Floci: The Free, Open-Source AWS Emulator That Replaced LocalStack

In March 2026, something quietly shifted in the AWS local development world. LocalStack's Community Edition reached end-of-life — no more security updates, and a mandatory auth token requirement that broke countless CI pipelines, Docker Compose setups, and dev environments overnight. For years, LocalStack had been the go-to tool for running AWS locally. Now it was asking for credentials just to spin up an S3 bucket on your laptop.

That's where Floci enters the story.

What Is Floci?

Floci is a free, open-source, MIT-licensed AWS local emulator built with Quarkus Native. Named after cirrocumulus floccus — the cloud formation that looks exactly like popcorn 🍿 — it's designed to be a true drop-in replacement for LocalStack: same port (4566), same credentials format, same AWS wire protocol. You swap the Docker image, and your existing code just works.

No account. No API key. No feature gates. No telemetry. No surprises. Just docker compose up.

The Numbers That Actually Matter

Benchmarks can be cherry-picked, but the Floci vs LocalStack comparison is striking enough to call out directly:

24 milliseconds to start. Not seconds — milliseconds. This is the power of Quarkus Native compilation: the JVM overhead is eliminated entirely, and the binary boots as fast as a regular command-line tool. For CI/CD pipelines that spin up infrastructure containers for every test run, this difference compounds significantly.

Real Services, Not Mocks

One of the common complaints about local AWS emulators is that they mock services too superficially — you write code against the emulator, ship to production, and then discover the real AWS behavior is subtly different. Floci takes a different approach for its most critical services.

Lambda, ElastiCache, RDS, and ECS spin up actual Docker containers. When you deploy a Lambda function to Floci, a real container runs it. When you create an ElastiCache cluster, a real Redis/Valkey container starts. When you provision an RDS instance, a real PostgreSQL or MySQL container comes up — JDBC-compatible, ready for real SQL.

This matters. It means wire protocol fidelity. SigV4 signing. IAM auth that actually validates. The same code you run locally against Floci will behave identically against AWS.

Service Coverage

Floci supports 41 AWS services across the board. Here are some highlights that LocalStack Community Edition either didn't support or only partially implemented:

• API Gateway v2 (HTTP API) — Routes, integrations, JWT authorizers, stages
• Cognito — User pools, app clients, full auth flows, JWKS/OpenID endpoints
• ElastiCache — Redis + Valkey with real Docker containers and IAM auth
• RDS — PostgreSQL & MySQL with real containers, IAM auth, JDBC-compatible
• ECS — 58 operations: clusters, task definitions, services, capacity providers
• DynamoDB Streams — Full shard iterators, records, Lambda ESM trigger
• KMS — Sign, verify, re-encrypt — not just encrypt/decrypt stubs
• IAM — 65+ operations: users, roles, groups, policies, instance profiles

The compatibility test suite tells the full story: 1,873 automated tests run against Java, Node.js, Python, Go, Rust, AWS CLI, Terraform, OpenTofu, and CDK. That's not confidence by assertion — it's confidence by evidence.

Getting Started in 30 Seconds

If you've used LocalStack before, migrating is literally a one-line change:

# docker-compose.yml
services:
  floci:
    image: floci/floci:latest
    ports:
      - "4566:4566"
    volumes:
      - ./data:/app/data

docker compose up

export AWS_ENDPOINT_URL=http://localhost:4566
export AWS_DEFAULT_REGION=us-east-1
export AWS_ACCESS_KEY_ID=test
export AWS_SECRET_ACCESS_KEY=test

aws s3 mb s3://my-bucket
aws sqs create-queue --queue-name my-queue
aws dynamodb list-tables

Point your SDK at http://localhost:4566, use test/test as credentials, and you're done. Python (boto3), Java (AWS SDK v2), Node.js (AWS SDK v3), Go, Rust — all work unchanged.

Architecture: Why It's So Fast

The architecture is elegantly simple. A single HTTP router (built on JAX-RS + Vert.x) handles all 41 services on port 4566. Services are split into three categories:

• Stateless services (SSM, SQS, SNS, IAM, STS, KMS, Cognito, etc.) — run entirely in-process
• Stateful services (S3, DynamoDB) — run in-process with configurable storage backends: memory, persistent, hybrid, or wal
• Container services (Lambda, ElastiCache, RDS, ECS) — spawn real Docker containers via the Docker API

Building on Quarkus Native means the binary is ~40 MB and starts in under 25ms. The entire "server" is a single native binary — no JVM warm-up, no ClassLoader overhead, no Python interpreter startup.

The Bigger Picture

The LocalStack sunset wasn't just inconvenient — it revealed a structural problem: depending on a company-controlled tool for a core part of your local development workflow means accepting their business decisions. When auth tokens appeared overnight, teams scrambled. CI pipelines broke. Staging environments went down.

Floci's commitment is simple: MIT-licensed, forever free, no auth tokens, no feature gates. The GitHub repo has already crossed 2,700 stars in a very short time. The community Slack is active. Issues are being triaged and closed quickly.

This is what a healthy open-source response to proprietary lock-in looks like.

Should You Switch?

If you were using LocalStack Community Edition, yes — switch today. The migration is trivial (update the image name), you gain a faster startup, dramatically smaller footprint, and more features. You lose nothing except the dependency on an auth token you never wanted in the first place.

If you're starting a new project that needs local AWS services, Floci is now the obvious first choice.

The repo is at github.com/floci-io/floci. Give it a star — open source projects like this deserve the visibility.