# Deployment

What running this safely requires. [The shape of the system](architecture.md)
draws the same hosts; this page states the rules.

## What runs

**A container image, started by one systemd unit, on one instance.** Not a
binary and a unit file; not an orchestrator. `scripts/` is a developer's
interface and no part of a deployment.

The image is built from the repository's `Dockerfile` with `--features
route53`, tagged with the release it holds, and pushed to ECR.
`infra/templates/user_data.sh.tftpl` writes `/etc/systemd/system/
didbot-pds.service` at first boot, substituting the image reference and the
deployment's zone, owner and hosted zone id directly into the unit — so
`systemctl cat didbot-pds` shows exactly what is running, with no environment
file to also go read.

Three properties decide this, and each of them is a property of the process
rather than a preference:

- **The unit must be a single-writer service.** The store is one write-ahead
  log behind one lock, and two live writers interleave frames neither can
  replay. `infra/ec2.tf` is one instance, not an autoscaling group; the unit
  runs the container under a fixed `--name` with an `ExecStartPre` that
  removes a previous one, so a restart racing a slow shutdown cannot produce
  two. Systemd is not the only way to start a process on a host, so the
  exclusion does not rest on it: `didbot_pds::lock` takes an exclusive
  `flock` on `pds.lock` inside the data directory before the log is opened,
  and an operator running the binary by hand against the mounted volume is
  refused by name. The kernel releases the lock when the process dies, so a
  crash leaves nothing to clean up.
- **The image is a name that can be said.** The exit criterion for
  [deploy](../plan/deploy.md) is that *a tagged release* runs on a host
  nobody develops on. A container digest is that name, and a `git pull` on
  the instance is not.
- **The process binds 443 and holds its own certificate.** Nothing terminates
  TLS in front of it, so the run unit uses `--network host` rather than a
  published-port mapping — which is also what lets the container's IMDSv2
  request reach the metadata endpoint at `http_put_response_hop_limit = 1`.
  Raising that to 2 is required if the run unit ever leaves host networking.
  The image runs as an unprivileged user, and with the host's network
  namespace there is no `net.ipv4.ip_unprivileged_port_start` to relax, so
  the binary carries `cap_net_bind_service=+ep` — one capability, bind a low
  port — rather than the container running as root.

Restarts are `Restart=on-failure` with `RestartSec=5`, capped at five failures
in two minutes so a crash loop stops rather than burning the instance. A
restart is not free: `didbot_pds::session::SessionAuth` is in-process memory,
so every outstanding access and refresh token is invalidated by one — see
"say what a restart does" in [deploy](../plan/deploy.md).

## The zone

One zone, used for everything: the server, the agent handles, the authority
serving every `did.json`, and the zone named in the owner's ownership record.
HTTPS throughout.

The server sits at the apex and agents in a subzone beneath it. Agents are off
the apex so a wildcard certificate cannot shadow the server's own name. The
zone does not have to sit at or below the server's own hostname — which server
serves a given agent is answered by resolving the agent's DID document, not by
comparing hostnames — but the recommended layout keeps them together.

Two hostnames per account — one for the DID, one for the handle — and both must
resolve before the account exists.

**One wildcard record makes both of them resolve.** The zone holds three names
whatever the account count: the apex, `*.<zone>`, and `_acme-challenge.<zone>`
while a certificate is being issued. Provisioning writes no record of its own —
`WildcardDns` is the provider for a zone in this shape, and it publishes
nothing because the wildcard already answers. [The names an agent
has](names.md) works one account through the whole path, from what exists in
the zone to what a stranger reads.

The cost is that there is no per-name existence guarantee and no DNS-level
garbage collection: a name no account holds still resolves, and answers 404
rather than `NXDOMAIN`. That is the correct trade here — DNS removal was never
a revocation mechanism, since a withdrawn name stays cached downstream for its
TTL, and an HTTP status is the only thing that can express a soft-deleted
account still serving its document.

A deployment can still publish per-agent records instead; `Route53Dns` does. It
buys the per-name existence check, and it costs a hosted-zone record per
retained account, a network call on the provisioning path, and — because a real
record at a name stops the wildcard synthesizing anything beneath it — any
prospect of hostnames deeper than one label.

