55 lines
2.3 KiB
Markdown
55 lines
2.3 KiB
Markdown
# `backup_store`
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Pulls already-encrypted backup artefacts from every source host onto
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`small-backups-box`, on a timer, and expires them per source.
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Generalises the hand-written `pull-backups.sh` that had one hardcoded source
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(`arbret`). That job's behaviour is preserved exactly: same source path, same
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90 days, same destination directory.
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## This host holds no key
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Everything pulled here is ciphertext produced by `backup_source` on the source
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host. The box cannot read any of it — the age identity lives only on lapy. That
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is deliberate: the machine holding every backup should not also be able to open
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them.
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## One failing source must not stop the others
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The script is `set -uo pipefail`, **not** `-e`. Each source runs in its own
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function, failures are counted, and the script exits non-zero at the end so
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systemd marks the unit failed. A dead host costs you that one source, not the
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whole run.
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This is the specific failure the whole plan exists to prevent: the laptop jobs
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aborted on first error and then silently produced empty directories for nine
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months.
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## Trust points one way
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The box authenticates with `~/.ssh/id_pull` to an unprivileged, dedicated
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account on each source (`backup-pull`, or `arbret` on prd-arbret), authorised
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with `restrict`. That account can read one directory and do nothing else — no
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sudo, no pty, no forwarding. A compromised backup box cannot reach into
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production.
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## Addressing: names, never IPs
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Sources are addressed by name. The job this replaced hardcoded spacey's IP; the
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droplet was later rebuilt, the address was recycled to a stranger, and the
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backup failed silently from 2025-12-01 while the directory listing still looked
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healthy.
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Two kinds of name are in play:
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- **Tailnet members** (vipy, memos-box, …) → MagicDNS names. These require a
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headscale ACL grant from `tag:small-backups-box` to the source's `:22`; without
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it the box cannot even resolve the peer, let alone reach it.
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- **spacey** is *not* a tailnet member — it is the headscale control server — so
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its backup is pulled over the public internet via `headscale.contrapeso.xyz`,
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which follows the host if the droplet is rebuilt.
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## Retention here is the long tail
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Sources keep a few days locally; this box keeps 90 (or whatever the source entry
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says). Losing the source's local copy is expected.
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