feat: IPv6 dual-stack support for server bind addresses (#863)

Change default bind address from 0.0.0.0/127.0.0.1 to :: (dual-stack)
across all server components, enabling deployment on IPv6-only Kubernetes
clusters (e.g. EKS in hybrid VPC where pods have only IPv6 addresses).

Binding to :: on Linux accepts both IPv4 and IPv6 connections by default,
so existing IPv4-only deployments continue to work without changes.

Closes #863

Made-with: Cursor

Author: soheilkhan

charts/mcpgw/templates/deployment.yaml

@@ -50,7 +50,7 @@ spec:
             {{- end }}
           env:
             - name: HOST
-              value: 0.0.0.0
+              value: "::"
             {{- if .Values.app.embeddingsApiKeyExistingSecret }}
             - name: EMBEDDINGS_API_KEY
               valueFrom:

docker/auth-entrypoint.sh

@@ -75,7 +75,9 @@ while True:
     echo "MongoDB is ready."
 fi
 
-echo "Starting Auth Server..."
+BIND_HOST="${BIND_HOST:-::}"
+
+echo "Starting Auth Server (host=$BIND_HOST)..."
 cd /app
 source .venv/bin/activate
-exec uvicorn server:app --host 0.0.0.0 --port 8888 --proxy-headers --forwarded-allow-ips='*'
+exec uvicorn server:app --host "$BIND_HOST" --port 8888 --proxy-headers --forwarded-allow-ips='*'

docker/registry-entrypoint.sh

@@ -255,11 +255,14 @@ export EMBEDDINGS_PROVIDER=$EMBEDDINGS_PROVIDER
 export EMBEDDINGS_MODEL_NAME=$EMBEDDINGS_MODEL_NAME
 export EMBEDDINGS_MODEL_DIMENSIONS=$EMBEDDINGS_MODEL_DIMENSIONS
 
+BIND_HOST="${BIND_HOST:-::}"
+
 echo "Starting MCP Registry in the background..."
 cd /app
 source /app/.venv/bin/activate
-uvicorn registry.main:app --host 0.0.0.0 --port 7860 --proxy-headers --forwarded-allow-ips='*' &
-echo "MCP Registry started."
+uvicorn registry.main:app --host "$BIND_HOST" --port 7860 --proxy-headers --forwarded-allow-ips='*' &
+UVICORN_PID=$!
+echo "MCP Registry started (PID=$UVICORN_PID, host=$BIND_HOST)."
 
 # Wait for nginx config to be generated (check that placeholders are replaced)
 echo "Waiting for nginx configuration to be generated..."

registry/core/config.py

@@ -33,6 +33,9 @@ class Settings(BaseSettings):
         extra="ignore",  # Ignore extra environment variables
     )
 
+    # Network binding: "::" for dual-stack IPv4+IPv6, "0.0.0.0" for IPv4 only
+    bind_host: str = "::"
+
     # Auth settings
     secret_key: str = ""
     session_cookie_name: str = "mcp_gateway_session"

registry/main.py

@@ -1067,7 +1067,7 @@ async def serve_react_app(full_path: str):
 
     uvicorn.run(
         "registry.main:app",
-        host=os.getenv("REGISTRY_HOST", "127.0.0.1"),  # nosec B104
+        host=settings.bind_host,  # nosec B104 - dual-stack IPv4+IPv6 by default
         port=7860,
         reload=True,
         log_level="info",

servers/currenttime/server.py

@@ -137,9 +137,8 @@ def get_config() -> str:
 
 
 def main():
-    # Use configurable host with secure default (127.0.0.1)
-    # Set HOST=0.0.0.0 in environment for Docker deployments
-    host = os.environ.get("HOST", "127.0.0.1")
+    # Use configurable host - "::" enables dual-stack IPv4+IPv6
+    host = os.environ.get("HOST", "::")
 
     # Log startup information
     logger.info(f"Starting CurrentTime server on {host}:{args.port}")