## The DNS credential

Control of the zone is control of every name in it. It is as powerful as the
signing keys, and it lives beside them: the server writes the
`_acme-challenge` TXT records its certificate depends on and the `CAA` record
below, so the credential has to be reachable from the process. Under a
wildcard those are the only records it writes on an ordinary day — agent
hostnames cost none, and zone creation is refused unless
`dns.may_create_zones` turns it on. Holding it elsewhere would protect
nothing: whoever holds this host holds the signing keys, and with those they
can sign as any account it serves.

So the question is not where the credential sits. It is what it reaches, and
what a holder of it can be caught doing.

### What it can do

Precisely, for the one hosted zone it is scoped to:

- **Point any name in the zone somewhere else.** A specific record at a name
  overrides the wildcard, so a live agent's two hostnames — the DID's and the
  handle's, whose `/.well-known/atproto-did` is what binds the two together —
  can be made to answer from another host, which then serves its own
  `did.json`. `did:web` has no history. A document swapped today changes what
  every signature that account ever made verifies against, retroactively, and
  nothing an observer kept proves what the document said yesterday.
- **Point the server's own hostname somewhere else**, when the zone contains
  it. That is every route, every handle answer, and the certificate for it.
- **Pass DNS-01 for any name in the zone**, including names no account holds,
  and obtain a publicly trusted certificate that validates. An impersonation
  built on either of the two above survives TLS.
- **Rewrite the `CAA` record**, which is the step that makes the one above
  reachable through an authority other than the one this zone authorises.

Serving a document at a name this server never minted is not on that list, and
it is worth saying why: under a wildcard every name in the zone already
resolves here without any DNS write at all. What answers at one is this
server's business, not DNS's — which is why a name no account holds answers
404 rather than `NXDOMAIN`, and why a zone that does publish per-agent records
gets a per-name existence check the wildcard cannot give.

What it does not reach is anything outside that one hosted zone — not other
zones in the account, and not the `NS` records at the registrar that delegate
into this one, which live in the parent zone. That boundary is the IAM policy
below and nothing else, which is why the policy is the load-bearing part.

### What is detectable

Detection is what bounds a compromise here, because isolation cannot. Three
channels, and they differ in the one way that matters — whether the evidence
is somewhere the holder of this host can reach.

**Certificate transparency.** Every publicly trusted certificate is logged by
the authority that issued it, to logs this deployment does not run. A
certificate naming any hostname in the zone that this server did not order is
visible there, and only there: no record of it exists on this host, and
nothing about the issuance touched it. Subscribe an external monitor to the
zone. This is the one channel a compromised host cannot suppress, and it is
after the fact — the certificate already exists when the log entry appears.

**A refused issuance, reported by the authority.** The `CAA` record the
server publishes at the zone apex names one authority and, per RFC 8657's
`accounturi`, the one ACME account at it this deployment holds the key for.
An attempt to issue for a name in this zone through any other account is
refused by any authority honouring the record, and reported to the `iodef`
contact in it — a report that arrives from the authority, not from this host.
This does not stop the holder of the zone credential, who can rewrite the
record. It makes doing so a second, separate act, and it closes issuance to
everyone who does not hold the credential.

**A zone holding a record nobody here wrote.** `ListResourceRecordSets` says
what the zone actually contains, and this server knows what it put there. A
wildcard zone makes that check almost trivial — it holds the apex, `*.<zone>`
and `_acme-challenge.<zone>`, and a fourth name is a name somebody else
added. A zone publishing per-agent records checks the same thing against the
ledger, which keeps a name past the account it described. Either way this is
observed on the host holding the credential, so it proves nothing against an
attacker who holds it; what it catches is a credential copy still live
somewhere, a second stack writing the same zone, or a change made by hand in
a console. Nothing runs the comparison today — `Route53Dns::resync` already
reads every record set in the zone, and no code diffs what it finds against
what this server expects; see `plan/agent-accounts.md`.

