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I have one EC2 instance that can connect to RDS, and another that can't.

  • They are in the same VPC/Subnet/AZ
  • They have the same IAM role
  • They have different (but similar) security groups, both allow all inbound
  • The subnets are showing in the configuration for the RDS instance
  • The ec2 instance that can't connect just times out

What could be going wrong? Is there any way to work out where the connection is failing?

user31415629
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  • The security groups allow *all* inbound? And you left the outbound rules alone (I hope)? And you left the VPC Network ACLs alone, at their defaults? And if you type `dig the-rds-hostname +short` you get a private IP in response, and that IP is on the same subnet? – Michael - sqlbot May 11 '17 at 01:52
  • Check out this link http://stackoverflow.com/questions/32158216/what-would-prevent-me-from-connecting-to-a-mysql-server-on-aws-rds-from-an-aws-e/41711490#41711490 – Kumaresh Babu N S May 11 '17 at 03:36
  • Could you please show your RDS Inbound security group and both of the EC2 outbound security groups? (Just Edit your question to include them.) – John Rotenstein May 11 '17 at 05:29

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