EngFlow Remote Caching vs Harmonia

EngFlow Remote Caching is a remote cache service for reducing repeated builds and test reruns, developer workload, and compute costs. It uses gRPC, cache compression, and Build without the Bytes to limit latency and unnecessary data transfers. A layered cache keeps frequently requested data available, while the Build & Test UI reports cache hit rates, build time, and status in real time. The Free tier supports Bazel and provides in-cluster caching on one machine with 32 CPU cores, running Linux. Enterprise supports Bazel, Goma for Chromium, and Soong for AOSP, as well as in-cluster or external storage such as S3 and GCS. Free is self-hosted; Enterprise can be self-hosted or managed. The service is available for Linux, macOS, Windows, web, and API use. EngFlow says builds run in isolated, encrypted environments with dedicated infrastructure by default, and its solutions receive regular third-party audits against the five SOC 2 principles. Free costs nothing; Enterprise pricing is custom quote. A trial request form is available, with no duration stated.

Harmonia is free, open-source software for serving a Nix store as a binary cache over HTTP. Written in Rust for Linux self-hosting, it supports HTTP range requests for NAR streaming and streaming build logs. The /serve// endpoint can provide package contents and discover index.html to serve websites directly from the Nix store. Harmonia can transparently compress content with zstd and provide TLS when no frontend web server is used. Documentation covers a NixOS module and nginx HTTPS frontend configuration for a public cache. Narinfo signing is disabled unless private signing-key paths are supplied. Prometheus metrics are available at /metrics, with a Grafana dashboard included in the repository. Since version 3.1.0, metadata is read directly from db.sqlite without a nix-daemon connection. Version 3.3.0 adds harmonia-gc for removing store garbage while nix-daemon builds. It uses the MIT License.