Add REST plugin for user-defined policies

docs/docs/guides/plugins.md

@@ -113,4 +113,14 @@ class ExamplePolicy(ApplyPolicy):
 
 </div>
 
-For more information on the plugin development, see the [plugin example](https://github.com/dstackai/dstack/tree/master/examples/plugins/example_plugin).
+## Built-in Plugins
+
+### REST Plugin
+`rest_plugin` is a builtin `dstack` plugin that allows writing your custom plugins as API servers, so you don't need to install plugins as Python packages.
+
+Plugins implemented as API servers have advantages over plugins implemented as Python packages in some cases:
+* No dependency conflicts with `dstack`.
+* You can use any programming language.
+* If you run the `dstack` server via Docker, you don't need to extend the `dstack` server image with plugins or map them via volumes.
+
+To get started, check out the [plugin server example](/examples/plugins/example_plugin_server/README.md).

examples/plugins/example_plugin_server/.python-version

@@ -0,0 +1 @@
+3.11

examples/plugins/example_plugin_server/README.md

@@ -0,0 +1,30 @@
+## Overview
+
+If you wish to hook up your own plugin server through `dstack` builtin `rest_plugin`, here's a basic example on how to do so.
+
+## Steps
+
+
+1. Install required dependencies for the plugin server:
+
+    ```bash
+    uv sync 
+    ```
+
+1. Start the plugin server locally:
+
+    ```bash
+    fastapi dev app/main.py 
+    ```
+
+1. Enable `rest_plugin` in `server/config.yaml`:
+
+    ```yaml
+   plugins:
+    - rest_plugin
+    ```
+
+1. Point the `dstack` server to your plugin server:
+    ```bash
+    export DSTACK_PLUGIN_SERVICE_URI=http://127.0.0.1:8000
+    ```

examples/plugins/example_plugin_server/app/main.py

@@ -0,0 +1,56 @@
+import logging
+
+from fastapi import FastAPI
+
+from app.utils import configure_logging
+from dstack.plugins.builtin.rest_plugin import (
+    FleetSpecRequest,
+    FleetSpecResponse,
+    GatewaySpecRequest,
+    GatewaySpecResponse,
+    RunSpecRequest,
+    RunSpecResponse,
+    VolumeSpecRequest,
+    VolumeSpecResponse,
+)
+
+configure_logging()
+logger = logging.getLogger(__name__)
+
+app = FastAPI()
+
+
+@app.post("/apply_policies/on_run_apply")
+async def on_run_apply(request: RunSpecRequest) -> RunSpecResponse:
+    logger.info(
+        f"Received run spec request from user {request.user} and project {request.project}"
+    )
+    response = RunSpecResponse(spec=request.spec, error=None)
+    return response
+
+
+@app.post("/apply_policies/on_fleet_apply")
+async def on_fleet_apply(request: FleetSpecRequest) -> FleetSpecResponse:
+    logger.info(
+        f"Received fleet spec request from user {request.user} and project {request.project}"
+    )
+    response = FleetSpecResponse(request.spec, error=None)
+    return response
+
+
+@app.post("/apply_policies/on_volume_apply")
+async def on_volume_apply(request: VolumeSpecRequest) -> VolumeSpecResponse:
+    logger.info(
+        f"Received volume spec request from user {request.user} and project {request.project}"
+    )
+    response = VolumeSpecResponse(request.spec, error=None)
+    return response
+
+
+@app.post("/apply_policies/on_gateway_apply")
+async def on_gateway_apply(request: GatewaySpecRequest) -> GatewaySpecResponse:
+    logger.info(
+        f"Received gateway spec request from user {request.user} and project {request.project}"
+    )
+    response = GatewaySpecResponse(request.spec, error=None)
+    return response

examples/plugins/example_plugin_server/app/utils.py

@@ -0,0 +1,7 @@
+import logging
+import os
+
+
+def configure_logging():
+    log_level = os.getenv("LOG_LEVEL", "INFO").upper()
+    logging.basicConfig(level=log_level)

examples/plugins/example_plugin_server/pyproject.toml

@@ -0,0 +1,10 @@
+[project]
+name = "dstack-plugin-server"
+version = "0.1.0"
+description = "Example plugin server"
+readme = "README.md"
+requires-python = ">=3.11"
+dependencies = [
+    "fastapi[standard]>=0.115.12",
+    "dstack>=0.19.8"
+]

src/dstack/_internal/server/services/plugins.py

@@ -1,5 +1,6 @@
 import itertools
 from importlib import import_module
+from typing import Dict
 
 from backports.entry_points_selectable import entry_points  # backport for Python 3.9
 
@@ -12,50 +13,80 @@
 
 _PLUGINS: list[Plugin] = []
 
+_BUILTIN_PLUGINS: Dict[str, str] = {"rest_plugin": "dstack.plugins.builtin.rest_plugin:RESTPlugin"}
 
