Internal: executor selection policy system

Problem: for testing, we wish to switch between different ways of
selecting executors (ex: repeat tests on a specific list of CRNs, use
local executors for integration tests).

Solution: introduce the `ExecutorSelectionPolicy` class. Using this
class, the caller can parameterize the way executors are selected,
blacklisted, etc.

src/aleph_vrf/coordinator/executor_selection.py

@@ -0,0 +1,89 @@
+import abc
+import json
+from pathlib import Path
+from typing import List, Dict, Any, AsyncIterator
+import random
+
+import aiohttp
+from aleph_message.models import ItemHash
+
+from aleph_vrf.models import Executor, Node, AlephExecutor, ComputeResourceNode
+from aleph_vrf.settings import settings
+
+
+class ExecutorSelectionPolicy(abc.ABC):
+    @abc.abstractmethod
+    async def select_executors(self, nb_executors: int) -> List[Executor]:
+        ...
+
+
+async def _get_corechannel_aggregate() -> Dict[str, Any]:
+    async with aiohttp.ClientSession(settings.API_HOST) as session:
+        url = (
+            f"/api/v0/aggregates/{settings.CORECHANNEL_AGGREGATE_ADDRESS}.json?"
+            f"keys={settings.CORECHANNEL_AGGREGATE_KEY}"
+        )
+        async with session.get(url) as response:
+            if response.status != 200:
+                raise ValueError(f"CRN list not available")
+
+            return await response.json()
+
+
+class ExecuteOnAleph(ExecutorSelectionPolicy):
+    def __init__(self, vm_function: ItemHash):
+        self.vm_function = vm_function
+
+    @staticmethod
+    async def _list_compute_nodes() -> AsyncIterator[ComputeResourceNode]:
+        content = await _get_corechannel_aggregate()
+
+        if (
+            not content["data"]["corechannel"]
+            or not content["data"]["corechannel"]["resource_nodes"]
+        ):
+            raise ValueError(f"Bad CRN list format")
+
+        resource_nodes = content["data"]["corechannel"]["resource_nodes"]
+
+        for resource_node in resource_nodes:
+            # Filter nodes by score, with linked status
+            if resource_node["status"] == "linked" and resource_node["score"] > 0.9:
+                node_address = resource_node["address"].strip("/")
+                node = ComputeResourceNode(
+                    hash=resource_node["hash"],
+                    address=node_address,
+                    score=resource_node["score"],
+                )
+                yield node
+
+    @staticmethod
+    def _get_unauthorized_nodes() -> List[str]:
+        unauthorized_nodes_list_path = Path(__file__).with_name(
+            "unauthorized_node_list.json"
+        )
+        if unauthorized_nodes_list_path.is_file():
+            with open(unauthorized_nodes_list_path, "rb") as fd:
+                return json.load(fd)
+
+        return []
+
+    async def select_executors(self, nb_executors: int) -> List[Executor]:
+        compute_nodes = self._list_compute_nodes()
+        blacklisted_nodes = self._get_unauthorized_nodes()
+        whitelisted_nodes = (
+            node
+            async for node in compute_nodes
+            if node.address not in blacklisted_nodes
+        )
+        executors = [
+            AlephExecutor(node=node, vm_function=self.vm_function)
+            async for node in whitelisted_nodes
+        ]
+
+        if len(executors) < nb_executors:
+            raise ValueError(
+                f"Not enough CRNs linked, only {len(executors)} "
+                f"available from {nb_executors} requested"
+            )
+        return random.sample(executors, nb_executors)

src/aleph_vrf/coordinator/vrf.py

@@ -4,7 +4,7 @@
 import random
 from hashlib import sha3_256
 from pathlib import Path
-from typing import Any, Dict, List, Type, TypeVar, Union
+from typing import Dict, List, Type, TypeVar, Union
 from uuid import uuid4
 
 import aiohttp
@@ -15,9 +15,9 @@
 from pydantic import BaseModel
 from pydantic.json import pydantic_encoder
 
+from aleph_vrf.coordinator.executor_selection import ExecuteOnAleph
 from aleph_vrf.models import (
     CRNVRFResponse,
-    Node,
     VRFRequest,
     VRFResponse,
     PublishedVRFResponseHash,
@@ -59,73 +59,12 @@ async def post_node_vrf(url: str, model: Type[M]) -> M:
             return model.parse_obj(response["data"])
 
