Hydra vs Semaphore

Hydra is a continuous integration service for projects based on Nix. It checks out project source periodically or continuously, builds it, runs tests, and produces reports. Work is organized into jobsets whose inputs can trigger builds when they change; jobsets can also depend on one another. Flake jobsets are supported when their outputs expose a hydraJobs attribute set. Jobs can produce packages, ISO images, or tarballs, and jobset inputs can use Git checkout sources. Hydra also provides a JSON API. It is aimed at Nix and NixOS package developers, not people who only need to use NixOS. Hydra is open source under GPL-3.0 and listed at free. It is self-hosted, with no hosted option listed, and running it is currently supported only on NixOS; the repository recommends the NixOS module for production. Flake evaluation is restricted from accessing files outside the Nix store. Some state is stored in the database, so backups are needed, and the wiki reports that hydra-queue-runner can sometimes leave queued builds unscheduled.

Semaphore is an AI-native CI/CD platform for building, testing, releasing, and deploying code. Teams organize automated development tasks into workflows containing one or more pipelines. Its visual Workflow Builder represents pipelines, creates YAML configuration, and displays performance feedback. Repositories can connect from GitHub, GitLab, or Bitbucket. Teams can use hosted jobs or run self-hosted agents on Linux, macOS, or Windows; those agents can autoscale with Kubernetes or AWS. Semaphore is open source under Apache 2.0 and can be self-hosted. The default concurrency is 20 jobs, with higher limits available on request. Artifact use is free up to 20 GB monthly egress and 100 GB monthly storage; additional usage is charged separately. A free plan includes account, project, and Git integration assistance, while advanced CI troubleshooting is offered through paid support. Listed paid support begins with Basic Support at $50 a month. Semaphore says data is encrypted in transit and at rest, and that it holds SOC 2 Type 2 and ISO 27001:2022 certifications. Pricing includes free usage credits and per-minute compute charges.