Compares cloud_provisioned.spec (what we asked DO for) against the live
cloud_resources row (what DO actually has). Any divergence becomes an
operator-resolvable drift record.
cloud_drift table: one row per drifted field. status open/accepted/
reverted/stale. Partial unique index keeps at most one OPEN drift per
(resource, field); resolved rows are retained as history.
ArcadiaCloud.Drift context:
- detect_all/0 — sweeps every provisioned resource. Per field in spec,
resolves the actual value (top-level schema field first, then attrs),
compares with loose equality (stringified scalars; lists as sets so
JSON round-trips don't false-positive). Mismatches upsert a cloud_drift
row + emit a drift_detected event in the resource event log.
- close_stale_drift — an open drift whose field no longer mismatches
(fixed elsewhere) closes as "stale" on the next sweep.
- accept_drift/2 — the live value becomes the new desired-state: parent
cloud_provisioned.spec is updated, spec_version bumped, drift closed
"accepted". Revert (mutating live infra back to spec) is intentionally
NOT here — it needs a saga and lands with the droplet-resize work.
DriftDetectionWorker — Oban cron at :20 past the hour, offset past the
:15 resource syncs so it compares against fresh inventory.
Provisioning.record_provisioned/3 — populates cloud_provisioned desired-
state (upsert on resource_id, bumps spec_version). Future provisioning
sagas call this; for now it's how drift gets something to detect.
API (platform_admin only):
- GET /api/v1/drift — open drift inbox
- POST /api/v1/drift/:id/accept — adopt live value as desired-state
Smoke verified: recorded a droplet's desired spec with a deliberately
wrong size_slug + a correct region; detect_all flagged only size_slug,
wrote the drift_detected event; accept updated the spec to the live
value and closed the drift; re-detect found zero drift.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
DigitalOcean.Client write methods:
- create_droplet_snapshot/3 — POST a snapshot action (async)
- get_droplet_action/3 — poll action status
- list_droplet_snapshots/2 — snapshots for a droplet
- delete_snapshot/2 — DELETE (used by compensation)
All use the "provisioning" token purpose.
Steps.CreateDropletSnapshot — the first saga step that touches real
infra:
- execute: deterministic snapshot name (arcadia-snap-<droplet>-<saga8>);
checks context for a prior snapshot_id, then checks DO for a snapshot
already carrying that name (crash-between-post-and-save recovery),
then posts the action, polls to completion, finds the resulting
snapshot, records snapshot_id + snapshot_name in context.
- compensate: deletes the snapshot; treats HTTP 404 as success.
Provisioning.snapshot_droplet/2 — convenience saga starter.
Two DO eventual-consistency gotchas surfaced + handled:
- After a snapshot action reports "completed", the snapshot lags a few
seconds before appearing in /droplets/:id/snapshots. The step now
retries the lookup (find_snapshot_with_retry, 12x5s) instead of
failing with :snapshot_not_found_after_completion.
- Deletion has the same lag the other way — a deleted snapshot lingers
in the listing briefly. compensate just trusts the DELETE 2xx/404;
no post-delete verification needed.
Live smoke verified end-to-end against holyspiritbraypark.com:
[CreateDropletSnapshot, Fail] saga — the step created real snapshot
229305609, the Fail step triggered compensation, compensation deleted
the snapshot. Final: saga rolled_back, ledger
[create_droplet_snapshot: compensated, fail: failed], zero leftover on DO.
Test-harness note: smoke tests create sagas via Provisioning.create_saga
(no Oban enqueue) so a single manual Runner.perform/1 owns execution —
start_saga/1 enqueues an Oban job, and running both racing the same saga
corrupts the step ledger. Production only ever runs via Oban.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
The architectural spine of every write workflow phase 2+ — provisioning,
suspension, offboarding, updates, rollback — all ride this engine. Each
becomes a step list, not new orchestration code.
Schemas:
- saga_runs — kind, status (pending/running/completed/failed/
compensating/rolled_back), step_modules, current
step idx, accumulating context (jsonb), cancel
flag, error.
- saga_step_results — per-step audit ledger: status (running/completed/
failed/compensated), output, attempts, timings,
unique (saga_id, step_idx).
- cloud_provisioned — desired-state for resources WE provisioned. spec
+ spec_version + saga_id; FK to cloud_resources.
Phase 2's drift-detection diff lands here.
Step contract (ArcadiaCloud.Provisioning.Step):
- execute(state) -> {:ok, state} | {:error, reason}
- compensate(state) -> :ok | {:error, _} (optional)
- name() -> String.t()
SagaState carries the live execution state — accumulating context,
immutable inputs, current step_idx. Helpers: get_output/put_output
(context r/w), get_input (inputs read-only).
Runner (Oban worker, queue: provisioning, max_attempts: 1):
- kick_off: pending -> running, run_step(0)
- run_step: idempotent re-entry on saga.current_step_idx; persists step
result + saga context after each step; recursive forward walk through
the whole step list within one perform/1 call.
- safe_execute: try/rescue/catch around module.execute so a raised
exception triggers compensation rather than blowing up the worker.
- start_compensation: status=compensating, walk from idx-1 down to 0,
calling compensate/1 where it's exported; logs but doesn't halt on
compensate failure (best-effort + audit log).
- cancellation: checked between steps; cancel_requested=true -> trigger
compensation from current idx.
- crash recovery: max_attempts: 1 + run_step keyed on
saga.current_step_idx means Oban requeue picks up at the right place,
but full crash-resume infra is deferred to phase 2.5 (manual re-enqueue
works for now).
Two proof-of-concept steps (Steps.Echo, Steps.Fail) demonstrate the
engine without any DO API exposure. First real DO write step lands in
the next chunk.
Provisioning context provides start_saga/1, list_sagas/1,
list_step_results/1, cancel_saga/1, upsert_step_result/3.
Live smoke verified end-to-end:
- [Echo, Echo, Echo] happy path: all 3 completed, context accumulated
echoed_at_step_0/1/2 = "hello".
- [Echo, Echo, Fail] failure path: step 2 failed, compensation walked
back through step 1 then step 0; final status rolled_back with error
{compensate_from_idx: 1, reason: "step_failed:fail"}; ledger shows
echo/echo/fail with statuses compensated/compensated/failed.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
