post3

S3-compatible object storage you can run anywhere.

post3 is a lightweight, self-hosted S3-compatible storage server written in Rust. Store objects in PostgreSQL or on the local filesystem — your choice, same API. Works with any S3 client: the AWS SDK, the AWS CLI, boto3, MinIO client, or plain curl.

Why post3?

• Drop-in S3 compatibility — 20+ S3 operations, validated against the Ceph s3-tests conformance suite (124 tests passing)
• Two backends, one API — PostgreSQL (objects chunked into 1 MiB blocks) or local filesystem. Swap at startup with a flag.
• Zero external dependencies for FS mode — No database, no message queue, no cloud account. Just the binary and a directory.
• Multipart uploads — Full support for creating, uploading parts, completing, aborting, and listing multipart uploads. 5 GiB body limit.
• Custom metadata — x-amz-meta-* headers preserved and returned on GET/HEAD
• Rust SDK included — Ergonomic client wrapping aws-sdk-s3 with sane defaults. One-liner setup.
• Built on proven foundations — axum, tokio, sqlx, tower. Production-grade async Rust.

Quick Start

Filesystem backend (no database needed)

# Build and run
cargo build --release -p post3-server
./target/release/post3-server serve --backend fs --data-dir /tmp/post3-data

PostgreSQL backend

# Start PostgreSQL and the server
mise run up    # docker compose up (PostgreSQL 18)
mise run dev   # start post3-server on localhost:9000

Try it out

# Create a bucket
curl -X PUT http://localhost:9000/my-bucket

# Upload an object
curl -X PUT http://localhost:9000/my-bucket/hello.txt \
  -d "Hello, post3!"

# Download it
curl http://localhost:9000/my-bucket/hello.txt

# List objects
curl http://localhost:9000/my-bucket?list-type=2

# Delete
curl -X DELETE http://localhost:9000/my-bucket/hello.txt
curl -X DELETE http://localhost:9000/my-bucket

Or use the AWS CLI:

alias s3api='aws s3api --endpoint-url http://localhost:9000 --no-sign-request'

s3api create-bucket --bucket demo
s3api put-object --bucket demo --key readme.md --body README.md
s3api list-objects-v2 --bucket demo
s3api get-object --bucket demo --key readme.md /tmp/downloaded.md

Rust SDK

[dependencies]
post3-sdk = { path = "crates/post3-sdk" }

use post3_sdk::Post3Client;

let client = Post3Client::new("http://localhost:9000");

client.create_bucket("my-bucket").await?;
client.put_object("my-bucket", "hello.txt", b"Hello, world!").await?;

let data = client.get_object("my-bucket", "hello.txt").await?;
assert_eq!(data.as_ref(), b"Hello, world!");

// Large files — automatic multipart upload
client.multipart_upload("my-bucket", "big-file.bin", &large_data, 8 * 1024 * 1024).await?;

// List with prefix filtering
let objects = client.list_objects("my-bucket", Some("logs/")).await?;

Since post3-sdk re-exports aws_sdk_s3, you can drop down to the raw AWS SDK for anything the convenience API doesn't cover.

Supported S3 Operations

Category	Operations
Buckets	CreateBucket, HeadBucket, DeleteBucket, ListBuckets, GetBucketLocation
Objects	PutObject, GetObject, HeadObject, DeleteObject
Listing	ListObjects (v1 & v2), ListObjectVersions, delimiter/CommonPrefixes
Batch	DeleteObjects (up to 1000 keys)
Multipart	CreateMultipartUpload, UploadPart, CompleteMultipartUpload, AbortMultipartUpload, ListParts, ListMultipartUploads
Metadata	Custom x-amz-meta-* headers on PUT, returned on GET/HEAD

Architecture

crates/
  post3/           Core library — StorageBackend trait, PostgresBackend,
                   FilesystemBackend, models, migrations
  post3-server/    HTTP server — axum-based, generic over any StorageBackend
  post3-sdk/       Client SDK — wraps aws-sdk-s3 with ergonomic defaults
ci/                CI pipeline — custom Dagger-based build/test/package

The server is generic over B: StorageBackend. Both backends implement the same trait, so the HTTP layer doesn't know or care where bytes end up.

PostgreSQL backend splits objects into 1 MiB blocks stored as bytea columns. Seven tables with ON DELETE CASCADE for automatic cleanup. Migrations managed by sqlx.

Filesystem backend uses percent-encoded keys, JSON metadata sidecars, and atomic writes (write-to-temp + rename). No database required.

S3 Compliance

post3 is validated against the Ceph s3-tests suite — the same conformance tests used by Ceph RGW, s3proxy, and other S3-compatible implementations.

124 passed, 0 failed, 0 errors

Run them yourself:

git submodule update --init
mise run test:s3-compliance       # run tests
mise run test:s3-compliance:dry   # list which tests would run

Development

Requires mise for task running.

mise run up                # Start PostgreSQL via docker compose
mise run dev               # Run the server (localhost:9000)
mise run test              # Run all tests
mise run test:integration  # S3 integration tests only
mise run check             # cargo check --workspace
mise run build             # Release build
mise run db:shell          # psql into dev database
mise run db:reset          # Wipe and restart PostgreSQL

Examples

mise run example:basic      # Bucket + object CRUD
mise run example:metadata   # Custom metadata round-trip
mise run example:aws-sdk    # Raw aws-sdk-s3 usage
mise run example:cli        # AWS CLI examples
mise run example:curl       # curl examples
mise run example:large      # Large file stress test
mise run example:multipart  # Multipart upload stress test

Configuration

Variable	Default	Description
POST3_HOST	127.0.0.1:9000	Address to bind
DATABASE_URL	—	PostgreSQL connection string (pg backend)
--backend	pg	Storage backend: pg or fs
--data-dir	—	Data directory (fs backend)

License

Licensed under the MIT License.