Floci: free open-source LocalStack alternative runs AWS services locally in Docker

A gap opened in local AWS development

LocalStack, a widely used tool for emulating AWS services on a developer's machine, retired its open-source Community edition earlier this year. According to dev.to, the project shipped version 2026.03.0 on March 23, 2026, archived its GitHub repositories, and consolidated everything into a single Docker image that will not start without an auth token tied to a registered account. A temporary bypass via an environment variable expired on April 6, 2026.

The source code for the old Community image remains archived up to v4.14.0, but dev.to reports it no longer receives security updates. A free Hobby plan still exists for non-commercial use, while commercial licences reportedly start at $39 per month. For teams that simply wanted S3 and Lambda on localhost without strings attached, that change prompted a search for alternatives — and Floci is the project that positioned itself directly in the gap.

What Floci does

Floci is a free, MIT-licensed AWS emulator that runs as a single Docker container listening on port 4566 — the same port LocalStack uses. The AWS CLI, official SDKs, Terraform and Testcontainers can all talk to it using dummy credentials, with no AWS account in the loop. The project is hosted at github.com/floci-io/floci, and its name comes from cirrocumulus floccus, a cloud formation.

Two design decisions stand out, per dev.to. First, Floci is built on Quarkus and compiled to a GraalVM native binary, so there is no JVM or Python runtime to boot; the project advertises roughly 24 ms startup and about 13 MiB of idle memory, compared with LocalStack's advertised 3.3 seconds and 143 MiB. Second, it favours real containers over shallow stubs: invoking a Lambda pulls the genuine AWS runtime image and executes the function inside an actual container that is torn down afterwards, mirroring how AWS itself runs functions. Stateful services such as RDS (PostgreSQL and MySQL) and ElastiCache (Redis) also spin up as real containers on demand.

Capabilities that LocalStack keeps behind paid tiers — API Gateway v2, Cognito, S3 Object Lock and IAM-authenticated databases — are included at no cost. Floci's own site claims a 100% pass rate on a 1,925-test SDK compatibility suite, a figure dev.to notes is vendor-reported.

How the comparison shakes out

The candid summary from dev.to: Floci wins on footprint, friction and licensing, while LocalStack still wins on breadth of services and edge-case coverage thanks to its maturity. The article also cautions that independent hands-on checks show neither tool matches its advertised numbers — Floci measured closer to 130 ms in a cold real-world test rather than 24 ms, and LocalStack took several seconds rather than 3.3. What survives scrutiny, the author argues, is the order-of-magnitude gap, which matters most in CI pipelines where the emulator may start hundreds of times a day.

Setup and migration

Running Floci locally takes a short Docker Compose file referencing the hectorvent/floci image with port 4566 exposed. After starting the container, pointing the AWS CLI at localhost:4566 with dummy credentials lets you create S3 buckets and DynamoDB tables right away. A built-in web console lets you browse buckets and objects, inspect DynamoDB tables and records, view Lambda configurations and invoke functions with custom JSON payloads straight from the browser.

Migrating from LocalStack is described as a one-line image swap, since the port, endpoint and SDK configuration are identical. Floci also ships a Testcontainers module so the emulator's lifecycle runs inside a test suite rather than as a container managed separately. The article reports verifying a full serverless pipeline — an S3 upload triggering a Lambda that resizes an image into a second bucket and logs metadata to DynamoDB — running end-to-end just as it would on AWS, with the real Lambda runtime container doing the work.

Why it matters

The licensing change at LocalStack turned a routine piece of developer infrastructure into a subscription decision, and Floci is the most direct beneficiary. For solo developers and small teams it removes sign-ups, tokens stored in CI secrets and paywalled features; for CI-heavy teams the lighter footprint compounds across hundreds of runs per day. LocalStack's free Hobby plan remains a legitimate, low-effort option for those already invested, though dev.to notes its Community line gets no security fixes and pricing has already moved twice in 2026. The broader reassurance is portability: because both tools speak standard AWS APIs, tests written against either remain transferable if circumstances change again.