Are security groups enforced when using ssm start-session with port forwarding

Question

Can you tell me if security groups are still enforced when we connect to an instance via the ssm start-session CLI command using the port forwarding option

Or are security groups bypassed when connecting to instances using the ssm CLI ?

Answer

The security groups are not bypassed, however, the SSM agent on the instance initiates the the connection to the SSM service so the outbound rules of the security group on the instance are the ones in play. Most likely, the outbound is wide open. Minimally, the outbound rule needs to allow outbound 443 to the SSM endpoints. See: [Systems Manager prerequisites](https://docs.aws.amazon.com/systems-manager/latest/userguide/systems-manager-prereqs.html).

```
(Recommended) Create a VPC endpoint in Amazon Virtual Private Cloud (Amazon VPC) to use with Systems Manager.
If you don't use a VPC endpoint, configure your managed instances to allow HTTPS (port 443) outbound traffic to the Systems Manager endpoints. For information, see (Optional) Create a VPC endpoint.
```

Are security groups enforced when using ssm start-session with port forwarding

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