78021ce982
Apply contraction fixes across ~40 doc files (setup, integrations, lifecycle, networking, scheduler, swarm, tools, trust-boundary, UI, etc.). Skipped 14 hits: - 10 where words appear in ALL CAPS for deliberate emphasis (is NOT, do NOT, etc.) - 4 where text could not be safely located due to markdown formatting or column position Applied via systematic scan with checks for fenced code blocks, inline code spans, and intentional caps. Preserves sentence-initial capitalization throughout.
224 lines
9 KiB
Markdown
224 lines
9 KiB
Markdown
# Snapshot store
|
|
|
|
The swarm's `btrfs receive` endpoint. Hives push agent snapshots to it
|
|
over the WireGuard mesh; a destination hive later pulls one back to
|
|
complete a migration.
|
|
|
|
Two things it's not, both worth stating because both are common
|
|
assumptions:
|
|
|
|
- **it's not the swarm controller**, and doesn't depend on one. it's
|
|
a NixOS host role: a btrfs subvolume tree, a socket-activated
|
|
receiver, and the `wg-hive` interface the swarm module already brings
|
|
up. that's why it can be deployed before any controller exists.
|
|
- **it's not a backup product.** It happens to hold the data a backup
|
|
would hold, and it should be operated accordingly (see
|
|
[Operating it](#operating-it)) --- but nothing in it does scheduling,
|
|
verification, or restore orchestration.
|
|
|
|
## Enabling it
|
|
|
|
```nix
|
|
services.hyperhive.snapshotStore = {
|
|
enable = true;
|
|
path = "/var/lib/hyperhive-snapshots"; # must be on btrfs
|
|
port = 51821;
|
|
};
|
|
|
|
# The mesh is a hard requirement, and is asserted:
|
|
services.hyperhive.deploy.wireguard = {
|
|
enable = true;
|
|
address = "10.100.0.9/24";
|
|
privateKeyFile = "/etc/wireguard/hive.key";
|
|
};
|
|
```
|
|
|
|
The store host is a swarm member like any other: it gets an entry in
|
|
`services.hyperhive.swarm.hives`, the same directory every host holds. See
|
|
[swarm/](../swarm/README.md) for the mesh itself.
|
|
|
|
Note that the mesh is gated on `deploy.wireguard.enable`, **not** on
|
|
`c0re.enable` --- a store host runs no hive and would otherwise get no
|
|
`wg-hive` interface at all.
|
|
|
|
## Pointing a hive at it
|
|
|
|
The block above configures the host that _receives_. Every hive that
|
|
_pushes_ separately needs to be told where the store is:
|
|
|
|
```nix
|
|
services.hyperhive.swarm.snapshotStore = {
|
|
address = "10.100.0.9"; # the store's mesh address, no prefix
|
|
port = 51821; # optional; must match the receiver's port
|
|
};
|
|
```
|
|
|
|
Two deliberate asymmetries in that pair, both liable to be misread as
|
|
inconsistency:
|
|
|
|
- **`address` has no default.** it's a deployment fact a pushing hive
|
|
can't derive, and a wrong guess means streaming an agent's state at
|
|
whatever happens to answer. Unset, a push fails naming this option.
|
|
- **`port` does default** (`51821`), because it's a convention both
|
|
ends read from the same option docs --- a default there is
|
|
coordination, not a guess.
|
|
|
|
Note the option lives under `swarm.*` while the receiving host's lives
|
|
under `services.hyperhive.snapshotStore`. that's the distinction the
|
|
two namespaces carry throughout: `swarm.*` describes _the swarm_ as seen
|
|
from this host, and a bare `services.hyperhive.<service>` describes _a
|
|
role this host performs_. A store host sets both --- one to run the
|
|
receiver, one only if it also runs a hive that pushes.
|
|
|
|
With it set, `hivectl agent <name> subvol snapshot push <label>
|
|
[--parent <label>]` streams a snapshot straight into the store. There is
|
|
no destination argument, because a swarm has exactly one store (see
|
|
[One subvolume per agent, not per hive](#one-subvolume-per-agent-not-per-hive)),
|
|
and no credential argument, because the mesh is the authentication.
|
|
|
|
## The mesh is the authentication
|
|
|
|
There are no certificates here, and no key material of its own. that's
|
|
deliberate rather than an omission.
|
|
|
|
WireGuard's cryptokey routing already binds a peer's source address to
|
|
its public key: the swarm module configures each peer with
|
|
`allowedIPs = [ peer.wireguardAddress ]`, so a packet arriving from
|
|
that address provably came from the holder of that private key. A
|
|
packet that reaches the receiver has therefore already been
|
|
authenticated by the kernel.
|
|
|
|
Layering TLS client certs on top would authenticate _the same fact_ a
|
|
second time, and add a credential with an expiry --- a migration that
|
|
fails because a renewal quietly didn't happen, discovered on the day
|
|
you need to move an agent.
|
|
|
|
## One subvolume per agent, not per hive
|
|
|
|
The destination is keyed by **agent**.
|
|
|
|
This isn't cosmetic. After a migration, an agent's next incremental
|
|
send arrives from a _different_ hive than the previous one. Keying by
|
|
hive would split that agent's snapshot chain across two directories,
|
|
and `btrfs send -p` would fail to find its parent --- breaking exactly
|
|
the case the store exists to serve.
|
|
|
|
## What the sender can and can't choose
|
|
|
|
A `btrfs send` stream carries no notion of _which agent_ it belongs to,
|
|
and the subvolume name inside it's chosen by the sender. So the
|
|
protocol is one `agent <name>` header line, then the raw stream.
