DDoS layer? If we do go down those paths then it's obvious that yes we'd move the filtering to other places.

We chose Rust not just for the expected speed and safety but also because we needed to create a shared object that could provide the API (written in Go) with exactly the same parsing and matching engine as our edge (initially Nginx for web traffic written in C and Lua).

The key was to produce consistent behaviour in the way we work with filter expressions such that there is no difference in behaviour that can be leveraged by malicious users later. i.e. if a customer used a filter to create a security rule and that filter behaved even slightly differently later then that would be a security incident in the making and we would have failed our customer.

Rust stood out for being a safer language than C (we had that bug) that could produce a shared object we can use in our API (unlike Lua which does not make this easy), and didn't come with the garbage collection.

We already have some other small bits of Rust in part of our dev pipeline so were comfortable selecting it, but this is the first time we would be shipping Rust globally and running it at the edge.

Our main expectation and hope is performance.

The matching engine that applies the filters is on the hot path for handling requests, it's early in the request lifecycle and all traffic on a zone (customer domain) would need to be evaluated to see whether traffic applies to any existing filter. So the numbers we are looking to gather relate to the time it takes to execute expressions similar to what we have already, as well as more complex expressions, and what this does to CPU load - those two things will dictate how this new project affects the throughput.

The hope is that a more powerful matching engine that is fast and doesn't increase CPU load will allow us to remove code from our system whilst providing customers with fine grained control of all features. Today a lot of features implement their own matching on paths, headers, etc... and these are not always efficient and are implemented inconsistently.

Performance is therefore what we are focused on measuring and improving, and we hope that if the numbers are good Rust will provide us the opportunity to remove other code and increase throughput whilst not giving us fear that such a change has opened us up to other more fundamental risks.

Right, but this is talking about GLOBAL capacity, not at a single datacenter. The CDN I work for has over 49tbps, and we wouldn't claim to be doing 10% of all HTTP traffic:

https://images.verizondigitalmedia.com/2015/12/VDMS_NetworkM...

Plus, capacity is always going to be greater than actual throughput, both for reliability reasons and traffic patterns (i.e. you need enough capacity for your peak traffic in a datacenter, not the average)

I really doubt the 10% claim.