 
-async def _get_corechannel_aggregate() -> Dict[str, Any]:
-    async with aiohttp.ClientSession(settings.API_HOST) as session:
-        url = (
-            f"/api/v0/aggregates/{settings.CORECHANNEL_AGGREGATE_ADDRESS}.json?"
-            f"keys={settings.CORECHANNEL_AGGREGATE_KEY}"
-        )
-        async with session.get(url) as response:
-            if response.status != 200:
-                raise ValueError(f"CRN list not available")
-
-            return await response.json()
-
-
-def _get_unauthorized_node_list() -> List[str]:
-    unauthorized_nodes_list_path = Path(__file__).with_name(
-        "unauthorized_node_list.json"
-    )
-    if unauthorized_nodes_list_path.is_file():
-        with open(unauthorized_nodes_list_path, "rb") as fd:
-            return json.load(fd)
-
-    return []
-
-
-async def select_random_executors(
-    node_amount: int, unauthorized_nodes: List[str]
-) -> List[Executor]:
-    node_list: List[Executor] = []
-
-    content = await _get_corechannel_aggregate()
-
-    if (
-        not content["data"]["corechannel"]
-        or not content["data"]["corechannel"]["resource_nodes"]
-    ):
-        raise ValueError(f"Bad CRN list format")
-
-    resource_nodes = content["data"]["corechannel"]["resource_nodes"]
-
-    for resource_node in resource_nodes:
-        # Filter nodes by score, with linked status and remove unauthorized nodes
-        if (
-            resource_node["status"] == "linked"
-            and resource_node["score"] > 0.9
-            and resource_node["address"].strip("/") not in unauthorized_nodes
-        ):
-            node_address = resource_node["address"].strip("/")
-            node = ComputeResourceNode(
-                hash=resource_node["hash"],
-                address=node_address,
-                score=resource_node["score"],
-            )
-            node_list.append(AlephExecutor(node=node, vm_function=settings.FUNCTION))
-
-    if len(node_list) < node_amount:
-        raise ValueError(
-            f"Not enough CRNs linked, only {len(node_list)} available from {node_amount} requested"
-        )
-
-    # Randomize node order
-    return random.sample(node_list, min(node_amount, len(node_list)))
-
-
 async def generate_vrf(account: ETHAccount) -> VRFResponse:
     nb_executors = settings.NB_EXECUTORS
-    unauthorized_nodes = _get_unauthorized_node_list()
-    executors = await select_random_executors(nb_executors, unauthorized_nodes)
+    vm_function = settings.FUNCTION
+
+    executor_selection_policy = ExecuteOnAleph(vm_function=vm_function)
+    executors = await executor_selection_policy.select_executors(nb_executors)
     selected_nodes_json = json.dumps(
         [executor.node for executor in executors], default=pydantic_encoder
     ).encode(encoding="utf-8")

tests/coordinator/test_vrf.py → tests/coordinator/test_executor_selection.py

@@ -1,8 +1,9 @@
 from typing import Any, Dict
 
 import pytest
+from aleph_message.models import ItemHash
 
-from aleph_vrf.coordinator.vrf import select_random_executors
+from aleph_vrf.coordinator.executor_selection import ExecuteOnAleph
 
 
 @pytest.fixture
@@ -136,21 +137,21 @@ def fixture_nodes_aggregate() -> Dict[str, Any]:
 @pytest.mark.asyncio
 async def test_select_random_nodes(fixture_nodes_aggregate: Dict[str, Any], mocker):
     network_fixture = mocker.patch(
-        "aleph_vrf.coordinator.vrf._get_corechannel_aggregate",
+        "aleph_vrf.coordinator.executor_selection._get_corechannel_aggregate",
         return_value=fixture_nodes_aggregate,
     )
+    executor_selection_policy = ExecuteOnAleph(vm_function=ItemHash("cafe" * 16))
 
-    executors = await select_random_executors(3, [])
+    executors = await executor_selection_policy.select_executors(3)
     # Sanity check, avoid network accesses
     network_fixture.assert_called_once()
 
     assert len(executors) == 3
 
+    resource_nodes = fixture_nodes_aggregate["data"]["corechannel"]["resource_nodes"]
     with pytest.raises(ValueError) as exception:
-        resource_nodes = fixture_nodes_aggregate["data"]["corechannel"][
-            "resource_nodes"
-        ]
-        await select_random_executors(len(resource_nodes), [])
+        await executor_selection_policy.select_executors(len(resource_nodes))
+
     assert (
         str(exception.value)
         == f"Not enough CRNs linked, only 4 available from 5 requested"
@@ -162,24 +163,33 @@ async def test_select_random_nodes_with_unauthorized(
     fixture_nodes_aggregate: Dict[str, Any], mocker
 ):
     network_fixture = mocker.patch(
-        "aleph_vrf.coordinator.vrf._get_corechannel_aggregate",
+        "aleph_vrf.coordinator.executor_selection._get_corechannel_aggregate",
         return_value=fixture_nodes_aggregate,
     )
+    blacklist = ["https://aleph2.serverrg.eu"]
+    executor_selection_policy = ExecuteOnAleph(vm_function=ItemHash("cafe" * 16))
+    with mocker.patch.object(
+        executor_selection_policy, "_get_unauthorized_nodes", return_value=blacklist
+    ):
+        executors = await executor_selection_policy.select_executors(3)
+        # Sanity check, avoid network accesses
+        network_fixture.assert_called_once()
 
-    # Sanity check, avoid network accesses
-    assert network_fixture.called_once
+        assert len(executors) == 3
 
-    executors = await select_random_executors(3, ["https://aleph2.serverrg.eu"])
-    assert len(executors) == 3
+        for blacklisted_node_address in blacklist:
+            assert blacklisted_node_address not in [
+                executor.node.address for executor in executors
+            ]
 
-    with pytest.raises(ValueError) as exception:
-        resource_nodes = fixture_nodes_aggregate["data"]["corechannel"][
-            "resource_nodes"
-        ]
-        _ = await select_random_executors(
-            len(resource_nodes) - 1, ["https://aleph2.serverrg.eu"]
+        with pytest.raises(ValueError) as exception:
+            resource_nodes = fixture_nodes_aggregate["data"]["corechannel"][
+                "resource_nodes"
+            ]
+            _ = await executor_selection_policy.select_executors(
+                len(resource_nodes) - 1
+            )
+        assert (
+            str(exception.value)
+            == f"Not enough CRNs linked, only 3 available from 4 requested"
         )
-    assert (
-        str(exception.value)
-        == f"Not enough CRNs linked, only 3 available from 4 requested"
-    )