Metadata-Version: 2.5
Name: arkitekt-service
Version: 1.6.0
Summary: What a service of an Arkitekt hub is made with: the contract its image answers the installer, its declaration to rekuest, and its hook agent
Author-email: jhnnsrs <jhnnsrs@gmail.com>
License: MIT
Requires-Python: <4,>=3.12
Requires-Dist: django>=5
Requires-Dist: httpx>=0.27
Requires-Dist: joserfc>=1.7
Requires-Dist: pydantic-settings>=2.3
Requires-Dist: pydantic>=2.7
Requires-Dist: pyyaml>=6
Provides-Extra: koherent
Requires-Dist: koherent>=4.1; extra == 'koherent'
Description-Content-Type: text/markdown

# arkitekt-service

What a service of an [Arkitekt](https://arkitekt.live) hub is made with. Three parts, for three
different things a service process does:

| | |
|---|---|
| `arkitekt_service.contract` | What the service's **image** answers the hub's installer: what it needs, its own config written from the hub's facts, its migrations and upgrades. |
| `arkitekt_service.service` | What the service **is** to the hub's rekuest: the structures it hosts and the signals it emits. |
| `arkitekt_service.hook` | What can be **done** in its process: a HookAgent, whose actions rekuest reaches over HTTP. |

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:

```
arkitekt-service describe    # what it needs from a hub and offers to it (JSON)
arkitekt-service render      # this release's config, from the hub's facts
arkitekt-service check       # does this release read a config as written?
arkitekt-service migrate     # its database migrations, as a step
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 container serves; a job prepares

A service's container does one thing: serve. Its start script starts the server and nothing
else. Everything its database needs first is `migrate`: wait for the database, apply the
release's migrations, then run the commands the service declared as its `setup` (an admin
account, seeded rows), all in one process. Whoever starts the service runs it as a job of its
own, once per build, before the first start and before an update's:

```
docker compose run --rm --no-deps mikro arkitekt-service migrate
```

or, in a compose file that has no installer, as a service the server waits for:

```yaml
mikro-migrate:
  image: jhnnsrs/mikro:7
  command: arkitekt-service migrate
mikro:
  image: jhnnsrs/mikro:7
  depends_on:
    mikro-migrate:
      condition: service_completed_successfully
```

A container that merely restarts then does none of it. No `run.sh` migrates, seeds or waits
for a database, and neither does a development one.

What `describe` prints also says how the image is run, so an installer assumes none of it:

- `identifier`: what the service is registered as, and what a client asks for.
- `jobs`: what can be run in the image beside its start, by name, each with the command that
  runs it. A service declares its own (`Job(("ensureadmin",), "Create the operator account")`
  on its contract); `migrate` is every service's, and lists the ones it runs as its setup
  (`includes`). An operator runs any of them again by name, e.g. `konstruktor job run mikro
  ensureadmin`, which is `arkitekt-service job ensureadmin` in a container of the image.
- `prepare`: which job brings the database to the release (`migrate`), or `null` for a
  service with nothing to prepare.
- `sidecars`: what the service does not run without and ships as an image of its own
  (rekuest's takt), named from the service's image.
- `serve` and `debug`: what a container of the image runs to serve, in production and in
  development (`bash run.sh`, `bash run-debug.sh` unless the service says otherwise). An
  installer writes the one that applies as the service's command.
- `render`: what writes the release's config from the hub's facts.

The image's own command is `describe`:

```dockerfile
CMD ["arkitekt-service", "describe"]
```

So an installer asks by running the image with no command, and assumes nothing of what is
inside: every other command it runs is one the answer named. A service written in another
language takes part by printing the same description as its own command. Whoever starts the
image by hand gets the description too, and beside it, on stderr, a note saying that nothing
is being served and what to run instead.

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

```python
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", identifier="live.arkitekt.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

```python
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.
