Floci: a free, open-source LocalStack alternative

A binary that boots in 24 milliseconds, needs no token, needs no cloud account, and emulates most of AWS on your laptop. That's the pitch behind Floci, a project that just cracked 150 points on Hacker News after developers noticed it fills exactly the gap LocalStack left open.

What happened

Floci is a family of open-source cloud emulators, MIT-licensed, compiled to native binaries with Quarkus and GraalVM Mandrel. Each provider ships as its own binary and container, listening on a fixed port:

Provider	Repo	Port	Services
AWS	floci	4566	119
Azure	floci-az	4577	28
GCP	floci-gcp	4588	25
OCI	floci-oci	4599	8

The AWS build uses port 4566 — the same as LocalStack — so teams can swap endpoints without touching a line of code. The AWS service list covers S3, SQS, DynamoDB, Lambda, RDS, ElastiCache, EKS, and over a hundred more, checked against a dedicated compatibility test suite on GitHub.

What made this spread on Hacker News wasn't the tech itself — it was the backstory. LocalStack, the tool most teams have relied on for years to emulate AWS locally, started requiring an auth token in March 2026, pushing some features behind a paid tier. For a team that just needs S3 and SQS to run tests, that's friction nobody asked for.

Why now

Floci isn't the first tool to challenge LocalStack. But it lands at the intersection of two trends running in parallel. One is mature open-source tools tightening licenses to chase revenue (this blog covered GitLab.com's new rate limits just last week). The other is a wave of AI coding agents that need a safe sandbox to try, fail, and retry without supervision.

Floci's landing page addresses that second group directly. Agents write cloud infrastructure code fast, but can't safely run it against a real AWS account — the risk is either a surprise bill or leaked credentials. Floci sidesteps both: agents connect with throwaway keys, there's nothing to exfiltrate and nothing to bill, and if an agent breaks the container, the fix is docker restart.

One striking comment on the HN thread: a real user says a specific Floci feature was built over a single weekend using a $20/month Claude plan, and the community picked up the rest from there. In other words, the project itself is a case study of AI lowering the barrier to bootstrap core dev infrastructure — a theme this series has revisited repeatedly, from the Bun Rust rewrite to DuckDB's evolution.

What's actually different from LocalStack

• Native binaries: built with GraalVM Mandrel instead of running on a standard JVM, giving a 24ms cold start and 13MiB idle memory — a meaningful jump over spinning up a JVM-based LocalStack container.
• Real engines, not mocks: Lambda runs in real Docker containers, RDS uses real PostgreSQL/MySQL, ElastiCache runs real Redis. That's a real distinction from mocks that just return canned responses — tests passing against Floci carry more signal about production behavior.
• No auth token, no feature gates: all 119 AWS services stay free indefinitely per the maintainer's stated commitment, funded through GitHub Sponsors rather than paid licenses.

The catch

Not every team should switch tomorrow. One especially sharp comment on the thread argues that if your architecture already abstracts the cloud vendor cleanly, most of your code never needs to touch the real cloud in tests. You only need to validate that abstraction layer against the real thing, which is cheap enough to do directly. Production-like end-to-end tests should still run against real infrastructure, not an emulator. Floci is strongest for the inner loop: writing code, testing quickly while coding, running ephemeral CI jobs — not as a full replacement for a staging environment.

Worth noting too: the project is still young, and Malwarebytes has flagged floci.io as potentially unsafe at times — a common false positive for newer domains, but something teams should verify before wiring it into public CI pipelines.

What this means for developers

• If your team is paying for LocalStack or hitting its feature limits, Floci is a viable drop-in for most basic S3/SQS/DynamoDB/Lambda workloads, no endpoint changes required.
• Teams letting AI coding agents run infrastructure code unsupervised should consider a local cloud emulator like this as the default sandbox, instead of handing over real keys or relying entirely on static mocks.
• Before ripping out LocalStack from CI entirely, benchmark compatibility against the exact services your project uses — 119 emulated services doesn't guarantee every edge case behaves identically.

Floci is still young compared to a decade of LocalStack. But the fact that a tool mostly written by AI over a few weekends is already good enough to top Hacker News says something about how low the barrier has gotten for rebuilding core dev infrastructure from scratch.

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Content assisted by AI (Amy 🌸). Reviewed by the author.