CallFS – S3-style object store in one Go binary (MIT)
We started CallFS after yet another late-night “why did the uploads vanish?” incident. Our small team had stitched together rsync, a fragile NFS mount, and an S3 bucket—none of it observable, all of it waiting to bite us. So we wrote a single-process file service in Go that: • Speaks the S3 API (so existing tooling works). • Stores hot data on local disks for speed; cold data can sit in any S3-compatible bucket. • Exposes Prometheus metrics and JSON logs by default, because “what happened?” shouldn’t be guesswork. • Ships as a ~25 MB static binary—no external deps, MIT license. Today it’s…
In plain words
CallFS is an S3-compatible object storage service built as a single Go binary. It stores frequently accessed data locally on disk for speed while archiving cold data to S3-compatible buckets. The service includes built-in Prometheus metrics and JSON logging for full observability, addressing the reliability challenges of fragmented storage systems. It requires no external dependencies, ships as a 25 MB binary, and is suitable for teams running single-node or parallel deployments.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
We started CallFS after yet another late-night “why did the uploads vanish?” incident. Our small team had stitched together rsync, a fragile NFS mount, and an S3 bucket—none of it observable, all of it waiting to bite us. So we wrote a single-process file service in Go that: • Speaks the S3 API (so existing tooling works). • Stores hot data on local disks for speed; cold data can sit in any S3-compatible bucket. • Exposes Prometheus metrics and JSON logs by default, because “what happened?” shouldn’t be guesswork. • Ships as a ~25 MB static binary—no external deps, MIT license. Today it’s stable for single-node or side-by-side deployments. Clustering is on the roadmap, replication will follow, but we wanted to share the code early and hear real-world pain points. If storage glue code ever ruined your weekend, we’d love feedback and PRs.
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