How to find unused Amazon EC2 security groups

Question

I'm try to find a way to determine orphan security groups so I can clean up and get rid of them. Does anyone know of a way to discover unused security groups. Either through the console or with the command line tools will work (Running command line tools on Linux and OSX machines).

Accepted Answer

Note: this only considers security use in EC2, not other services like RDS. You'll need to do more work to include security groups used outside EC2. The good thing is you can't easily (might not even be possible) to delete active security groups if you miss one associated w/another service.

Using the newer AWS CLI tool, I found an easy way to get what I need:

First, get a list of all security groups

```
aws ec2 describe-security-groups --query 'SecurityGroups[*].GroupId'  --output text | tr '	' '
'
```

Then get all security groups tied to an instance, then piped to `sort` then `uniq`:

```
aws ec2 describe-instances --query 'Reservations[*].Instances[*].SecurityGroups[*].GroupId' --output text | tr '	' '
' | sort | uniq
```

Then put it together and compare the 2 lists and see what's not being used from the master list:

How to find unused Amazon EC2 security groups

Solution

Problem