svcforge/services/worker/handlers.py

"""Task handlers.

Every handler obeys one rule: running it twice must equal running it once.

A worker can be SIGKILLed after helm installed the release but before the DB row says so;
the lease expires, another worker claims the same task, and this function runs again. A
handler that is not idempotent gives the tenant two Elasticsearches and you a bill.
Idempotency is bought in two places: a deterministic `release_name`, and adapters that
state desired state (`helm upgrade --install`) instead of issuing imperative commands.
"""

from __future__ import annotations

from collections.abc import Awaitable, Callable
from typing import Any

from services.worker.deps import WorkerDeps
from svcforge_core.domain.models import CatalogEntry, Instance, Task, TaskKind
from svcforge_core.domain.states import InstanceState
from svcforge_core.errors import SvcforgeError
from svcforge_core.obs import get_logger
from svcforge_core.repo.instances import INSTANCE_COLUMNS

log = get_logger("svcforge.worker")


class HandlerError(SvcforgeError, RuntimeError):
    """A task failed in a way worth retrying. The message lands in tasks.last_error."""


async def _load_instance(task: Task, deps: WorkerDeps) -> Instance:
    async with deps.pool.connection() as conn, conn.cursor() as cur:
        await cur.execute(
            f"select {INSTANCE_COLUMNS} from instances where id = %s",  # noqa: S608 - module constant
            (task.instance_id,),
        )
        row = await cur.fetchone()
    if row is None:
        raise HandlerError(f"instance {task.instance_id} vanished")
    return Instance.model_validate(row)


def _values_for(inst: Instance, entry: CatalogEntry) -> dict[str, Any]:
    """Turn a catalog size into helm values."""
    size = entry.sizes.get(inst.size)
    if size is None:
        raise HandlerError(f"size {inst.size!r} not in catalog for {inst.service_type!r}")
    return {"replicaCount": size.replicas, "resources": size.resources}


async def handle_provision(task: Task, deps: WorkerDeps) -> None:
    """Install the release and mark the instance ready. Idempotent."""
    inst = await _load_instance(task, deps)

    if inst.state is InstanceState.READY:
        # A previous attempt already finished; the crash was after the work, before the
        # bookkeeping. Nothing to do — and re-installing would be the bug.
        return

    entry = deps.catalog.get(inst.service_type)
    if entry is None:
        raise HandlerError(f"unknown service_type {inst.service_type!r}")

    # Best-effort CAS. It returning False means someone else moved the row; the helm call
    # below is idempotent either way, so this is bookkeeping, not a lock.
    await deps.instances.update_state(inst.id, InstanceState.REQUESTED, InstanceState.PROVISIONING)

    await deps.provisioner.install(
        release=inst.release_name,
        ns=inst.namespace,
        entry=entry,
        values=_values_for(inst, entry),
    )

    endpoint = f"http://{inst.release_name}.{inst.namespace}.svc.cluster.local"
    ok = await deps.instances.update_state(
        inst.id, InstanceState.PROVISIONING, InstanceState.READY, endpoint=endpoint
    )
    if ok:
        try:
            await deps.notifier.send(
                "instance.ready",
                f"instance {inst.id} is ready at {endpoint}",
                {"instance_id": str(inst.id), "team": inst.team, "service_type": inst.service_type},
            )
        except Exception:
            # The provision succeeded and the row is READY; the notification is a courtesy.
            # Propagating a webhook timeout would fail the task, and the retry would hit the
            # READY early-return and drop the notification anyway — so a flaky notifier
            # would turn every provision into a "failed" task.
            log.exception("notify.failed", instance_id=str(inst.id))


async def handle_deprovision(task: Task, deps: WorkerDeps) -> None:
    """Remove the release and mark the instance deleted. Idempotent."""
    inst = await _load_instance(task, deps)

    if inst.state is InstanceState.DELETED:
        return

    # `helm uninstall` of an already-gone release is not an error to us: the adapter
    # swallows not-found, because the desired state — no release — is already true.
    await deps.provisioner.uninstall(release=inst.release_name, ns=inst.namespace)

    # Raise rather than ignore the CAS result. Swallowing it leaves the release gone, the
    # row on `state=ready` with a dangling endpoint, the task marked done — and 60 seconds
    # later the drift check re-provisions the thing the tenant asked to delete.
    if not await deps.instances.update_state(inst.id, InstanceState.DELETING, InstanceState.DELETED):
        raise HandlerError(
            f"instance {inst.id} was {inst.state.value}, expected {InstanceState.DELETING.value}"
        )


async def handle_upgrade(task: Task, deps: WorkerDeps) -> None:
    """Upgrade the release to the catalog's pinned version, then record it.

    `instances.chart_version` is written only AFTER helm reports success. That column is
    what the day-2 work-list query compares against, so writing it optimistically would
    make the fleet look upgraded while it isn't.
    """
    inst = await _load_instance(task, deps)
    entry = deps.catalog.get(inst.service_type)
    if entry is None:
        raise HandlerError(f"unknown service_type {inst.service_type!r}")

    if inst.chart_version == entry.chart_version:
        return  # already there

    await deps.provisioner.install(
        release=inst.release_name,
        ns=inst.namespace,
        entry=entry,
        values=_values_for(inst, entry),
    )

    async with deps.pool.connection() as conn, conn.cursor() as cur:
        await cur.execute(
            "update instances set chart_version = %s, updated_at = now() where id = %s",
            (entry.chart_version, inst.id),
        )


async def handle_verify(task: Task, deps: WorkerDeps) -> None:
    """Post-upgrade health probe. On failure, halt the whole rollout for this service type.

    The work-list query returns nothing while `rollout_state='halted'`, so a bad chart stops
    after the first tenant instead of all of them. Clearing it is a deliberate SQL statement:
    an automatic un-halt would resume breaking things.
    """
    inst = await _load_instance(task, deps)
    releases = {r.name for r in await deps.provisioner.list_releases()}

    if inst.release_name in releases:
        return

    # `returning` plus a `where` on the update half says whether THIS call halted the
    # rollout. The halt is idempotent; the page is not. Without the distinction, a verify
    # that burns its full retry budget sends five identical notifications for one incident.
    async with deps.pool.connection() as conn, conn.cursor() as cur:
        await cur.execute(
            """insert into catalog_versions (service_type, rollout_state)
                    values (%s, 'halted')
               on conflict (service_type) do update set rollout_state = 'halted'
                     where catalog_versions.rollout_state <> 'halted'
               returning service_type""",
            (inst.service_type,),
        )
        newly_halted = await cur.fetchone() is not None

    if newly_halted:
        await deps.notifier.send(
            "rollout.halted",
            f"rollout halted for {inst.service_type}: {inst.release_name} failed verify",
            {"instance_id": str(inst.id), "team": inst.team, "service_type": inst.service_type},
        )
    raise HandlerError(f"verify failed for {inst.release_name}; rollout halted")


HANDLERS: dict[TaskKind, Callable[[Task, WorkerDeps], Awaitable[None]]] = {
    TaskKind.PROVISION: handle_provision,
    TaskKind.DEPROVISION: handle_deprovision,
    TaskKind.UPGRADE: handle_upgrade,
    TaskKind.VERIFY: handle_verify,
}