How to Troubleshoot Connection Issues with the Hindsight Server

To troubleshoot Hindsight server connection issues, verify the server process started successfully by checking for the "Hindsight server started" log message, test the /health endpoint for database connectivity, and validate your HINDSIGHT_API_DATABASE_URL and port configuration.

Connection problems with the Hindsight server from vectorize-io/hindsight typically originate from startup failures, port binding conflicts, or PostgreSQL connectivity issues. The server runs as a FastAPI-based HTTP API in a background thread managed by the Server class in hindsight-all/hindsight/server.py. Understanding how to interpret health checks and environment configuration will help you rapidly pinpoint whether the issue lies in server initialization, database access, or reverse-proxy routing.

Verifying Server Startup and Port Binding

The first step to troubleshoot connection issues is confirming that the Server class successfully initialized its background thread and bound to a network interface.

Connection Refused or Timeout Errors

If you receive a connection refused error, the server process likely never started or crashed during initialization. In hindsight-all/hindsight/server.py, the Server.start() method blocks until the server is reachable, then logs a success message:

logger.info(f"Hindsight server started at {self.url}")

This line appears at lines 80-83 in the source code. If you do not see this message in your logs, Server.start() may have raised a RuntimeError indicating the server failed to start within the timeout period.

Port Availability and Auto-Selection

Port conflicts occur when another process already occupies the configured port. The server handles port selection in hindsight-all/hindsight/server.py at lines 62-64:

self.port = port or _find_free_port()

When you initialize Server() without specifying a port (or pass port=None), the _find_free_port() helper automatically selects an available ephemeral port. To verify which port was selected, inspect the server.port attribute immediately after calling server.start():

from hindsight import Server

server = Server()  # Auto-selects port

server.start()
print(f"Server bound to port: {server.port}")
print(f"Full URL: {server.url}")

If you need to use a specific port, explicitly pass it to avoid conflicts:

server = Server(port=8890)  # Use a known free port

server.start()

Diagnosing Database and Health Check Failures

Once the server responds to HTTP requests, the next layer to troubleshoot is database connectivity, which is exposed through the health endpoint.

Interpreting 503 Errors from the Health Endpoint

The /health endpoint is defined in hindsight-api-slim/hindsight_api/api/http.py (lines 55-66). It returns HTTP 200 when healthy or HTTP 503 when the internal MemoryEngine cannot communicate with PostgreSQL:

curl http://127.0.0.1:<port>/health

• HTTP 200: Returns { "status": "healthy", "database": "connected" }
• HTTP 503: Returns JSON with "status": "unhealthy" and an "error" field describing the failure

The endpoint delegates its check to app.state.memory.health_check(), which validates that the database connection pool is initialized and responsive.

Database Connection Verification

The health check implementation resides in hindsight-api-slim/hindsight_api/engine/memory_engine.py at lines 92-101. The MemoryEngine.health_check() method executes a SELECT 1 query against the connection pool:

# Conceptual flow from memory_engine.py lines 92-101

async def health_check(self):
    try:
        await self.pool.execute("SELECT 1")
        return {"status": "healthy", "database": "connected"}
    except Exception as e:
        return {"status": "unhealthy", "database": "error", "error": str(e)}

If you see a 503 response with a database error, verify your HINDSIGHT_API_DATABASE_URL environment variable. If you are using the embedded pg0 PostgreSQL instance (the default), ensure the binary is present and the process has permission to create temporary data directories, typically under /tmp/pg0.

Configuration and Environment Verification

Misconfigured environment variables are a common source of connectivity issues. The server reads configuration from hindsight-api-slim/hindsight_api/config.py via the get_config() function.

Critical Environment Variables

Check these variables against your deployment environment:

• HINDSIGHT_API_HOST: Interface to bind (default: 127.0.0.1)
• HINDSIGHT_API_PORT: Explicit port number (overrides auto-selection)
• HINDSIGHT_API_BASE_PATH: URL prefix for all routes (e.g., /hindsight)
• HINDSIGHT_API_DATABASE_URL: PostgreSQL connection string
• HINDSIGHT_API_LOG_LEVEL: Set to debug for verbose output

You can inspect the active configuration programmatically:

from hindsight_api.config import get_config
print(get_config())

The .env.example file in the repository root enumerates all available variables and their default values, serving as a reference for proper configuration.

Reverse Proxy and Base Path Issues

When deploying behind Nginx, Traefik, or similar proxies, base path mismatches cause 404 errors that appear as connection failures.

