Software Engineer, DDoS

Cloudflare, London, UK

Help us build a better Internet

About Us

At Cloudflare, we have our eyes set on an ambitious goal: to help build a better Internet. Today the company runs one of the world’s largest networks that powers approximately 25 million Internet properties, for customers ranging from individual bloggers to SMBs to Fortune 500 companies. Cloudflare protects and accelerates any Internet application online without adding hardware, installing software, or changing a line of code. Internet properties powered by Cloudflare all have web traffic routed through its intelligent global network, which gets smarter with every request. As a result, they see significant improvement in performance and a decrease in spam and other attacks. Cloudflare was named to Entrepreneur Magazine’s Top Company Cultures list and ranked among the World’s Most Innovative Companies by Fast Company. 

We realize people do not fit into neat boxes. We are looking for curious and empathetic individuals who are committed to developing themselves and learning new skills, and we are ready to help you do that. We cannot complete our mission without building a diverse and inclusive team. We hire the best people based on an evaluation of their potential and support them throughout their time at Cloudflare. Come join us! 

About the team

The DDoS Protection team creates software that stops some of the largest DDoS attacks in the world. Our team is split evenly across Austin, TX USA and London, UK and this position is for the London location. Our software is written in Rust, Go, Python, and Lua. Our data pipeline uses Kafka, PostgreSQL and ClickHouse. Our software is run within Kubernetes or on Debian Linux. We monitor using Prometheus, Kibana, and Grafana.

DDoS mitigation systems are super reactive, analysing the global and local edge traffic to the tune of 2.8 million requests per second to build a holistic picture of traffic and identify different attacks and floods. Once detected it emplaces rules that mitigate the impact within seconds.

The DoS team is responsible for ensuring that customers and Cloudflare own edge centers are always protected from DDoS attacks. Prime responsibilities will be to be ahead of the curve to detect and mitigate attacks as they evolve over time.Your work will have a real impact protecting Cloudflare infrastructure and customer websites across every vertical and country.

About the role

We are looking for engineers with some knowledge of networking stack and distributed systems. At Cloudflare we have seen one of the largest internet attacks crossing millions of requests/packets per second. You will be responsible for building and enhancing software that protects millions of websites from these denial-of-service attacks.

The work will focus on evolving DoS systems that are distributed across data centers and protect against different types of attacks. You will contribute to shaping future systems along with building and evolving complex systems. With such a large scale system we have a huge data footprint and part of the work will be focussed on building insights from that data to better protect against attacks.

You are ideally self-motivated, creative, and take pride in shipping well-crafted, maintainable code.


  • Build new software features to improve our DDoS protections, evolve our systems to be ready for tomorrow.
  • Leading projects as an engineer, that expand our DDoS protections
  • Analysing data to identify patterns and strengthening our existing systems.
  • Monitoring and analysing logs and metrics to ensure system health
  • Working on tooling and support around our software
  • Communicating via internal and public channels about what we do, why, and how we do it
  • Handle escalations from Support or SREs, which may include out of hour support in rare cases

Examples of desirable skills and experience:

We do not require you to have all of these and a degree is not required for this role.

  • Experience working with high scale distributed systems
  • Experience with Rust, or Go
    • Or similar and with a willingness to learn Rust and Go
  • Knowledge of core protocols for the web (TCP/IP, HTTP, HTTP/2, TLS, QUIC)
  • Experience building and designing APIs
  • Experience querying databases using SQL and a bonus if you have experience with big data technologies.
  • Awareness of linux stack is a bonus
  • Awareness of common types of web application vulnerabilities
  • Awareness of common web application software (Wordpress, Drupal, Magento, etc)
  • Talent for discovering anomalies in data

What Makes Cloudflare Special?

We’re not just a highly ambitious, large-scale technology company. We’re a highly ambitious, large-scale technology company with a soul. Fundamental to our mission to help build a better Internet is protecting the free and open Internet.

Project Galileo: We equip politically and artistically important organizations and journalists with powerful tools to defend themselves against attacks that would otherwise censor their work, technology already used by Cloudflare’s enterprise customers--at no cost.

Athenian Project: We created Athenian Project to ensure that state and local governments have the highest level of protection and reliability for free, so that their constituents have access to election information and voter registration.

Path Forward Partnership: Since 2016, we have partnered with Path Forward, a nonprofit organization, to create 16-week positions for mid-career professionals who want to get back to the workplace after taking time off to care for a child, parent, or loved one. We released to help fix the foundation of the Internet by building a faster, more secure and privacy-centric public DNS resolver. This is available publicly for everyone to use - it is the first consumer-focused service Cloudflare has ever released. Here’s the deal - we don’t store client IP addresses never, ever. We will continue to abide by our privacy commitment and ensure that no user data is sold to advertisers or used to target consumers.

Sound like something you’d like to be a part of? We’d love to hear from you!

This position may require access to information protected under U.S. export control laws, including the U.S. Export Administration Regulations. Please note that any offer of employment may be conditioned on your authorization to receive software or technology controlled under these U.S. export laws without sponsorship for an export license.

Cloudflare is proud to be an equal opportunity employer.  We are committed to providing equal employment opportunity for all people and place great value in both diversity and inclusiveness.  All qualified applicants will be considered for employment without regard to their, or any other person's, perceived or actual race, color, religion, sex, gender, gender identity, gender expression, sexual orientation, national origin, ancestry, citizenship, age, physical or mental disability, medical condition, family care status, or any other basis protected by law. We are an AA/Veterans/Disabled Employer.

Cloudflare provides reasonable accommodations to qualified individuals with disabilities.  Please tell us if you require a reasonable accommodation to apply for a job. Examples of reasonable accommodations include, but are not limited to, changing the application process, providing documents in an alternate format, using a sign language interpreter, or using specialized equipment.  If you require a reasonable accommodation to apply for a job, please contact us via e-mail at [email protected] or via mail at 101 Townsend St. San Francisco, CA 94107.

About Cloudflare

About us

Cloudflare is the simplest way to make websites faster, safer and smarter. Millions of websites have signed up for our service, including large enterprises, major consumer destinations, and government agencies. With offices in San Francisco and London, Cloudflare operates a highly-available global network that has security measures built into every layer and regularly clocks in lightning-fast speeds.

We're on a mission to build a better web - and we need smart, talented people to join our team. Our team works on the forefront of leading technologies including nginx, Go and Lua programming languages. We're a strong supporter of the open source community and regularly share our technology learnings at https://blog.cloudflare.com.

Want to learn more about Cloudflare? Visit Cloudflare's website.