### What is not recoverable

Rotating the credential and rewriting the zone recovers the zone. It does not
recover any of the following, and no procedure does:

- **Confidence in anything signed before the compromise was noticed.** A
  swapped `did:web` document leaves no trace of the key it replaced. A record
  signed by the agent and a record signed with the substituted key are
  indistinguishable afterwards, in both directions — the compromise does not
  only forge new records, it makes the real ones unprovable.
- **Whatever resolved during the window.** A repointed name was cached by
  every resolver that asked, and served to every client that followed it.

A certificate is the exception: an issued certificate can be revoked, and the
authority that issued it is who to ask.

### The policy that bounds it

`crates/didbot-dns`'s `Route53Dns` is the provider that scopes this: an IAM
credential given only

```text
route53:ChangeResourceRecordSets, route53:ListResourceRecordSets
  on arn:aws:route53:::hostedzone/<HOSTED_ZONE_ID>
route53:GetChange
  on arn:aws:route53:::change/*
```

can write and read records in the one hosted zone this server owns, and
nothing else in the account. `GetChange` has to be unscoped to a zone because
Route53 change ids are not namespaced under one; it grants read of a change's
propagation status, not write of anything. A cloud DNS service is the right
kind of provider for exactly this reason — the credential narrows to a single
zone — and across several servers that narrowing is the blast-radius boundary
between them. See the module docs on `Route53Dns` for the full policy JSON
and for how it handles eventual consistency, rate limits and hosted-zone
record limits, all things this posture note assumes are handled correctly one
layer down.

The boundaries this design actually rests on are elsewhere, and neither is
inside this host: the agent hosts are separate machines from this one, and the
policy that governs it lives in a repository this server holds no credential
for. A compromised server can break policy; it cannot change it.

## Certificates

The server terminates TLS itself. Nothing in front of it holds a certificate,
so it obtains and renews its own over ACME DNS-01, through the same zone
credential above (`crates/didbot-tls`, on `instant-acme`).

**One `<zone>` + `*.<zone>` pair per configured zone.** A wildcard *in a
certificate* matches exactly one label: `*.pds.did.bot` covers
`claudes.pds.did.bot` and does not cover `agent.claudes.pds.did.bot`. This is
not the DNS rule — a wildcard *record* of the same spelling answers at any
depth — so what bounds how deep an agent hostname may sit is the certificate,
not the zone. See [the names an agent has](names.md). A deployment configured with
`claudes.pds.did.bot` and `vllm.pds.did.bot` therefore holds two
certificates, each from one ACME order carrying both of that zone's
identifiers — the apex and the wildcard — whose two DNS-01 challenges share
one `_acme-challenge.<zone>` record and must be published together.
`didbot_tls::fleet::CertificateFleet` holds one manager per zone and
`ZoneResolver` picks between their certificates on the SNI name each
handshake carries. A name no configured zone covers is refused rather than
handed a certificate that does not name it.

**A renewal never rebinds the listener.** The certificate lives behind an
`ArcSwap` that `rustls` reads once per handshake, so a renewal is a pointer
store: connections already established — the firehose relays and indexers
hold open for hours — are untouched, and the next handshake sees the new
certificate.

**A failed renewal keeps serving what it has, and gets louder.** Renewal
starts 30 days before expiry and retries hourly; every failure leaves the
current certificate in place and is logged with the zone, the failure count
and the expiry it is measured against. Three consecutive failures raise that
zone to `Warning`; inside three days of expiry it is `Critical` whether or
not anything has failed, because at that point expiry itself is the risk.
`CertificateFleet::alert_level` reports the worst level any zone is at and
`zone_alert_levels` says which zone it came from. Nothing pages on this yet —
see "alert on the things that fail quietly" in [deploy](../plan/deploy.md).
An expired certificate is a total outage for every hostname in that zone,
agents included.

