# Hyperice: Backend rewrite for the HyperSmart app, four weeks before launch

URL: https://extra.dev/work/hyperice
Year: 2023 · Services: web, devops, qa, ai-ml
Industry: Connected devices & recovery technology
Engagement: Teams
Scope: Backend rewrite, migration, infrastructure, integrations, AI
Timeline: From 2023, 4 weeks to launch

**Replacing the Hyperice backend four weeks before launch**

Hyperice’s HyperSmart app connects recovery devices with guided routines, activity data and personalised recommendations. Four weeks before launch, we took over its backend, rewrote it and launched on the original date, then kept building the product.

Results: 4 weeks From backend takeover to launch (On the original date, with no downtime during the migration); 25,000+ Concurrent users supported at launch (During the launch window, at 99.8% uptime); 77% Lower database response time (From 1,200ms to 280ms).

## Four weeks to replace a backend that could not scale

HyperSmart connects Hyperice’s recovery devices with guided routines, activity data and personalised recommendations. Its backend runs the accounts, integrations and recommendations behind the app.
We took the backend over four weeks before launch. Database queries were slow, the code had no coherent structure, the system crashed, and the architecture could not carry the traffic expected at launch. It also held the accounts of people already using an earlier Hyperice app.
Patching it would have kept the structure that caused those problems. We chose a full rewrite, delivered for the original launch date.

## A new backend, and a migration users never saw

We rewrote the backend and the REST APIs behind the app and web clients in NestJS. The data model and indexes were redesigned around the queries the app actually made, with caching in Redis, and database response times fell from 1,200ms to 280ms.
Before go-live, k6 load tests modelled launch traffic against staging. The AWS infrastructure was defined in Terraform, with monitoring, alerting and runbooks in place for launch day.
The hardest part was the switch itself. Users of the earlier app had to move to the new backend without noticing. Both backends accepted the same session tokens, so anyone signed in on the old one stayed signed in on the new one. The switch took no downtime and signed nobody out.

## An on-time launch, then product development

HyperSmart launched on its original date. During the launch window the new backend carried more than 25,000 concurrent users at 99.8% uptime.
After launch we stayed on to build the product: integrations with Apple Health, Android Health, Strava, Garmin and Whoop, then AI longevity scoring and recovery recommendations delivered through notifications. The app has since grown to hundreds of thousands of monthly active users.

Delivered: Full backend rewrite and REST APIs for the app and web clients; Data model, indexes and caching redesigned around real queries; User migration on shared session tokens: no downtime, no sign-outs; k6 load testing against expected launch traffic; AWS infrastructure in Terraform for staging and production; Monitoring, alerting and runbooks for launch and operations; Integrations with Apple Health, Android Health, Strava, Garmin and Whoop; AI longevity scoring and recovery recommendations via notifications.
Built with: Back-end: NestJS, TypeScript, REST APIs · Data: PostgreSQL, Redis · Platform: AWS, Firebase, CircleCI, Docker, Terraform · Reliability: k6, Grafana.

> "They took over our backend a month before launch and still shipped on time. I haven’t seen a team move that fast without breaking things. Concurrency went from a worry to a footnote, 25,000+ users at launch and the database never blinked." (Daniel K., CTO, recovery-tech brand)

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Published by Extra.dev (https://extra.dev), a software engineering team in Ljubljana, Slovenia.
Canonical page: https://extra.dev/work/hyperice
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