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hyperhive/swarm-builder
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Repository files (latest commit first)
Filename Latest commit message Latest commit date
atlas e873195cf6 swarm-builder: keep only the tail of nix's output while it runs 
nix_build::run read nix's stdout and stderr with read_to_end, so a long
--print-build-logs run held its whole log in memory until nix exited,
though the reply uses only the last 30 lines (4000 bytes) of stderr and
the last non-empty line of stdout. Both streams now go through a Tail
that holds at most 128 KiB and keeps the last 64 KiB. Output under 64 KiB
reaches tail() whole, so those replies are unchanged.
2026-10-17 08:45:42 +02:00
..
src swarm-builder: keep only the tail of nix's output while it runs 2026-10-17 08:45:42 +02:00
Cargo.toml swarm-builder: build each agent config PR head and post a commit status 2026-10-14 03:30:46 +02:00
README.md docs: builder.md says the client secret is re-read on refusal too 2026-10-14 03:30:46 +02:00

README.md

swarm-builder

The swarm builder's build service, in the swarm-builder container on the host that sets deploy.builder.enable. The design is docs/swarm/builder.md.

swarm-controller sends one request per config PR head: an agent, a commit and the PR. This service builds that agent config on the agent base this host was deployed with, through the host's nix daemon, and answers with the system closure's store path or the tail of what nix printed. The controller turns the answer into a swarm-builder commit status on the PR's head.

What a build is

  • nix build of nix/builder/check-flake's check output, with its three inputs overridden: hyperhive and nixpkgs to this host's own sources, and agent to git+https://<forge>/agent-configs/<agent>?ref=refs/pull/<pr>/head&rev=<rev>.
  • The evaluation runs here, pure; the builds run in the host daemon's sandbox as an untrusted client, so a config can neither set daemon options nor read this service's environment.
  • Nothing is pushed and nothing is recorded: the closure stays in the host's store until it is collected.

Credentials

The container holds one credential: its own store certificate, which nspawn hands in at start without a copy on disk. With it the service reads its queue client secret at start and again when authelia refuses it, and its read-only forge token at every build. git gets the token through a credential helper reading the child's environment, never in a URL or an argument, and the helper answers only an https request for the forge's host. Its store role reads exactly those two paths.