I'm deploying an AWS Lambda function that connects to a MySQL database hosted on AWS RDS. However, when I invoke the function, I get the following error message:

{
    "success": false,
    "message": "Unable to connect to any of the specified MySQL hosts"
}

Issue: The same connection string and credentials work perfectly when I run the application locally.

The RDS instance is publicly accessible and allows connections from my local machine.

I am using ASP.NET Core with MySQL.

Connection String in appsettings.json

"ConnectionStrings": {
   "DefaultConnection": "Server=anikafashionhose2update.cm7a0ysyejex.us-east-1.rds.amazonaws;Port=3306;Database=anikafashionhouse3;User=admin;Password=admin1998;"
}

I'm deploying an AWS Lambda function that connects to a MySQL database hosted on AWS RDS. However, when I invoke the function, I get the following error message:

{
    "success": false,
    "message": "Unable to connect to any of the specified MySQL hosts"
}

Issue: The same connection string and credentials work perfectly when I run the application locally.

The RDS instance is publicly accessible and allows connections from my local machine.

I am using ASP.NET Core with MySQL.

Connection String in appsettings.json

"ConnectionStrings": {
   "DefaultConnection": "Server=anikafashionhose2update.cm7a0ysyejex.us-east-1.rds.amazonaws;Port=3306;Database=anikafashionhouse3;User=admin;Password=admin1998;"
}

• mysql
• amazon-web-services
• aws-lambda
• asp-core-webapi
• amazon-rds

• 4 If those are the actual connection settings for your database server, then you should assume at this point that your database has been accessed by other people and it needs to be deleted and recreated with a new admin password. – Mark B Commented 2 days ago
• 1 As to the Lambda function connection issue, is the Lambda function configured to run in a VPC or not? – Mark B Commented 2 days ago

1 Answer 1

This error typically happens because Lambda and RDS have different networking configurations. Here are the most common fixes:

1. Security Group Issue: Add an inbound rule to your RDS security group to allow MySQL traffic (port 3306) from your Lambda's security group.

2. VPC Configuration: Ensure your Lambda is configured to run in the same VPC as your RDS instance. Lambda → Configuration → VPC.

3. Subnet Configuration: Make sure Lambda is using subnets that can reach your RDS instance.

4. Connection Pooling: In Lambda, use a static connection object to avoid connection issues during cold starts:

private static readonly MySqlConnection _connection = new MySqlConnection(connectionString);

// Check connection before use
if (_connection.State != ConnectionState.Open)
{
    await _connection.OpenAsync();
}