arkitekt-service

What a service of an Arkitekt hub is made with. Three parts, for three different things a service process does:

They share arkitekt_service.trust — no secrets between services: every instance signs with its own key and the hub vouches for the public halves — and nothing else. A process uses any of them without the others.

pip install arkitekt-service

The contract

Every service image answers the same entry point:

python -m arkitekt_service describe    # what it needs from a hub and offers to it (JSON)
python -m arkitekt_service render      # this release's config, from the hub's facts
python -m arkitekt_service check       # does this release read a config as written?
python -m arkitekt_service migrate     # its database migrations, as a step
python -m arkitekt_service upgrade --from 5.2.0 --to 6.0.0

An installer (Konstruktor) then needs to know the hub, and nothing about a service that the service's image does not say. How a release spells its config, which keys it renamed, what it has to do to its data — all of that ships in the image, with the code it belongs to. Exit code 78 is a release's own refusal (facts it cannot be configured from, a setting it does not read), with the reason on stderr.

A service declares itself in one module, named by ARKITEKT_SERVICE in its Dockerfile:

from arkitekt_service.contract import JSON, Contract, Description, Facts, Needs, Offers, blocks


def render(facts: Facts) -> dict[str, JSON]:
    document = blocks.server(facts)  # django, postgres, redis, authentikate
    document["datalayer"] = blocks.datalayer(facts, "media", "zarr")
    return document


contract = Contract(
    description=Description(name="mikro", needs=Needs(storage=["media", "zarr"])),
    settings=Settings,
    render=render,
)

The hub's facts (arkitekt_service.contract.facts) and a service's description (arkitekt_service.contract.description) are versioned documents; an image refuses facts it does not understand rather than dropping them.

A service, and a hook agent

from arkitekt_service.service import Descriptor, Service, organization_of
from arkitekt_service.hook import HookAgent

service = Service("mikro", description="Microscopy data")
dataset = service.structure(ArrayDataset, "@mikro/arraydataset", descriptors=[Descriptor("@mikro/n_channels", "INT")], describe=array_descriptors)
service.model_signal(dataset, organization=organization_of())

agent = HookAgent("mikro", description="mikro's housekeeping")


@agent.action
def reembed_stale(organization: str) -> dict:
    """Re-embed stale rows."""
    ...


urlpatterns = [..., *service.urls, *agent.urls]

A service says what exists; an agent says what can be done. Neither knows the other.

Development

uv sync
uv run pytest                                          # the contract and the service
uv run pytest tests/hook --ds=hook_project.settings    # the hook agent: a process that is no service
uv run basedpyright

Releases are cut from conventional commits on main (tag-only, like the other Arkitekt packages) and uploaded to PyPI.