Enhance FastAPI app for Kubernetes resilience and pod host assignment issues

app/api/endpoints/health.py

@@ -1,15 +1,70 @@
-from fastapi import APIRouter, Depends
+from typing import Any, Dict
+
+from fastapi import APIRouter, Depends, Query
+from sqlalchemy.exc import SQLAlchemyError
 from sqlalchemy.orm import Session
 
+from app.core.orchestration import get_orchestration_status
 from app.db.session import get_db
 
 router = APIRouter()
 
 
 @router.get("")
-def health_check(db: Session = Depends(get_db)):
+def health_check(
+    db: Session = Depends(get_db),
+    detailed: bool = Query(False, description="Include detailed diagnostics information")
+) -> Dict[str, Any]:
     """
     Health check endpoint for the API
+    
+    This endpoint checks the health of various components of the application:
+    - Database connectivity
+    - Host and pod status
+    - Application readiness
+    
+    Args:
+        detailed: Whether to include detailed diagnostics information
+        
+    Returns:
+        Dict[str, Any]: Health status of the application
     """
-    # Simple health check that ensures the database connection is working
+    # Basic health response
-    return {"status": "healthy", "database": "connected"}
+    response = {
+        "status": "healthy"
+    }
+    
+    # Check database connectivity
+    try:
+        # Simple query to verify database connectivity
+        db.execute("SELECT 1")
+        database_status = "connected"
+        database_error = None
+    except SQLAlchemyError as e:
+        database_status = "error"
+        database_error = str(e)
+    except Exception as e:
+        database_status = "error"
+        database_error = str(e)
+    
+    response["database"] = {
+        "status": database_status
+    }
+    
+    # Add orchestration status if detailed information is requested
+    if detailed:
+        response["orchestration"] = get_orchestration_status()
+        
+        # Add more detailed database information if there was an error
+        if database_error:
+            response["database"]["error"] = database_error
+    elif database_status != "connected":
+        # Always include error information in the basic response
+        response["status"] = "unhealthy"
+        response["database"]["error"] = database_error
+    
+    # Set overall status based on component statuses
+    if database_status != "connected":
+        response["status"] = "unhealthy"
+        
+    return response

app/core/orchestration.py

@@ -0,0 +1,118 @@
+"""
+Utilities to handle container orchestration environments and improve
+resilience in Kubernetes-like environments.
+"""
+
+import logging
+import os
+import socket
+import time
+from typing import Dict, Optional, Tuple
+
+logger = logging.getLogger(__name__)
+
+# Maximum attempts to resolve host
+MAX_HOST_RESOLVE_ATTEMPTS = 5
+# Delay between attempts in seconds
+HOST_RESOLVE_DELAY = 2
+
+
+def get_host_info() -> Dict[str, str]:
+    """
+    Get information about the host where the application is running.
+    
+    This helps diagnose container and pod issues in orchestration environments.
+    
+    Returns:
+        Dict[str, str]: Dictionary with host information
+    """
+    info = {
+        "hostname": "unknown",
+        "ip_address": "unknown", 
+        "pod_name": os.environ.get("HOSTNAME", "unknown"),
+        "namespace": os.environ.get("POD_NAMESPACE", "unknown"),
+    }
+    
+    try:
+        info["hostname"] = socket.gethostname()
+        info["ip_address"] = socket.gethostbyname(info["hostname"])
+    except Exception as e:
+        logger.warning(f"Could not resolve host information: {str(e)}")
+    
+    return info
+
+
+def check_host_connectivity(timeout: int = 5) -> Tuple[bool, Optional[str]]:
+    """
+    Check if the host has network connectivity.
+    
+    Args:
+        timeout: Timeout in seconds
+        
+    Returns:
+        Tuple[bool, Optional[str]]: (Success, Error message if any)
+    """
+    try:
+        # Try to resolve a common external domain
+        socket.getaddrinfo("google.com", 80, proto=socket.IPPROTO_TCP)
+        return True, None
+    except socket.gaierror as e:
+        return False, f"DNS resolution error: {str(e)}"
+    except socket.timeout:
+        return False, "Connection timed out"
+    except Exception as e:
+        return False, f"Unknown connection error: {str(e)}"
+
+
+def wait_for_host_assignment(max_attempts: int = MAX_HOST_RESOLVE_ATTEMPTS,
+                            delay: int = HOST_RESOLVE_DELAY) -> Tuple[bool, Optional[str]]:
+    """
+    Wait for the host to be assigned in container orchestration environments.
+    
+    This helps to handle situations where the pod is scheduled but the host
+    assignment is delayed.
+    
+    Args:
+        max_attempts: Maximum number of attempts to resolve the host
+        delay: Delay between attempts in seconds
+        
+    Returns:
+        Tuple[bool, Optional[str]]: (Success, Error message if any)
+    """
+    attempt = 0
+    
+    while attempt < max_attempts:
+        try:
+            hostname = socket.gethostname()
+            ip_address = socket.gethostbyname(hostname)
+            logger.info(f"Host assigned: {hostname} ({ip_address})")
+            return True, None
+        except socket.gaierror as e:
+            logger.warning(f"Host not resolved yet (attempt {attempt+1}/{max_attempts}): {str(e)}")
+            attempt += 1
+            time.sleep(delay)
+    
+    return False, "Maximum attempts reached, host still not assigned"
+
+
+def get_orchestration_status() -> Dict[str, any]:
+    """
+    Get comprehensive status information about the container orchestration environment.
+    
+    Returns:
+        Dict: Orchestration status information
+    """
+    host_info = get_host_info()
+    connectivity_status, connectivity_error = check_host_connectivity()
+    startup_error = os.environ.get("APP_STARTUP_ERROR", None)
+    
+    return {
+        "host": host_info,
+        "ready": os.environ.get("APP_READY", "false") == "true",
+        "connectivity": {
+            "status": "connected" if connectivity_status else "disconnected",
+            "error": connectivity_error
+        },
+        "startup_error": startup_error,
+        "environment": "kubernetes" if "KUBERNETES_SERVICE_HOST" in os.environ else "unknown"
+    }

