Cloudflare’s Gen X: Servers for an Accelerated Future
“Every server can run every service.”
We designed and built Cloudflare’s network to be able to grow capacity quickly and inexpensively; to allow every server, in every city, to run every service; and to allow us to shift customers and traffic across our network efficiently. We deploy standard, commodity hardware, and our product developers and customers do not need to worry about the underlying servers. Our software automatically manages the deployment and execution of our developers’ code and our customers’ code across our network. Since we manage the execution and prioritization of code running across our network, we are both able to optimize the performance of our highest tier customers and effectively leverage idle capacity across our network.
An alternative approach might have been to run several fragmented networks with specialized servers designed to run specific features, such as the Firewall, DDoS protection or Workers. However, we believe that approach would have resulted in wasted idle resources and given us less flexibility to build new software or adopt the newest available hardware. And a single optimization target means we can provide security and performance at the same time.
We use Anycast to route a web request to the nearest Cloudflare data center (from among 200 cities), improving performance and maximizing the surface area to fight attacks.
Once a datacenter is selected, we use Unimog, Cloudflare’s custom load balancing system, to dynamically balance requests across diverse generations of servers. We load balance at different layers: between cities, between physical deployments located across a city, between external Internet ports, between internal cables, between servers, and even between logical CPU threads within a server.
As demand grows, we can scale out by simply adding new servers, points of presence (PoPs), or cities to the global pool of available resources. If any server component has a hardware failure, it is gracefully de-prioritized or removed from the pool, to be batch repaired by our operations team. This architecture has enabled us to have no dedicated Cloudflare staff at any of the 200 cities, instead relying on help for infrequent physical tasks from the ISPs (or data centers) hosting our equipment.
Gen X: Intel Not Inside
We recently turned up our tenth generation of servers, “Gen X”, already deployed across major US cities, and in the process of being shipped worldwide. Compared with our prior server (Gen 9), it processes as much as 36% more requests while costing substantially less. Additionally, it enables a ~50% decrease in L3 cache miss rate and up to 50% decrease in NGINX p99 latency, powered by a CPU rated at 25% lower TDP (thermal design power) per core.
Notably, for the first time, Intel is not inside. We are not using their hardware for any major server components such as the CPU, board, memory, storage, network interface card (or any type of accelerator). Given how critical Intel is to our industry, this would until recently have been unimaginable, and is in contrast with prior generations which made extensive use of their hardware.
Intel-based Gen 9 server
This time, AMD is inside.
We were particularly impressed by the 2nd Gen AMD EPYC processors because they proved to be far more efficient for our customers’ workloads. Since the pendulum of technology leadership swings back and forth between providers, we wouldn’t be surprised if that changes over time. However, we were happy to adapt quickly to the components that made the most sense for us.
CPU efficiency is very important to our server design. Since we have a compute-heavy workload, our servers are typically limited by the CPU before other components. Cloudflare’s software stack scales quite well with additional cores. So, we care more about core-count and power-efficiency than dimensions such as clock speed.
We selected the AMD EPYC 7642 processor in a single-socket configuration for Gen X. This CPU has 48-cores (96 threads), a base clock speed of 2.4 GHz, and an L3 cache of 256 MB. While the rated power (225W) may seem high, it is lower than the combined TDP in our Gen 9 servers and we preferred the performance of this CPU over lower power variants. Despite AMD offering a higher core count option with 64-cores, the performance gains for our software stack and usage weren’t compelling enough.
We have deployed the AMD EPYC 7642 in half a dozen Cloudflare data centers; it is considerably more powerful than a dual-socket pair of high-core count Intel processors (Skylake as well as Cascade Lake) we used in the last generation.
Readers of our blog might remember our excitement around ARM processors. We even ported the entirety of our software stack to run on ARM, just as it does with x86, and have been maintaining that ever since even though it calls for slightly more work for our software engineering teams. We did this leading up to the launch of Qualcomm’s Centriq server CPU, which eventually got shuttered. While none of the off-the-shelf ARM CPUs available this moment are interesting to us, we remain optimistic about high core count offerings launching in 2020 and beyond, and look forward to a day when our servers are a mix of x86 (Intel and AMD) and ARM.
We aim to replace servers when the efficiency gains enabled by new equipment outweigh their cost.
The performance we’ve seen from the AMD EPYC 7642 processor has encouraged us to accelerate replacement of multiple generations of Intel-based servers.
Compute is our largest investment in a server. Our heaviest workloads, from the Firewall to Workers (our serverless offering), often require more compute than other server resources. Also, the average size in kilobytes of a web request across our network tends to be small, influenced in part by the relative popularity of APIs and mobile applications. Our approach to server design is very different than traditional content delivery networks engineered to deliver large object video libraries, for whom servers focused on storage might make more sense, and re-architecting to offer serverless is prohibitively capital intensive.
Our Gen X server is intentionally designed with an “empty” PCIe slot for a potential add on card, if it can perform some functions more efficiently than the primary CPU. Would that be a GPU, FPGA, SmartNIC, custom ASIC, TPU or something else? We’re intrigued to explore the possibilities.
In accompanying blog posts over the next few days, our hardware engineers will describe how AMD 7642 performed against the benchmarks we care about. We are thankful for their hard work.
Memory, Storage & Network
Since we are typically limited by CPU, Gen X represented an opportunity to grow components such as RAM and SSD more slowly than compute.
For memory, we continued to use 256GB of RAM, as in our prior generation, but rated higher at 2933MHz. For storage, we continue to have ~3TB, but moved to 3x1TB form factor using NVME flash (instead of SATA) with increased available IOPS and higher endurance, which enables full disk encryption using LUKS without penalty. For the network card, we continue to use Mellanox 2x25G NIC.
We moved from our multi-node chassis back to a simple 1U form factor, designed to be lighter and less error prone during operational work at the data center. We also added multiple new ODM partners to diversify how we manufacture our equipment and to take advantage of additional global warehousing.
Our newest generation of servers give us the flexibility to continue to build out our network even closer to every user on Earth. We’re proud of the hard work from across engineering teams on Gen X, and are grateful for the support of our partners. Be on the lookout for more blogs about these servers in the coming days.