-def load_plugins(enabled_plugins: list[str]):
-    _PLUGINS.clear()
-    plugins_entrypoints = entry_points(group="dstack.plugins")
-    plugins_to_load = enabled_plugins.copy()
-    for entrypoint in plugins_entrypoints:
-        if entrypoint.name not in enabled_plugins:
-            logger.info(
-                ("Found not enabled plugin %s. Plugin will not be loaded."),
-                entrypoint.name,
-            )
-            continue
+
+class PluginEntrypoint:
+    def __init__(self, name: str, import_path: str, is_builtin: bool = False):
+        self.name = name
+        self.import_path = import_path
+        self.is_builtin = is_builtin
+
+    def load(self):
+        module_path, _, class_name = self.import_path.partition(":")
         try:
-            module_path, _, class_name = entrypoint.value.partition(":")
             module = import_module(module_path)
+            plugin_class = getattr(module, class_name, None)
+            if plugin_class is None:
+                logger.warning(
+                    ("Failed to load plugin %s: plugin class %s not found in module %s."),
+                    self.name,
+                    class_name,
+                    module_path,
+                )
+                return None
+            if not issubclass(plugin_class, Plugin):
+                logger.warning(
+                    ("Failed to load plugin %s: plugin class %s is not a subclass of Plugin."),
+                    self.name,
+                    class_name,
+                )
+                return None
+            return plugin_class()
         except ImportError:
             logger.warning(
                 (
                     "Failed to load plugin %s when importing %s."
                     " Ensure the module is on the import path."
                 ),
-                entrypoint.name,
-                entrypoint.value,
+                self.name,
+                self.import_path,
             )
-            continue
-        plugin_class = getattr(module, class_name, None)
-        if plugin_class is None:
-            logger.warning(
-                ("Failed to load plugin %s: plugin class %s not found in module %s."),
+            return None
+
+
+def load_plugins(enabled_plugins: list[str]):
+    _PLUGINS.clear()
+    entrypoints: dict[str, PluginEntrypoint] = {}
+    plugins_to_load = enabled_plugins.copy()
+    for entrypoint in entry_points(group="dstack.plugins"):
+        if entrypoint.name not in enabled_plugins:
+            logger.info(
+                ("Found not enabled plugin %s. Plugin will not be loaded."),
                 entrypoint.name,
-                class_name,
-                module_path,
             )
             continue
-        if not issubclass(plugin_class, Plugin):
-            logger.warning(
-                ("Failed to load plugin %s: plugin class %s is not a subclass of Plugin."),
-                entrypoint.name,
-                class_name,
+        else:
+            entrypoints[entrypoint.name] = PluginEntrypoint(
+                entrypoint.name, entrypoint.value, is_builtin=False
             )
-            continue
-        plugins_to_load.remove(entrypoint.name)
-        _PLUGINS.append(plugin_class())
-        logger.info("Loaded plugin %s", entrypoint.name)
+
+    for name, import_path in _BUILTIN_PLUGINS.items():
+        if name not in enabled_plugins:
+            logger.info(
+                ("Found not enabled builtin plugin %s. Plugin will not be loaded."),
+                name,
+            )
+        else:
+            entrypoints[name] = PluginEntrypoint(name, import_path, is_builtin=True)
+
+    for plugin_name, plugin_entrypoint in entrypoints.items():
+        plugin_instance = plugin_entrypoint.load()
+        if plugin_instance is not None:
+            _PLUGINS.append(plugin_instance)
+            plugins_to_load.remove(plugin_name)
+            logger.info("Loaded plugin %s", plugin_name)
+
     if plugins_to_load:
         logger.warning("Enabled plugins not found: %s", plugins_to_load)
 

src/dstack/plugins/builtin/rest_plugin/__init__.py

@@ -0,0 +1,18 @@
+# ruff: noqa: F401
+from dstack.plugins.builtin.rest_plugin._models import (
+    FleetSpecRequest,
+    FleetSpecResponse,
+    GatewaySpecRequest,
+    GatewaySpecResponse,
+    RunSpecRequest,
+    RunSpecResponse,
+    SpecApplyRequest,
+    SpecApplyResponse,
+    VolumeSpecRequest,
+    VolumeSpecResponse,
+)
+from dstack.plugins.builtin.rest_plugin._plugin import (
+    PLUGIN_SERVICE_URI_ENV_VAR_NAME,
+    CustomApplyPolicy,
+    RESTPlugin,
+)

src/dstack/plugins/builtin/rest_plugin/_models.py

@@ -0,0 +1,40 @@
+from typing import Generic, TypeVar
+
+from pydantic import BaseModel
+
+from dstack._internal.core.models.fleets import FleetSpec
+from dstack._internal.core.models.gateways import GatewaySpec
+from dstack._internal.core.models.runs import RunSpec
+from dstack._internal.core.models.volumes import VolumeSpec
+
+SpecType = TypeVar("SpecType", RunSpec, FleetSpec, VolumeSpec, GatewaySpec)
+
+
+class SpecApplyRequest(BaseModel, Generic[SpecType]):
+    user: str
+    project: str
+    spec: SpecType
+
+    # Override dict() to remove __orig_class__ attribute and avoid "TypeError: Object of type _GenericAlias is not JSON serializable"
+    # error. This issue doesn't happen though when running the code in pytest, only when running the server.
+    def dict(self, *args, **kwargs):
+        d = super().dict(*args, **kwargs)
+        d.pop("__orig_class__", None)
+        return d
+
+
+RunSpecRequest = SpecApplyRequest[RunSpec]
+FleetSpecRequest = SpecApplyRequest[FleetSpec]
+VolumeSpecRequest = SpecApplyRequest[VolumeSpec]
+GatewaySpecRequest = SpecApplyRequest[GatewaySpec]
+
+
+class SpecApplyResponse(BaseModel, Generic[SpecType]):
+    spec: SpecType
+    error: str | None = None
+
+
+RunSpecResponse = SpecApplyResponse[RunSpec]
+FleetSpecResponse = SpecApplyResponse[FleetSpec]
+VolumeSpecResponse = SpecApplyResponse[VolumeSpec]
+GatewaySpecResponse = SpecApplyResponse[GatewaySpec]