Principal Infrastructure Engineer

500M+ downloads. 80M+ monthly users. A decade of building - and we’re still accelerating.

Flo is the world’s #1 health & fitness app worldwide on a mission to build a better future for female health. Backed by a $200M investment led by General Atlantic, we became the first product of our kind to reach a $1B valuation in 2024 - and we’re not slowing down.

With 7M paid subscribers and the highest-rated experience in the App Store’s health category, we’ve spent 10 years earning trust at scale. Now, we’re building the next generation of digital health - AI-powered, privacy-first, clinically backed - to help our users know their body better.

The job

Principal Infrastructure Engineer

More than 80 million women open Flo every month to understand their bodies and their health. Every one of those sessions runs on infrastructure we build, and the data behind it is as personal as data gets. Keeping that fast and private at this scale is the job.

Velocity runs the platform that every Flo engineer builds on: Kubernetes on AWS, the data stores behind our services, and the golden paths that let product teams ship without needing to be infrastructure experts. We treat our internal developers as our customers. You will:

• Own the foundations: Design and run the Kubernetes and data infrastructure behind 80 million monthly active users, and make it boring in the best sense.
• Turn expertise into self-service: Take what you know about running clusters and databases well, and build it into the defaults so product teams get it for free.

What You Will Do

• Kubernetes at scale: Architect and evolve our EKS estate: cluster lifecycle and upgrades, networking, autoscaling, workload isolation, and the Helm and Terraform that deploy onto it.
• Data infrastructure: Shape how our services use PostgreSQL, DynamoDB and Kafka. Set the patterns for provisioning, access, backup, failover and capacity, so teams aren't solving these problems one service at a time.
• Golden paths: Build self-service tooling and Terraform modules that give product teams autonomy without sacrificing stability or security.
• Reliability: Lead resilience work, including business continuity planning, disaster recovery testing and a sustainable on-call rotation.
• Privacy at scale: Support the infrastructure behind privacy features such as our TIME-recognised "Anonymous Mode", and keep us SOC2, ISO 27001 and ISO 27701 certified while handling some of the most sensitive data there is.
• Observability: Make sure metrics, logs and traces tell us something is wrong before our users do.

What You Bring

• Experience: Many years in infrastructure, platform, SRE or DevOps roles running high-traffic, distributed systems in production. You have operated at Principal or Staff scope, setting direction across teams as well as delivering.
• Kubernetes depth: You have run Kubernetes in production for real workloads, ideally EKS. You can explain what happens between kubectl apply and a pod serving traffic, and you have debugged it when it didn't.
• Data infrastructure awareness: You understand how PostgreSQL, DynamoDB and Kafka behave under load and when they fail: connection limits, replication lag, hot partitions, consumer lag, retention. You don't need to have been a DBA, but you know what good looks like and when to ask for help.
• AWS and infrastructure as code: Strong AWS knowledge and fluent Terraform. Coding experience in Go or Python is a plus.
• Communication: A doc-first habit, and the ability to bring distributed product teams with you.

AI first: you will have seen the impact AI automation is having on development teams and the software delivery lifecycle, and have strong ideas on how infrastructure should support it.

Bonus Points

• Hardening infrastructure for high-compliance or security-sensitive environments (HIPAA, SOC 2, PCI).
• Running managed data services in AWS (RDS, Aurora, MSK, DynamoDB) at scale, including migrations and major version upgrades.
• Scaling consumer platforms with millions of concurrent users.
• Certifications such as AWS Certified Solutions Architect Professional, CKA or CKS.

Why Join Flo?

• High impact: Flo is used by 1 in 4 women aged 18-44 in the US, and has raised $200M to build what comes next.
• Autonomy: We hire experts and trust them to deliver.
• Modern stack at scale: EKS, Terraform, Kafka, PostgreSQL, DynamoDB and Sentry, serving more than 80 million people a month.

Annual Salary Range (ranges may vary based on skills and experience)

£130,000—£150,000 GBP

How we work

We’re a mission-led, product-driven team. We move fast, stay focused and take ownership - from brief to build to impact. Debate is encouraged. Decisions are shared. We care about craft, ship with purpose, and always raise the bar.

You’ll be working with people who take their work seriously, not themselves. It takes commitment, resilience, and the drive to keep going when things get tough. Because better health outcomes are worth it. 

What you'll get

We support impact with meaningful reward. Here’s what that looks like:

• Competitive salary and annual reviews
• Opportunity to participate in Flo’s performance incentive scheme
• Paid holiday, sick leave, and female health leave
• Enhanced parental leave and pay for maternity, paternity, same-sex and adoptive parents
• Accelerated professional growth through world-changing work and learning support
• In-person collaboration and work in a hybrid model, with 3 days per week spent in the office
• 5-week fully paid sabbatical at 5-year Floversary
• Flo Premium for friends & family, plus more health, pension and wellbeing perks

Diversity, equity and inclusion

Our strength is in our differences. At Flo, hiring is based on merit, skill and what you bring to the role - nothing else. We’re proud to be an equal opportunity employer, and we welcome applicants from all backgrounds, communities and identities. Read our privacy notice for job applicants.