Cannot connect Droplet to MongoDB in VPC despite firewall rules and trusted sources

Hi, I’m encountering a MongooseServerSelectionError: Server selection timed out after 30000 ms when attempting to connect my server application (running on a Droplet) to a DigitalOcean managed MongoDB instance.

Here’s my setup:

• Environment: Both the Droplet and the MongoDB instance are within the same VPC.
• Firewall Configuration: I have an outbound rule on the Droplet’s firewall allowing TCP traffic on port 27017 to the VPC IP range.
• MongoDB Trusted Sources: I have added the tag associated with my Droplet to the MongoDB instance’s trusted sources.
• Connection String: I am using the VPC connection string provided by DigitalOcean in my Mongoose adapter.

The Issue:

Despite these configurations, the connection consistently fails with the MongooseServerSelectionError.

Observation:

The only scenario where the connection is successful is when I temporarily configure the Droplet’s outbound firewall rule for port 27017 to allow traffic to “All IPv4 Addresses”. This is not a desirable long-term solution.

Question:

Could someone please help me identify what I might be missing or misconfiguring that prevents the connection from working correctly within the VPC? What further troubleshooting steps can I take to resolve this issue and establish a secure connection using the VPC?

Any insights or suggestions would be greatly appreciated!

Thanks.