Unable to connect to any of the specific MySQL hosts with AWS Lambda to RDS MySQL

Question

I have an AWS Lambda function for an API. I have a test function inside of the API that returns a "Success" string so I know that I can hit the API from my machine (Postman).

The Lambda API is inside of my VPC. I have public and private subnets. The API is living in the public subnets. I also have a RDS database that's living in the private subnets. I can connect to the database through a Bastion host so I know the database is connected and working.

When I try an API call that connects to the database, I can see an error in CloudWatch that says:

[Error] Amazon.Lambda.AspNetCoreServer.APIGatewayProxyFunction: Unknown error responding to request: MySqlException: MySql.Data.MySqlClient.MySqlException (0x80004005): Unable to connect to any of the specified MySQL hosts. ---> System.InvalidOperationException: Sequence contains more than one matching element

There's a lot of references to that error message that talks about the Linq SingleOrDefault() method, but I don't have any references to that method.

I think that error has something to do with the security groups. I have an RDS security group that has an inbound rule on port 3306 from my internal VPC ip addresses.

The security group for my Lambda function should be ok since I can successfully hit the test route.

Finally, I tried connecting to the database through the API in debug on my machine and I get an error "The requested name is valid, but no data of the requested type was found"

Does anyone have any other ideas or places to look?

@aviboy2006 I'm not using either. I don't need to initiate traffic to the internet from the private subnets, only to the Lambda living in the public subnets. — John Rousseau, Dec 18 '19 at 07:09
Allowing inbound traffic on DB from internet is not recommended and should always be avoided you added this ? this is new error you getting ? — Avinash Dalvi, Dec 18 '19 at 07:14
It's not a new error. I just dug into the CloudWatch details a little more. I'm not allowing inbound traffic on DB. Inbound rules are 10.0.* and the SG from Lambda. — John Rousseau, Dec 18 '19 at 07:17

Avinash Dalvi · Answer 1 · 2019-12-18T07:10:10.810

0

Can you check your this setting is enable or not for RDS Security group ?

Disclaimer : Allowing inbound traffic on DB from internet is not recommended and should always be avoided

edited Dec 18 '19 at 07:10

answered Dec 18 '19 at 06:41

Avinash Dalvi

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My inbound rules are TCP 3306 for my VPC IP addresses and for the SG for my Lambda function. Outbound rules are all traffic. – John Rousseau Dec 18 '19 at 06:54
you are having separate SG for both RDS and Lambda ? – Avinash Dalvi Dec 18 '19 at 07:09
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Please add a disclaimer in the answer. Allowing inbound traffic on DB from internet is not recommended and should always be avoided. It should have proper sourceIP/ SG values. – Ankit Deshpande Dec 18 '19 at 07:09
@aviboy2006 I have seperate SG for Lambda and RDS. Lambda inbound is from my local machine for testing and the IP of the web server. Outbound is all traffic. – John Rousseau Dec 18 '19 at 07:11
have u assigned lambda two subnet one is lambda specfic and one for RDS specific ? – Avinash Dalvi Dec 18 '19 at 07:25
Did you ever fiind the solution to this? I am running into same issue at the moment. Thanks! – Taylor Goodall AU Feb 18 '20 at 02:43

score 0 · Answer 2 · answered Aug 16 '22 at 07:37

My RDS database (that I was trying to connect to and read from using AWS Lambda) was also a MySQL database.

When I tested the Lambda function I was getting 'Unable to connect to any of the specified MySQL hosts' (after waiting -- like it was timing-out).

I reviewed the answer from @aviboy2006, which helped me. I tried all the Security Group rules shown in that answer. I found I was able to successfully connect-to and read from the RDS MySQL database when I defined both an Inbound and Outbound rule for the associated VPC Security Group as

Type: MYSQL/Aurora
Protocol: TCP
Port Range: 3306
Source: Custom: 0.0.0.0/0

Unable to connect to any of the specific MySQL hosts with AWS Lambda to RDS MySQL

2 Answers2

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