|
|
|
|
The rule that matters:
|
|
|
|
> **The receiver owns the destination root. The sender-supplied name is
|
|
> validated, never used as a path.**
|
|
|
|
Validation is an allowlist --- `[A-Za-z0-9_-]+` and nothing else. No
|
|
slash and no dot means neither directory traversal nor an absolute path
|
|
can survive it. it's deliberately an allowlist and not a list of
|
|
forbidden characters: a blocklist only ever excludes the attacks
|
|
somebody already thought of.
|
|
|
|
## Reachability
|
|
|
|
The receiver is socket-activated, and the socket binds **this host's
|
|
mesh address**, never a wildcard. Both the mesh being enabled and the
|
|
address being set are assertions, not documentation --- bound to
|
|
`0.0.0.0` this socket is an unauthenticated remote write into agent
|
|
state.
|
|
|
|
Binding isn't sufficient on its own. NixOS's firewall is default-deny
|
|
and filters in netfilter, _before_ a packet reaches a bound socket, so
|
|
the port is opened explicitly --- and scoped to the mesh interface:
|
|
|
|
```nix
|
|
networking.firewall.interfaces.wg-hive.allowedTCPPorts = [ cfg.port ];
|
|
```
|
|
|
|
A host-wide `allowedTCPPorts` would open the port on every interface
|
|
including a public NIC, leaving only the socket's bind address between
|
|
the internet and a root `btrfs receive`.
|
|
|
|
## Operating it
|
|
|
|
### Confinement is the deployment's job
|
|
|
|
`btrfs receive` needs `CAP_SYS_ADMIN`, so the receiver runs as root.
|
|
The unit sets `ProtectSystem=strict`, `ProtectHome`, `PrivateTmp` and a
|
|
narrow `ReadWritePaths` --- but those are **defence in depth, not a
|
|
boundary**: a process holding `CAP_SYS_ADMIN` can call `mount(2)` and
|
|
undo the namespace they set up.
|
|
|
|
The boundary is the machine. The intended deployments are:
|
|
|
|
- **a swarm**: the store is its own small VM. The machine is the
|
|
boundary, which is stronger than anything the unit could assert about
|
|
itself.
|
|
- **all-in-one / local**: the store runs as a container on the c0re
|
|
host.
|
|
|
|
The second is worth keeping deliberately, and not only for
|
|
convenience: it means the confined path is exercised by every local
|
|
deployment. The usual failure mode for an isolated variant is that
|
|
nobody runs it day to day, so it rots and is discovered broken in
|
|
production.
|
|
|
|
⚠️ **The assumption to keep true over time:** the store host runs
|
|
nothing else. that's true on day one and quietly false the day someone
|
|
notices the box has spare disk. Nothing in the config objects when it
|
|
stops being true.
|
|
|
|
### It holds every agent's state from every hive
|
|
|
|
Which makes it the highest-value target in the swarm by a wide margin,
|
|
and means it should get the treatment a backup host gets --- restricted
|
|
access, and a decision (rather than an omission) on encryption at rest.
|
|
|
|
The trap is the label: this box holds backup-grade data while not being
|
|
called a backup, so it can end up with backup-grade _exposure_ and
|
|
non-backup-grade _controls_. Nobody puts a migration staging area on
|
|
the access-review list.
|
|
|
|
### What a snapshot contains
|
|
|
|
The snapshot covers an agent's **state subvolume**, which is the parent
|
|
of `state/`, `claude/` and `harness/` (see
|
|
[`docs/agent-lifecycle/persistence.md`'s btrfs subvolume
|
|
section](../agent-lifecycle/persistence.md#btrfs-subvolumes-for-varlibhyperhiveagentsname)
|
|
for how and when that subvolume is created). Consequences:
|
|
|
|
- The Claude session (`claude/`) travels, so a restored agent keeps its
|
|
live `--continue` session rather than needing to log in again.
|
|
- `harness/` travels too, including `harness/bash-tasks/`. Task output
|
|
is part of an agent's working continuity, so this is wanted --- but it
|
|
means anything that has ever leaked into a task's captured output is
|
|
in the retained snapshots as well.
|
|
|
|
It does **not** cover the agent's applied config (`/applied/<name>/`) or
|
|
its topology entry, both of which live outside the subvolume. A restore
|
|
therefore yields an agent's memory without its definition; closing that
|
|
gap is tracked separately.
|
|
|
|
### Retention
|
|
|
|
Retention lives on the _sending_ side (last-N by count, swept
|
|
periodically), not here. Count rather than age is deliberate: a count
|
|
is bounded by construction, whereas an age policy silently scales disk
|
|
usage with how hot a hive runs.
|
|
|
|
Per-agent or per-hive `btrfs qgroup` quotas aren't configured yet.
|
|
Without them one runaway hive can fill the store and take out every
|
|
other hive's snapshots.
|
|
|
|
## Not built yet
|
|
|
|
**The pull side.** Push is safe with minimal authorisation because a
|
|
hive can only ever write to a chain it owns. Pull is the direction that
|
|
needs a policy: unrestricted, any compromised hive could read every
|
|
agent's state from every other hive. It needs a notion of which hive
|
|
currently owns which agent, and that ownership record lands with the
|
|
swarm controller work.
|
|
|
|
With a single hive the question is trivial --- the only peer owns
|
|
everything it sends --- which is why the receive half ships first.
|