**The zone's `CAA` record is written by the server, on every start.** It is
published before the first order and restated on each start, naming the
authority the order is about to go to and the ACME account the order will be
placed through — `didbot_tls::dns::IssuancePolicy`, reading both off the live
objects rather than off configuration. That is deliberate: a `CAA` record
naming an account this deployment cannot use does not fail safe, it stops the
next renewal, and an expired certificate is a total outage for every hostname
in the zone. Reading both halves from the objects the order itself uses makes
that disagreement unreachable. A backend whose zone already says exactly this
skips the write. There is no `issuewild` property — RFC 8659 falls back to
`issue` for a wildcard request when none is present, and the wildcard is in
the same order — and failing to publish the record is a warning rather than a
startup failure, because a zone with no `CAA` record is the state every zone
starts in.

**The server is handed the zones it may write.** Each zone needs a hosted
zone id configured for it (`--route53-zone-id <zone>=<id>`); a zone without
one publishes nothing and says so at startup. Creating a hosted zone, or
delegating a new one with `NS` records in the zone above, is a separate
posture — `dns.may_create_zones` in `didbot-config` — and is off by default.

## The data directory

One directory, `--data`, on a volume separate from the root volume so an AMI
upgrade or an instance resize can re-attach it rather than lose it. The
instance mounts it at `/data` and the container sees `/data/pds` as `/data`.

| Path | Holds | Mode |
|---|---|---|
| `pds.wal` | The log: accounts, records, ledger, commits, name holds — and the account signing keys | `0600` |
| `pds.wal.compact` | A compaction's scratch file, replaced by rename | `0600` |
| `pds.lock` | The single-writer claim on this directory | `0600` |
| `pds.layout` | Which log shape wrote this directory | `0600` |
| `blobs/` | Blob content, addressed by CID | `0700` |
| `blobs/.incoming/` | Uploads in flight, discarded on restart | `0700` |
| `tls/` | The ACME account key | `0700` |
| `tls/zones/<zone>/` | That zone's certificate, its key, and issuance metadata | `0700` |

Everything else a deployment has — configuration, the e-stop file and socket —
is elsewhere and is not state.

**Permissions are set on every open, not only on creation.** The signing keys
are in `pds.wal`, so the directory holding it is only as private as whoever
made it. A directory the server creates is `0700` from `DirBuilder::mode`; a
directory it was handed — an operator's `mkdir`, a mount point, a restored
snapshot's filesystem root — carries whatever umask made it.
`didbot_pds::wal::create_dir` therefore `chmod`s an existing directory to
`0700` every time it runs rather than trusting it, and
`didbot_tls::storage::create_dir` does the same for `tls/`. That costs one
syscall on the common path and closes the case that actually matters.

What it does not fix is ownership. A directory owned by another user is not
made safe by its mode, and the server does not check: it will fail to write
and say so, which is correct but is a boot failure rather than a diagnosis.
Ownership is the boot script's. The image runs as uid **10001**, pinned in
the `Dockerfile` rather than left to `useradd`, and
`user_data.sh.tftpl` chowns `/data/pds` to that uid before the unit starts —
which also re-homes a restored snapshot whose files were written by a
different uid.

## Secrets, and where each lives

Three, and the process holds all three itself:

| Secret | Lives | Reachable as |
|---|---|---|
| Account signing keys | `pds.wal`, inside the data directory | The file, `0600` |
| The ACME account key | `tls/acme-account.json` and the certificate keys under `tls/zones/` | The file, `0600` |
| The Route53 credential | Nowhere on disk | The instance role, over IMDSv2 |

The DNS credential is the only one that is not a file, and deliberately: the
instance profile in `infra/iam.tf` grants
`ChangeResourceRecordSets`/`ListResourceRecordSets` on the one hosted zone and
`GetChange` unscoped, and the AWS SDK reads short-lived credentials for that
role from the metadata endpoint. Nothing is passed on the unit's command line
and nothing is fetched into a file at boot.

The owner's DID is on the command line, not here. It is an identifier, not a
credential — this server holds nothing that lets it write the owner's
repository, which is the whole reason policy can constrain it.

