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EmgR

Welcome to the documentation for EmgR, a high-performance, imgproxy-compatible image resizing service built in Rust. It fetches a source image over HTTP(S), resizes/transforms it according to a signed URL, caches the result, and redirects the caller to it.

Features

  • On-the-fly resizing via an imgproxy-compatible signed URL scheme - resize/crop, gravity, quality, blur, grayscale, watermarks and named presets.
  • JPEG, PNG, WebP (lossy and lossless), AVIF and animated GIF/WebP output, through a SIMD resampler (fast_image_resize) and a mozjpeg-backed JPEG decode/encode path (DCT-scaled decode, progressive/subsampling control).
  • Pluggable storage backends selected at compile time via Cargo feature flags: local filesystem, S3/MinIO, or in-memory (test builds only).
  • HMAC-signed URLs on by default, an SSRF-guarded source fetcher, and configurable resolution/output limits.
  • OpenTelemetry tracing and a bearer-token-protected /metrics endpoint, available behind the otel feature.
  • Kubernetes deployment via a Helm chart (or a Knative Service chart for serverless setups).

Before you start

Two things surprise newcomers, and both are deliberate:

  1. emgr has no default storage backend. Cargo.toml sets default = [], so a plain cargo build compiles but the resulting binary refuses to start ("No storage features are enabled"). Every build must name at least one of local_fs, s3, or in_memory explicitly.
  2. The service fails closed at startup unless signed URLs are configured (SIGNING_KEY + SIGNING_SALT) or you explicitly opt out with ALLOW_UNSIGNED_REQUESTS=true. A build with the otel feature adds a second, independent check for /metrics.

See Getting Started → Installation for the full explanation, the exact commands, and every feature combination CI tests.

Quick start

git clone https://github.com/vaam-store/image-resizer.git
cd image-resizer

# local_fs storage, signing turned off for local dev only - see
# Installation for the signed-URL alternative. --bin is required because
# the crate also ships `healthcheck` and `benchmark` binaries.
LOCAL_FS_STORAGE_PATH=./data/images ALLOW_UNSIGNED_REQUESTS=true \
  cargo run --no-default-features --features local_fs --bin emgr

curl -i http://localhost:3000/health

API overview

The service exposes a RESTful, imgproxy-compatible resize endpoint plus a download endpoint for already-cached results. See the API Reference for the full URL grammar, status codes and processing options, and Examples for computing a valid signature in Python/JavaScript/bash.

Architecture

The service is a hand-written Axum router (no OpenAPI code generation) over a small set of modular Rust services. See the architecture overview and components pages.

Deployment

Run it with Docker, or deploy it to Kubernetes with the Helm chart.