main.py

@@ -1,3 +1,9 @@
+import logging
+import os
+import socket
+import sys
+from contextlib import asynccontextmanager
+
 import uvicorn
 from fastapi import FastAPI
 from starlette.middleware.cors import CORSMiddleware
@@ -5,13 +11,75 @@ from starlette.middleware.cors import CORSMiddleware
 from app.api.api import api_router
 from app.core.config import settings
 
+# Configure logging
+logging.basicConfig(
+    level=logging.INFO,
+    format="%(asctime)s - %(name)s - %(levelname)s - %(message)s",
+    handlers=[logging.StreamHandler(sys.stdout)]
+)
+logger = logging.getLogger(__name__)
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """
+    Lifespan events for the FastAPI application
+    Handles startup and shutdown gracefully
+    """
+    # Startup: Check for host availability and other system requirements
+    try:
+        hostname = socket.gethostname()
+        ip_address = socket.gethostbyname(hostname)
+        logger.info(f"Starting application on host: {hostname}, IP: {ip_address}")
+        
+        # Check required directories exist
+        from pathlib import Path
+        db_dir = Path("/app") / "storage" / "db"
+        db_dir.mkdir(parents=True, exist_ok=True)
+        logger.info(f"Database directory confirmed at: {db_dir}")
+        
+        # Set environment variable to indicate we're ready
+        os.environ["APP_READY"] = "true"
+        logger.info("Application startup completed successfully")
+    except Exception as e:
+        logger.error(f"Application startup error: {str(e)}")
+        # Critical errors during startup should be propagated, but still allow the app to run
+        os.environ["APP_READY"] = "false"
+        os.environ["APP_STARTUP_ERROR"] = str(e)
+    
+    yield  # This is where the app runs
+    
+    # Shutdown: Perform cleanup operations
+    try:
+        logger.info("Application shutting down gracefully")
+        # Any cleanup operations would go here
+    except Exception as e:
+        logger.error(f"Error during application shutdown: {str(e)}")
+
+
 app = FastAPI(
     title=settings.PROJECT_NAME,
     openapi_url=f"{settings.API_V1_STR}/openapi.json",
     description="Generic REST API Service with FastAPI and SQLite",
     version="0.1.0",
+    lifespan=lifespan,
 )
 
+# Add middleware for exception handling
+@app.middleware("http")
+async def add_process_time_header(request, call_next):
+    try:
+        response = await call_next(request)
+        return response
+    except Exception as e:
+        logger.error(f"Request error: {str(e)}")
+        # Return error to the client
+        from fastapi.responses import JSONResponse
+        return JSONResponse(
+            status_code=500,
+            content={"detail": "Internal server error", "type": "server_error"}
+        )
+
 # Set all CORS enabled origins
 if settings.BACKEND_CORS_ORIGINS:
     app.add_middleware(