The FastAPI application respects app.root_path, which is set from config.base_path in hindsight-api-slim/hindsight_api/api/http.py. When you configure a custom base path, the health endpoint moves accordingly. As noted in the test suite at hindsight-api-slim/tests/test_base_path.py (lines 55-59), a base path of /hindsight means the health check is accessible at /hindsight/health, not /health.

Verify your proxy configuration matches HINDSIGHT_API_BASE_PATH:

# Nginx example

location /hindsight/ {
    proxy_pass http://127.0.0.1:8000/hindsight/;
}

Step-by-Step Troubleshooting Workflow

Follow this systematic approach to isolate connection issues:

1. Start the server and monitor logs

   from hindsight import Server
   import logging
   
   logging.basicConfig(level=logging.DEBUG)
   server = Server()
   server.start()  # Blocks until ready
   

   Look for the "Hindsight server started" confirmation message.

2. Test connectivity with curl

   curl -v http://127.0.0.1:<port>/health

   Replace <port> with the value from server.port.

3. Analyze health check response

   If you receive HTTP 503, examine the JSON error field to determine if the issue is database authentication, network unreachable, or pool exhaustion.

4. Verify port availability

   ss -ltnp | grep <port>

   If another process holds the port, restart Hindsight with a different port number.

5. Enable debug logging

   export HINDSIGHT_API_LOG_LEVEL=debug
   python your_server_script.py

   This reveals detailed startup sequences, including PostgreSQL initialization and LLM client creation.

6. Run integration tests

   pytest hindsight-api-slim/tests/test_http_api_integration.py

   These tests spin up an in-process server and validate the health endpoint, providing a clean-room verification of your environment.

Summary

• Server startup failures are indicated by the absence of the "Hindsight server started" log message in hindsight-all/hindsight/server.py; check for exceptions during Server.start().
• Port conflicts can be avoided by using the auto-selection feature (port=None) or explicitly specifying a free port; verify with server.port after initialization.
• Database issues manifest as HTTP 503 responses from /health with detailed error messages from MemoryEngine.health_check() in hindsight-api-slim/hindsight_api/engine/memory_engine.py.
• Environment configuration is centralized in hindsight-api-slim/hindsight_api/config.py; validate variables like HINDSIGHT_API_DATABASE_URL and HINDSIGHT_API_BASE_PATH against your deployment topology.
• Reverse proxy setups require matching HINDSIGHT_API_BASE_PATH with the proxy's forwarding rules to ensure the /health endpoint is accessible at the correct path.

Frequently Asked Questions

Why does my Hindsight server return a 503 error on the health endpoint?

A 503 status indicates the MemoryEngine cannot communicate with the PostgreSQL database. According to the implementation in hindsight-api-slim/hindsight_api/engine/memory_engine.py, the health check runs SELECT 1 against the connection pool; if this query fails due to missing HINDSIGHT_API_DATABASE_URL, network issues, or authentication errors, the endpoint returns {"status": "unhealthy", "database": "error", "error": "<message>"}. Check your database URL and ensure PostgreSQL is reachable.

How do I check if the Hindsight server is using the correct port?

After calling server.start(), inspect the server.port attribute. In hindsight-all/hindsight/server.py, the Server class sets self.port = port or _find_free_port() during initialization. If you passed port=None, the system selected an available ephemeral port automatically. The complete URL is available via server.url, which is also logged as "Hindsight server started at {self.url}".

What should I do if the embedded PostgreSQL (pg0) fails to start?

First, ensure the pg0 binary is present in your environment and executable. The embedded database requires permission to create temporary data directories, typically under /tmp/pg0. Set HINDSIGHT_API_LOG_LEVEL=debug to see detailed startup logs from the pg0 initialization sequence. If problems persist, switch to an external PostgreSQL instance by setting HINDSIGHT_API_DATABASE_URL to a valid connection string instead of relying on the embedded default.

How do I configure Hindsight to work behind a reverse proxy like Nginx?

Set the HINDSIGHT_API_BASE_PATH environment variable to match the path prefix configured in your proxy. For example, if Nginx forwards requests from /hindsight/ to the Hindsight server, set HINDSIGHT_API_BASE_PATH=/hindsight. The FastAPI app assigns this to app.root_path, ensuring that internal routing and the /health endpoint respond correctly at /hindsight/health rather than the root path. Verify this configuration using the test patterns shown in hindsight-api-slim/tests/test_base_path.py.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}