Split toolhive_host into separate variables for API and workload communication

.github/workflows/integration-tests.yml

@@ -59,6 +59,7 @@ jobs:
           --transport streamable-http
           --proxy-port 8080
           --env TOOLHIVE_HOST=172.17.0.1
+          --env WORKLOAD_HOST=172.17.0.1
           --env TOOLHIVE_PORT=9090
           --env WORKLOAD_POLLING_INTERVAL=2
           --env ALLOWED_GROUPS=default

Dockerfile

@@ -106,6 +106,7 @@ USER app
 
 # Set default environment variables for container deployment
 ENV TOOLHIVE_HOST=host.docker.internal
+ENV WORKLOAD_HOST=host.docker.internal
 ENV FASTEMBED_CACHE_PATH=/app/.cache/fastembed
 ENV TIKTOKEN_CACHE_DIR=/app/.cache/tiktoken
 ENV COLORED_LOGS=false

Taskfile.yml

@@ -102,6 +102,7 @@ tasks:
     desc: Run the application locally
     env:
       TOOLHIVE_HOST: "localhost"
+      WORKLOAD_HOST: "localhost"
       TOOLHIVE_PORT: "8080"
     cmds:
       - uv run mtm

src/mcp_optimizer/cli.py

@@ -198,6 +198,7 @@ def main(**kwargs: Any) -> None:
 
     toolhive_client = ToolhiveClient(
         host=config.toolhive_host,
+        workload_host=config.workload_host,
         port=config.toolhive_port,
         scan_port_start=config.toolhive_start_port_scan,
         scan_port_end=config.toolhive_end_port_scan,

src/mcp_optimizer/config.py

@@ -59,6 +59,9 @@ def normalize_runtime_mode(cls, v) -> str:
     toolhive_host: str = Field(
         default="localhost", min_length=1, description="Host for ToolHive API"
     )
+    workload_host: str = Field(
+        default="localhost", min_length=1, description="Host for MCP workload connections"
+    )
     toolhive_port: int | None = Field(
         default=None, ge=1024, le=65535, description="Port for ToolHive API (1024-65535)"
     )
@@ -475,6 +478,7 @@ def _populate_config_from_env() -> dict[str, Any]:
         "MCP_PORT": "mcp_port",
         "RELOAD_SERVER": "reload_server",
         "TOOLHIVE_HOST": "toolhive_host",
+        "WORKLOAD_HOST": "workload_host",
         "TOOLHIVE_PORT": "toolhive_port",
         "TOOLHIVE_START_PORT_SCAN": "toolhive_start_port_scan",
         "TOOLHIVE_END_PORT_SCAN": "toolhive_end_port_scan",

src/mcp_optimizer/server.py

@@ -154,6 +154,7 @@ def initialize_server_components(config: MCPOptimizerConfig) -> None:
     mcp.settings.port = config.mcp_port
     toolhive_client = ToolhiveClient(
         host=config.toolhive_host,
+        workload_host=config.workload_host,
         port=config.toolhive_port,
         scan_port_start=config.toolhive_start_port_scan,
         scan_port_end=config.toolhive_end_port_scan,

src/mcp_optimizer/toolhive/toolhive_client.py

@@ -5,7 +5,7 @@
 import asyncio
 from functools import wraps
 from typing import Any, Awaitable, Callable, Self, TypeVar
-from urllib.parse import urlparse
+from urllib.parse import urlparse, urlunparse
 
 import httpx
 import structlog
@@ -43,6 +43,7 @@ class ToolhiveClient:
     def __init__(
         self,
         host: str,
+        workload_host: str,
         port: int | None,
         scan_port_start: int,
         scan_port_end: int,
@@ -57,6 +58,7 @@ def __init__(
 
         Args:
             host: Toolhive server host
+            workload_host: Host for MCP workload connections
             port: Toolhive server port
             scan_port_start: Start of port range to scan for Toolhive
             scan_port_end: End of port range to scan for Toolhive
@@ -68,6 +70,7 @@ def __init__(
                 (useful when ToolHive is not needed, e.g., K8s mode)
         """
         self.thv_host = host
+        self.workload_host = workload_host
         self.timeout = timeout
         self.max_retries = max_retries
         self.initial_backoff = initial_backoff
@@ -379,6 +382,35 @@ def client(self) -> httpx.AsyncClient:
             self._client = httpx.AsyncClient(timeout=self.timeout)
         return self._client
 
+    def replace_localhost_in_url(self, url: str | None) -> str | None:
+        """
+        Replace localhost/127.0.0.1 with the workload host in a URL.
+
+        This is required since in docker/podman containers, we cannot use
+        localhost/127.0.0.1 to reach services on the host machine.
+
+        Args:
+            url: The URL to process (can be None)
+
+        Returns:
+            The URL with localhost/127.0.0.1 replaced by workload_host,
+            or None if input was None
+        """
+        if not url:
+            return url
+
+        parsed_url = urlparse(url)
+        hostname = parsed_url.hostname
+
+        if hostname and hostname in ("localhost", "127.0.0.1"):
+            # Replace hostname only in netloc, not in path/query/fragment
+            new_netloc = parsed_url.netloc.replace(hostname, self.workload_host, 1)
+            parsed = parsed_url._replace(netloc=new_netloc)
+            # urlunparse returns str when input is from urlparse(str)
+            return str(urlunparse(parsed))
+
+        return url
+
     async def list_workloads(self, all_workloads: bool = False) -> WorkloadListResponse:
         """
         Get a list of workloads from Toolhive.
@@ -410,15 +442,11 @@ async def _list_workloads_impl() -> WorkloadListResponse:
                 logger.warning("No workloads found", all_workloads=all_workloads)
                 return WorkloadListResponse(workloads=[])
 
-            # Replace the localhost/127.0.0.1 host with the toolhive host
+            # Replace the localhost/127.0.0.1 host with the workload host
             # This is required since in docker/podman container, we cannot use
             # localhost/127.0.0.1
             for workload in workload_list.workloads:
-                if workload.url:
-                    parsed_url = urlparse(workload.url)
-                    workload_host = parsed_url.hostname
-                    if workload_host in ("localhost", "127.0.0.1"):
-                        workload.url = workload.url.replace(workload_host, self.thv_host)
+                workload.url = self.replace_localhost_in_url(workload.url)
 
             logger.info(
                 "Successfully fetched workloads",
@@ -458,12 +486,8 @@ async def _get_workload_details_impl() -> Workload:
             data = response.json()
             workload = Workload.model_validate(data)
 
-            # Replace localhost/127.0.0.1 with the toolhive host (same as list_workloads)
-            if workload.url:
-                parsed_url = urlparse(workload.url)
-                workload_host = parsed_url.hostname
-                if workload_host in ("localhost", "127.0.0.1"):
-                    workload.url = workload.url.replace(workload_host, self.thv_host)
+            # Replace localhost/127.0.0.1 with the workload host (same as list_workloads)
+            workload.url = self.replace_localhost_in_url(workload.url)
 
             logger.info(
                 "Successfully fetched workload details",

tests/test_polling_manager.py

@@ -56,6 +56,7 @@ async def mock_is_toolhive_available(self, host, port):
 
     return ToolhiveClient(
         host="localhost",
+        workload_host="localhost",
         port=8080,
         scan_port_start=50000,
         scan_port_end=50100,