Meet Floci: a fast, free, no-strings AWS emulator (no auth token, no quotas)

If you write code against AWS, you've probably hit one of these in the last year:

• LocalStack Community Edition sunset in March 2026. Auth tokens, frozen security updates, paid tiers for the things that used to be free.
• Spinning up real AWS for local dev or CI is slow, expensive, and risky.
• Mock libraries lie to you until production day.

I started Floci to fix this. It's a single Docker image, MIT-licensed, no account, no telemetry, no feature gates. Pull and go.

TL;DR: docker run -p 4566:4566 floci/floci:latest and you have 40+ AWS services on http://localhost:4566. Same port and SDK calls as LocalStack. Switch by changing one env var.

🔗 GitHub: github.com/floci-io/floci
🔗 Docs: floci.io/floci

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Why I built it

I was tired of three things:

1. Hidden costs. Free emulators that "encourage" you toward a paid tier the moment your team grows past 1.
2. Slow startup. Booting an emulator that takes 3+ seconds for every CI job multiplies into hours of waste per week.
3. Mock-only fidelity. Some services (Lambda, RDS, ElastiCache, Athena, EKS) need a real engine, not a JSON shim that pretends.

Floci is what I wished existed.

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What makes Floci different

1. It's actually fast

Floci is built on Quarkus + GraalVM native image. No JVM warmup, no Python interpreter startup.

	Floci	LocalStack
Cold start	~24 ms	~3,300 ms
Idle memory	~13 MiB	~143 MiB
Image size	~90 MB	~2 GB

That gap is why Floci is comfortable on your smallest CI runner. A test that spins up a fresh emulator per job suddenly stops being painful.

2. Real Docker where it matters

Mock-only emulators are fine until your code starts depending on the real engine's behavior. Floci spins up real Docker containers for the services where wire protocols and execution semantics matter:

• Lambda: real container per function, warm pool, aliases, Function URLs, SQS/Kinesis/DDB Streams event source mappings
• RDS: actual PostgreSQL and MySQL containers with JDBC wire protocol proxying
• ElastiCache: real Redis/Valkey with RESP proxying and IAM/SigV4 token validation
• MSK: real Apache Kafka clusters
• OpenSearch / EKS / ECS: real engines and orchestrators where applicable

This is the architecture from day one, not a feature flag, not a paid add-on.

3. Genuinely free and open

• MIT licensed. Fork it, embed it, ship it inside your product. No "community edition sunset" coming.
• No auth token. Ever.
• No telemetry. Floci doesn't phone home.
• No CI quota. Run 100,000 jobs a day if you want.
• No feature gates. Every supported service is available to everyone.

4. Wire-compatible with the real AWS SDKs

Floci is validated by 1,850+ automated compatibility tests running across:

• AWS SDK for Java v2
• AWS SDK for JavaScript v3
• boto3 (Python)
• AWS CLI v2
• AWS SDK for Go v2
• AWS SDK for Rust
• Terraform / OpenTofu / AWS CDK

The principle: the SDK source is the contract. If the official SDK can't tell Floci apart from AWS at the wire level, the test passes. If it can, that's a bug.

5. Drop-in for LocalStack users

Same default port (4566). Same wire protocols. Same SDK endpoint override. Migration is one env var:

- AWS_ENDPOINT_URL=http://localstack:4566
+ AWS_ENDPOINT_URL=http://floci:4566

That's it. Your application code, your IaC, your tests, all unchanged.

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The 30-second tour

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

docker compose up -d

# Overwrite the aws-cli default URL endpoint
export AWS_ENDPOINT_URL="http://localhost:4566"

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

In Java with the AWS SDK v2:

S3Client s3 = S3Client.builder()
    .endpointOverride(URI.create("http://localhost:4566"))
    .region(Region.US_EAST_1)
    .credentialsProvider(StaticCredentialsProvider.create(
        AwsBasicCredentials.create("test", "test")))
    .forcePathStyle(true)
    .build();

Done.

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Testcontainers integration (it just works)
If you write JUnit/Spring Boot tests, there's an official Testcontainers module on Maven Central. No manual GenericContainer setup, no port juggling.

<dependency>
    <groupId>io.floci</groupId>
    <artifactId>testcontainers-floci</artifactId>
    <version>2.1.0</version>
    <scope>test</scope>
</dependency>

Then in your test:

@Testcontainers
class S3IntegrationTest {

    @Container
    static FlociContainer floci = new FlociContainer();

    @Test
    void shouldCreateBucket() {
        S3Client s3 = S3Client.builder()
            .endpointOverride(URI.create(floci.getEndpoint()))
            .region(Region.of(floci.getRegion()))
            .credentialsProvider(StaticCredentialsProvider.create(
                AwsBasicCredentials.create(floci.getAccessKey(), floci.getSecretKey())))
            .forcePathStyle(true)
            .build();

        s3.createBucket(b -> b.bucket("my-bucket"));
    }
}

There's also spring-boot-testcontainers-floci for Spring Boot users. auto-configures Spring Cloud AWS to point at the container, zero boilerplate.
Module page: testcontainers.com/modules/floci

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What's supported today

40+ services and growing. The big ones: S3, SQS, SNS, DynamoDB (+ Streams), Lambda, API Gateway v1 & v2, Cognito, KMS, Secrets Manager, IAM, STS, Step Functions, CloudFormation, EventBridge (+ Scheduler), CloudWatch Logs/Metrics, Kinesis, ElastiCache (Redis/Valkey), RDS (PostgreSQL/MySQL), ECS, EC2, OpenSearch, EKS, MSK, Glue, Athena, Data Firehose, ACM, AppConfig, Bedrock Runtime, SES/SES v2, SSM Parameter Store, etc.

Full per-service operation list: floci.io/floci/services

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Where it's heading

• EC2 with real Docker-backed compute (alpha)
• Quarkus DevServices integration for Java devs
• A per-language, per-service compatibility status dashboard

If any of that interests you or if a service you need isn't there yet, I'd love your input. Floci already has a great roster of contributors fixing real bugs and adding real services. There's room for more.

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How to help

If Floci sounds useful:

⭐ Star the repo: github.com/floci-io/floci. It genuinely helps surface the project to other devs in the same boat
💬 Join Slack: community workspace at floci.slack.com. Questions, feedback, and weird edge cases all welcome
🐛 Open an issue: found a wire-level mismatch with the real AWS SDK? That's exactly the kind of bug I want to know about
🤝 Contribute: good first issues are labeled, and PRs that add a missing API operation are very welcome

Thanks for reading and if you give Floci a try, let me know what works and what doesn't. The whole point is to be the emulator developers actually want to use.

Comments

[Cristian de la Hoz]

I will give it a try!