使用外部EC2服务器作为签名处理器向S3上传文件报错求助

Hey there, let's work through your Fine Uploader S3 signing issues step by step. From the error logs you shared, the most critical problem is the connection refusal to your signature server—let's start there, then cover the other details.

Key Issues & Fixes #

1. Fix the ERR_CONNECTION_REFUSED Error (Core Problem) #

The error OPTIONS https://my-external-signature-server/ net::ERR_CONNECTION_REFUSED means your frontend can't reach your Flask signature server at all. Here's what to check:

• Verify the signature server URL: Double-check that the endpoint value in your signature config points to the correct public URL of your Flask app. If you're running Flask on the default port (5000), don't forget to include it (e.g., https://my-real-server.com:5000).
• Check firewall/security group rules: Make sure your server's firewall or cloud provider security group allows incoming traffic on the port your Flask app is listening on. Also, ensure it permits CORS preflight requests (the OPTIONS method) from your frontend's domain.
• Test server accessibility directly: Use curl or your browser to send an OPTIONS request to your signature server URL (e.g., curl -X OPTIONS https://your-real-signature-server-url/). If this fails, your server isn't properly deployed or reachable—check if Flask is running, if your reverse proxy (like Nginx) is configured correctly, or if there's a DNS issue.

2. Strategy Document & Flask Setup Confirmation #

You don't need to manually create a policy document—the Flask example's app.py handles generating and signing the policy automatically. But you must confirm:

• You've correctly set all required AWS parameters in your Flask app (like AWS_SECRET_ACCESS_KEY, S3_BUCKET_NAME, and AWS_REGION). These are usually set via environment variables or directly in the code (though environment variables are safer).
• The Flask app's routes match what Fine Uploader expects. The example uses / for the signature endpoint and /s3/success for the upload success endpoint, which aligns with your frontend config—so that part should be okay if you didn't modify the routes.

3. Minor UI Error (Can Be Ignored) #

The GET https://cdn.shopify.com/...edit.gif 404 error is just Fine Uploader failing to load its default edit icon. This doesn't affect upload functionality, but if you want to fix it, you can specify a custom icon path using the editFile.icon option in your Fine Uploader config.

Debugging Tips #

• Use your browser's DevTools (Network tab) to inspect the failed OPTIONS request. Check if the Origin header matches what your server allows, and if the server returns proper CORS headers (like Access-Control-Allow-Origin and Access-Control-Allow-Methods).
• Check your Flask server's logs. If you don't see any incoming requests, the problem is network-related. If you see errors in the logs, they'll point to issues like missing AWS credentials or invalid bucket settings.

内容的提问来源于stack exchange，提问作者Christian