Back-end Engineer in London

We're looking for a Backend Engineer who wants to own, not execute — and build something that genuinely matters to people. If you are excited about independence, impact, and contributing to the wellbeing of employees read on to learn more.

About the role

What you'll work on:

• Own the back-end systems behind everything our team, our clients, and their employees touch — the services that move people's pay.
• Take ownership of back-end services end-to-end — design, build, ship, observe in production, and own what happens next. We run Java 21 and Spring Boot 3 on an event-driven microservices architecture, on AWS, backed by PostgreSQL.
• Build the resilient, secure APIs and async, event-driven workflows that our React Native app, client portals, and back-office all depend on.
• Push back on product and design decisions when the technical tradeoffs aren't understood — and be right often enough that the team listens.
• Make build/buy and now/later calls about a rapidly evolving codebase. Communicate the tradeoffs clearly and own the consequences.
• Treat correctness as the job, not a checkbox. In payroll and payments a wrong number isn't a bug — it's someone's rent. Design for that: real tests (JUnit, Mockito, Testcontainers), observability you'd trust at 2am, and failure modes you've thought through before they happen.
• AI: yes, experimentation, endlessly. We build with Claude Code and others, and expect you to use them as a genuine multiplier on your output.
• Plan from customer feedback and engage in real code review — on both sides of the table.

This is not a feature factory role — engineers at Aslan drive product decisions and own systems end-to-end: design, build, ship, observe, and iterate.

Our stack today:

• Infra: AWS (EC2, RDS, SQS, SNS, SES, Cognito), Docker, GitHub Actions CI/CD
• AI: Claude Code, ChatGPT — we experiment endlessly and expect you to as well

Here are some thoughts on who would be successful in the role:

• Low ego, high standards: You've been wrong before, said so clearly, and moved on. You make the people around you better and leave things in better shape than you found them. The undefined parts of this role excite you more than the defined ones.
• Output over optics: You care about what ships and what works, not what looks good in a standup. No task is beneath you if it unblocks a colleague or serves a user.
• Strong opinions, loosely held: You arrive with a point of view and defend it clearly. But when better information or a better argument comes along, you update without ego. The best idea wins, regardless of who had it.
• Product ownership: You ask "who is the user, what's the job-to-be-done, what's the smallest useful thing we can ship?" You don't wait for perfect specs — you create solutions, communicate tradeoffs, and ship.
• Systems thinking: You notice second-order effects and design for the messy reality — knowing when to move fast and when to slow down.
• Collaboration: You're direct, proactive, and low ego. You give and receive feedback as a gift. No bug is too small if an outcome or colleague depends on it.

One thing this role is not:

If you want a well-defined backlog, clear separation between product and engineering, and a large team to absorb uncertainty, this probably isn't the right fit. If that description sounds limiting rather than comfortable, read on.

Early stage: You have worked in a small & unstructured environment before (ideally a pre-Series C company or a new initiative with high risk in a bigger company). In practice, this means being comfortable in uncertainty and de‑tangling complex customer problems and prioritising features to deliver customer value.

Years of experience: 5 or more. We’re looking for professionals who can structure their own work and be a strong technical voice for the team while getting their hands dirty (we’re not overly strict on exact number of years!).

Industry: Prior experience in fintech is a huge plus.

Technical bar:

• Java & Spring Boot: You've shipped production back-end services, not just prototypes. You know Spring Boot 3 well, write clean code that respects SOLID without turning it into a religion, and have strong opinions about service boundaries, testing, and where complexity belongs.
• Event-driven & async: You're fluent in REST, HTTP, and asynchronous programming, and you design event-driven micro-services that stay correct under failure — not just on the happy path. You know when an event belongs on a queue and when a synchronous call is the honest choice.
• Data & correctness: You design relational schemas that hold up and write complex PostgreSQL queries without reaching for an ORM to hide from them. You understand why correctness matters more than speed in this domain — and you've felt the consequences when it doesn't.
• The integration layer: You're comfortable owning the boundary between back-end and the clients that depend on it — RESTful APIs, event contracts, API-first development. You build services that front-end engineers can trust, and you design for the imperfect callers reality hands you.
• Reliability & observability: You've been paged at 2am. You know what good looks like for error handling, logging, and monitoring, and you build it in from the start rather than bolting it on after the incident. Familiarity with tools like Prometheus and Grafana is a plus.
• Cloud-native: You're at home on AWS (EC2, RDS, SQS, SNS, SES, Cognito), comfortable with Docker and CI/CD via GitHub Actions, and ideally have touched IaC (Terraform) and ECS.
• AI-native development: You use AI tools as a genuine multiplier on your output — not occasionally, but as a core part of how you build and think.
• Fintech context (strong plus): You've worked near payments, ledgers, card processing, or payroll systems. You understand why correctness matters more than speed in this domain, and have felt the consequences when it doesn't.

About Aslan:

Financial wellbeing starts with your job, not your bank. Aslan is a Fintech startup on a mission to revolutionise employee compensation and reward. Aslan is fundamentally changing how people interact with their pay - giving them more of it, with control, freedom and security, seamlessly from payroll. Aslan’s highly engaging product suite covers tax-free rewards, flexible pay options, payroll-embedded savings and budgeting tools. And engage we do… employees use our app and card 30x a month, on average!