**What one compromised host gets an attacker: all three.** They are on one
box by design, and there is no ordering that changes the answer — the keys
sign as any account the server serves, and the zone credential extends that to
names it has never minted. Separating the credential from the keys is not a
mitigation here and is not offered as one: it has to be reachable from this
process to write DNS-01 challenges, so whoever holds the process holds it.
What bounds a compromise instead is scope and detection, and [the DNS
credential](#the-dns-credential) above states both.

## Backups and restore

`infra/backup.tf` puts the data volume under an AWS Backup plan: daily at
09:00 UTC, snapshots kept thirty days. The volume is the whole of the state —
the log and the blobs are both on it — so one snapshot is one consistent
deployment, give or take writes in the seconds around it.

**A restore recovers accounts, records, blobs, name holds and ledger
history**, because those are the log. It recovers the signing keys with them,
which is what makes the restored accounts the *same* accounts rather than new
ones with the same handles.

**A restore does not recover four things, and each fails differently:**

- **Sessions.** Every access and refresh token is in-process memory. A restore
  is a restart, so every signed-in client is logged out, and the failure is
  indistinguishable from a revoked session.
- **The DNS zone.** Snapshots are of a volume, not of Route53. A zone that was
  also lost has to be recreated and re-delegated at the registrar before any
  hostname resolves, and the restored server's records are written by the
  server itself once it is running.
- **A usable certificate.** `tls/` is on the volume, so a certificate restored
  within its validity is served immediately. One restored from a snapshot
  older than the certificate is expired, and the server will re-issue over
  ACME DNS-01 — which needs the zone above to be working first, and is subject
  to the issuer's rate limits on a name that has been issued repeatedly.
- **Anything written since the snapshot.** Up to twenty-four hours of accounts
  and records. There is no point-in-time recovery here and no log shipping.

**The restore drill.** Nobody has run it, so it is not yet a backup:

1. Create a volume from a recovery point in the `didbot-pds` vault, in the
   instance's availability zone.
2. Attach it to a *fresh* instance — never to the running one; two mounts of
   one log is the corruption `pds.lock` exists to refuse.
3. Mount it and run `didbot-dev --data <mount>/pds` against a development
   zone.
4. Confirm the accounts that should be there are there: `bot.did.listAgents`
   returns the expected count, one agent's `did.json` resolves out of the
   restored keys, and a blob that account referenced fetches back byte for
   byte.
5. Detach and delete the test volume.

Step 4 is the whole drill. A snapshot that attaches and mounts proves the
filesystem, not the log. Until someone has run this against real
infrastructure, the item stays open.

## Where to run it

One server serves many agent hosts. Agents are grouped, and a compromise of one
host does not reach the others.

| Posture | A compromised agent reaches |
|---|---|
| Server and agents on one laptop | Everything: keys, zone credential, every account, and the operator's own logins beside them. |
| Server in the cloud, agents on a laptop | That laptop's session credentials, its node credential, and the ability to mis-stamp identity for later sessions there. |
| Server in the cloud, agents in cloud sandboxes | One sandbox, for as long as it lives. |

The first row is the development posture. The step to the second is the one
that matters and the cheapest: it moves the keys and the zone credential off
the machine running agent code. The third also makes browser isolation moot —
one sandbox per session is one browser profile per agent — and allows
instance-identity attestation, which is stronger evidence than a credential
file on a shared host.

Agents are capable and sandboxing between them is not guaranteed. Separating
agent hosts from the server host is achievable; separating agents from each
other on one host is not. Record what cannot be enforced.

## Configuration tiers

| Tier | Holds | Reachable on the host |
|---|---|---|
| The owner's repository | What an agent may hold: ceilings, admitted apps, collection permissions | No |
| Process arguments and the configuration file (`didbot-config`, see [config](../plan/config.md)) | How the server runs: bind address, zone, state directory, blob and disclosure settings, which DID's policy to read | Yes |
| Local state | Caches, refusal records, the emergency stop | Yes |

Nothing below the owner's repository may widen what an agent may do. The
management surface is not a replacement for configuration: what the process
needs in order to start is an argument, and what an agent may do is a record
somewhere else.

## Clocks

An attestation claim is valid inside a window. A host with a wrong clock cannot
provision, and the failure does not look like a clock problem.