[jcrites]

> The documentation suggests adding the AmazonEC2RoleforSSM policy to the role of the EC2 instances

Which documentation do you mean? The article mentions the policy AmazonSSMManagedInstanceCore, which is the same as what's mentioned in the SSM setup guide:

https://docs.aws.amazon.com/systems-manager/latest/userguide...

[mishappen]

Thanks for clarifying, I didn’t recheck since we rolled out SSM in mid-2019 and then scrambled when we realised we’d granted account wide S3 permissions. The article I linked to also has a recommended minimal IAM policy for Run Command and SSM. I’ll update my comment to mention this.

[mishappen]

It looks like the docs were update in June 2019 (https://github.com/awsdocs/aws-systems-manager-user-guide/co...)

[x3n0ph3n3]

AmazonSSMManagedInstanceCore is still too much access, it has unscoped ssm:GetParameter! I hope you weren't trying to protect any secrets in ParameterStore!

[acdha]

Doesn’t that still fail if you don’t also have the corresponding decrypt KMS permission?