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Cache where you keep your grain.

📖 Documentation: https://chrisjenx.github.io/silo/

What is Silo?

Silo is a self-hosted HTTP server that speaks the Gradle build cache protocol. It is a drop-in replacement for the now-EOL Gradle Remote Build Cache Node. Written in Kotlin on Ktor. Ships as a fat jar or a multi-arch Docker image. Apache-2.0. Free forever.

Why

Gradle Inc. has deprecated the free standalone Build Cache Node in favor of the paid Develocity product. Teams who want a self-hostable, no-account-required, no-license-fee build cache had no maintained option. Silo fills that gap.

• One binary. One volume. One port.
• No phone-home. No telemetry. No accounts.
• Atomic writes — kill -9 mid-PUT cannot corrupt the cache.
• LRU + TTL + size + entry-count caps, all enforced together.
• Self-healing against out-of-band deletes.
• Prometheus metrics + retro-terminal admin dashboard.

Features

• Full Gradle HTTP build cache protocol (GET, PUT, HEAD)
• Pluggable storage — filesystem in v0.1; S3 and GCS planned for v0.2
• HTTP Basic auth with read-only and read-write user split
• LRU eviction with TTL, byte-cap, entry-cap, and reserved-free-space thresholds
• Prometheus /metrics, JSON-structured logs, /health and /ready
• Retro-terminal admin SPA (Kobweb) — phosphor green, amber CRT, or paper-tape themes
• Atomic content-addressed writes with SQLite (WAL) metadata index
• Multi-arch Docker (linux/amd64, linux/arm64) and a single fat jar
• JVM 21+ — virtual threads, modern Ktor, no native image required

Quick start

Docker

docker run -d --name silo \
  -p 8080:8080 \
  -v silo-data:/data \
  ghcr.io/chrisjenx/silo:latest

Fat jar

curl -L https://github.com/chrisjenx/silo/releases/latest/download/silo.jar -o silo.jar
java -jar silo.jar

docker-compose

See examples/docker-compose.yml. Includes a named volume, env-var auth, and a sidecar Caddy reverse proxy for HTTPS.

Configure Gradle to use Silo

In your project's settings.gradle.kts:

buildCache {
    remote<HttpBuildCache> {
        url = uri("http://localhost:8080/cache/")  // trailing slash is required
        push = true
        credentials {
            username = "ci-writer"
            password = System.getenv("SILO_CACHE_PASSWORD")
        }
    }
}

See examples/gradle-settings-snippet.kts for the full snippet.

Admin UI

Silo ships a single-page admin dashboard at /admin. The design language is intentionally terminal — phosphor green on black, ASCII box-drawing, Unicode block sparklines, no chart libraries. See docs/design.md for the full spec.

▶ Try the live demo — the real admin UI running on simulated data, right in your browser. No install, no backend.

Configuration

Silo is configured via HOCON (application.conf) with environment-variable overrides.

Env var	HOCON key	Default	Purpose
SILO_PORT	silo.server.port	8080	HTTP listen port
SILO_STORAGE_ROOT	silo.storage.root	/data	Data directory
SILO_MAX_BYTES	silo.storage.max-bytes	107374182400 (100 GiB)	Total cache size cap
SILO_MAX_ENTRIES	silo.storage.max-entries	1000000	Total entry cap
SILO_MAX_ENTRY_BYTES	silo.storage.max-entry-bytes	2147483648 (2 GiB)	Per-entry cap
SILO_MAX_AGE_DAYS	silo.eviction.max-age-days	30	TTL for untouched entries
SILO_USERS_FILE	silo.auth.users-file	(unset)	bcrypt user list
SILO_ANONYMOUS_READ	silo.auth.anonymous-read	true	Allow unauthenticated GET/HEAD

Full reference: docs/configuration.md. Hardware, requirements, and limits: docs/limits.md.

Documentation

The full docs site is published at https://chrisjenx.github.io/silo/.

• Live dashboard demo — the admin UI on simulated data, no install
• Configuration reference — every HOCON key and env override
• Requirements & limits — hardware sizing, caps, FS, ulimit, NFS
• Reverse proxy & TLS — termination at a proxy, inline TLS opt-in
• Operations runbook — backup, restore, recovery
• Design language — the retro-terminal admin UI spec

Comparison

Feature	Silo v0.1	Develocity Build Cache Node
License	Apache-2.0	Commercial
Cost	Free	Per-seat
Self-host	Yes	Yes
Phone-home telemetry	No	Yes
Storage backends	Filesystem	Filesystem, S3
Admin UI	Retro terminal	Standard
Atomic writes	Yes	Yes
TTL eviction	Yes	Yes
Multi-arch Docker	linux/amd64, linux/arm64	linux/amd64
Replication	Planned (v0.3+)	Yes
Resource footprint	~150 MB RAM idle	~1 GB+

Not affiliated with or endorsed by Gradle Inc. or Gradle Build Tool®.

Status

Alpha. The v0.1 walking-skeleton is complete and released (latest v0.1.x); work continues on v0.2 hardening (S3/GCS backends, compression, replication).

Building from source

./gradlew :server:shadowJar
java -jar modules/server/build/libs/silo-*-all.jar

Contributing

See CONTRIBUTING.md. Good first issues are labelled good-first-issue.

Security

See SECURITY.md for the vulnerability disclosure policy.

License

Apache-2.0 — see LICENSE.