Freelance Backend Engineer · Kotlin · Java · AWS

Backends that stay calm under load.

I build Kotlin and Java backends on AWS – AI-assisted for speed, human for architecture, review and accountability. With more than 15 years of experience.

Book an intro call See success stories

OrderEvents.kt

// Large payloads? They go to S3 automatically.
val extendedClient =
    SqsExtendedClient(
        sqsClient,
        SqsExtendedClientConfig(
            payloadStore = S3BackedPayloadStore(
                s3Client,
                bucketName = "order-payloads",
            ),
        ),
    )

extendedClient.sendMessage(SendMessageRequest {
    queueUrl = ordersQueue
    messageBody = largePayload
})

sqsoverflow · Open SourceMaven Central

15+: years of backend experience
Kotlin & Java: at home on the JVM
AWS: SQS, SNS, S3 and more
3 Libraries: open source on Maven Central

01 — Services

From first draft to stable operation.

I step in wherever your team needs support – as developer, architect or both.

Backend development

Robust services in Kotlin and Java: clean APIs, well-designed data models, tests that actually protect something.

→ New services & APIs
→ Java-to-Kotlin modernization
→ Test automation

AWS architecture

Event-driven systems that scale and stay affordable – with messaging, storage and infrastructure as code.

→ SQS, SNS & S3
→ Event-driven Architecture
→ Architecture reviews

AI-assisted development

I use AI where it adds speed – and keep architecture, code review and accountability firmly in my own hands.

→ Faster to working software
→ Every line reviewed by a human
→ AI workflows for your team

All services in detail →

02 — How I work

AI for speed. A human for accountability.

01
Intro call
We clarify goals, starting point and scope – concrete and without obligation.
02
Analysis & architecture
I review code and infrastructure and propose a clear path forward.
03
Delivery
In short iterations, with visible results and thorough review.
04
Handover
Documented and easy to follow, so your team can carry on independently.

03 — Open Source

Code you can inspect before you hire me.

All projects on GitHub

Extended clients for aws-sdk-kotlin: they automatically offload large SQS and SNS messages to S3 – derived from the AWS Java libraries, built for Kotlin and coroutines.

com.christoph-sens

s3overflow

The foundation: an S3 payload store the other clients build on.

com.christoph-sens

sqsoverflow

Extended client for Amazon SQS – messages above the size limit go to S3 transparently.

com.christoph-sens

snsoverflow

Extended client for Amazon SNS – combine it with sqsoverflow for fan-out scenarios.

04 — Success Stories

Results from real projects.

All success stories (German)

Kotlin · AWS · Open Source

Extended clients for Kotlin – closing a gap in the AWS ecosystem

AWS offers extended clients for large SQS and SNS messages for Java only. The Kotlin counterpart: around 730 lines instead of thousands, no Jackson, tested and on Maven Central.

PDF generation in microservice landscapes

A microservice renders multilingual PDFs from HTML templates. Templates and translations can be swapped without a deployment – using license-friendly building blocks such as OpenPDF and Noto.

Backends that stay calm under load.

From first draft to stable operation.

Backend development

AWS architecture

AI-assisted development

AI for speed. A human for accountability.

Intro call

Analysis & architecture

Delivery

Handover

Code you can inspect before you hire me.

s3overflow

sqsoverflow

snsoverflow

Results from real projects.

Extended clients for Kotlin – closing a gap in the AWS ecosystem

PDF generation in microservice landscapes

Let’s talk about your backend.