S2, the durable streams API

s2.dev is a serverless datastore for real-time, streaming data.

This repository contains:

• s2-cli - The official S2 command-line interface
• s2-lite - An open source, self-hostable server implementation of the S2 API

Installation

Homebrew (macOS/Linux)

brew install s2-streamstore/s2/s2

Cargo

cargo install --locked s2-cli

Release Binaries (macOS/Linux)

curl -fsSL https://raw.githubusercontent.com/s2-streamstore/s2/main/install.sh | bash

Or specify a version with VERSION=x.y.z before the command. See all releases.

Docker

docker pull ghcr.io/s2-streamstore/s2

s2-lite

s2-lite is embedded as the s2 lite subcommand of the CLI. It's a self-hostable server implementation of the S2 API.

It uses SlateDB as its storage engine, which relies entirely on object storage for durability.

It is easy to run s2 lite against object stores like AWS S3 and Tigris. It is a single-node binary with no other external dependencies. Just like s2.dev, data is always durable on object storage before being acknowledged or returned to readers.

You can also simply not specify a --bucket, which makes it operate entirely in-memory (or use --local-root to persist to local disk instead).

Tip

In-memory s2-lite is a very effective S2 emulator for integration tests.

Quickstart

Here's how you can run in-memory without any external dependency:

# Using Docker
docker run -p 8080:80 ghcr.io/s2-streamstore/s2 lite

# Or directly with the CLI
s2 lite --port 8080

AWS S3 bucket example

docker run -p 8080:80 \
  -e AWS_PROFILE=${AWS_PROFILE} \
  -v ~/.aws:/home/nonroot/.aws:ro \
  ghcr.io/s2-streamstore/s2 lite \
  --bucket ${S3_BUCKET} \
  --path s2lite

Static credentials example (Tigris, R2 etc)

docker run -p 8080:80 \
  -e AWS_ACCESS_KEY_ID=${AWS_ACCESS_KEY_ID} \
  -e AWS_SECRET_ACCESS_KEY=${AWS_SECRET_ACCESS_KEY} \
  -e AWS_ENDPOINT_URL_S3=${AWS_ENDPOINT_URL_S3} \
  ghcr.io/s2-streamstore/s2 lite \
  --bucket ${S3_BUCKET} \
  --path s2lite

Note

Point the S2 CLI or SDKs at your lite instance like this:

export S2_ACCOUNT_ENDPOINT="http://localhost:8080"
export S2_BASIN_ENDPOINT="http://localhost:8080"
export S2_ACCESS_TOKEN="ignored"

Let's make sure the server is ready:

while ! curl -sf ${S2_ACCOUNT_ENDPOINT}/health -o /dev/null; do echo Waiting...; sleep 2; done && echo Up!

Install the CLI (see Installation above) or upgrade if s2 --version is older than 0.26

Let's create a basin with auto-creation of streams enabled:

s2 create-basin liteness --create-stream-on-append --create-stream-on-read

Test your performance:

s2 bench liteness --target-mibps 10 --duration 5s --catchup-delay 0s

Now let's try streaming sessions. In one or more new terminals (make sure you re-export the env vars noted above),

s2 read s2://liteness/starwars 2> /dev/null

Now back from your original terminal, let's write to the stream:

nc starwars.s2.dev 23 | s2 append s2://liteness/starwars

Monitoring

/health will return 200 on success for readiness and liveness checks

/metrics returns Prometheus text format

Internals

SlateDB settings

Settings reference

Use SL8_ prefixed environment variables, e.g.:

# Defaults to 50ms for remote bucket / 5ms in-memory
SL8_FLUSH_INTERVAL=10ms

Design

Concepts

• HTTP serving is implemented using axum
• Each stream corresponds to a Tokio task called streamer that owns the current tail position, serializes appends, and broadcasts acknowledged records to followers
• Appends are pipelined to improve performance against high-latency object storage
• lite::backend::kv::Key documents the data modeling in SlateDB

Tip

Pipelining is temporarily disabled by default, and it will be enabled once it is completely safe. For now, you can use S2LITE_PIPELINE=true to get a sense of what performance will look like.

Compatibility

• CLI ✅ v0.26+
• TypeScript SDK ✅ v0.22+
• Go SDK ✅ v0.11+
• Rust SDK ✅ v0.22+
• Python 🚧 needs to be migrated to v1 API
• Java 🚧 needs to be migrated to v1 API

API Coverage

Complete specs are available:

• OpenAPI for the REST-ful core
• Protobuf definitions
• S2S, which is the streaming session protocol

Important

Unlike the cloud service where the basin is implicit as a subdomain, /streams/* requests must specify the basin using the S2-Basin header. The SDKs take care of this automatically.

Endpoint	Support
/basins	Supported
/streams	Supported
/streams/{stream}/records	Supported
/access-tokens	Not supported #28
/metrics	Not supported