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59 lines
2.6 KiB
Markdown
59 lines
2.6 KiB
Markdown
# swarm-controller
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The **swarm-level** daemon. Where `hive-c0re` owns the agents on one host, this
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owns what is true _across_ hives — so a swarm runs one of them and most hives
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leave it off.
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Opt-in per host via `services.hyperhive.deploy.swarm-controller.enable`, which is
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deliberately **not** derived from `services.hyperhive.enable`: turning it on is
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a statement about swarm topology, not about whether hyperhive is installed.
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## What it does today
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Serves one `/health` endpoint and holds no state.
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That is the whole intent of the first slice. The point is to make the _unit_
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real — service user, runtime and state directories, socket, nginx
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reachability — so the swarm-level surfaces that follow have somewhere to land.
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Inventing those surfaces before they are agreed would bake in a shape nobody
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chose. See #3066 and the `hyperhive.swarm` consolidation epic.
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## Why a unix socket, not a port
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The hive-gateway's nginx is the only intended client and reaches the socket
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through a bind-mount. A listener that is never bound to an address cannot be
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reached from off-host by mistake.
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The socket path is `services.hyperhive.swarm.controller.socketPath`, default
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`/run/swarm-controller/controller.sock`, exported to the process as
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`SWARM_CONTROLLER_SOCKET`.
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## ⚠️ The socket's directory is its access control
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The socket is `0666`. It has to be: nginx runs as a different user and
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`connect(2)` needs write. This matches how `hive-c0re` publishes the per-agent
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sockets, and rests on the same argument — _"the bind source dir is per-agent on
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host so blast radius is unchanged."_
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What keeps that safe is that the directory holds **one** socket. So:
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> **Never point `socketPath` at a directory that carries anything else.**
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> `/run/hyperhive` above all — it holds `host.sock`, the host **admin** socket.
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> Pointing nginx at that directory to reach this socket would put the admin
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> socket within its reach too.
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nginx is a host service, so nothing narrows what it can reach except the
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directory itself — that is the whole of the access control. A unit test pins
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the default path so a tidying edit fails instead of reviewing cleanly.
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`RuntimeDirectoryPreserve=yes` and the daemon's stale-socket unlink on start are
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a **pair**: preserving the directory without the unlink means `bind` fails with
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`EADDRINUSE` after a restart.
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## Packaging
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Built by the workspace derivation and extracted as its own package
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(`nix build .#swarm-controller`). Deliberately **not** in `nix/packages`'
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`daemonBins` — that list is the core stack and drives the bundle
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`services.hyperhive.c0re.package` points at, so folding this in would put a
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swarm-scoped service into every hive's closure.
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