I was looking for firewall good practices for an EKS cluster. I easily found AWS recommendations about Security Groups (SG) but I had trouble finding some for Network Access Control List (NACLs). I realized it is not so easy to derive NACL configuration from an SG configuration if you do not understand some core concepts. In this article I will try to sum up these concepts by comparing SGs and NACLs. I will then propose some configurations for both resources in case you are hosting an EKS cluster.
Difference between NACLs and SGs
NACL and SG are both firewall rules, however they have notable differences that I have summarized in the following table:
| NACL | SG | |
| Scopes | subnet or VPC - applies to all instances in the subnet or VPC | instance - applies to all instances linked to the SG |
| Cardinality | 1 NACL per subnet or VPC | 1 to many SG per instance or instance group |
| Actions | allow or deny | allow - every unspecified rule defaults to deny |
| States | stateless - i.e. NACLs allow traffic looking at the IP and port regardless of the fact that it is a reply request | statefull - i.e. SGs automatically allow a reply to be returned. They maintain a state table that tracks the origin and destination IP and port. Only one rule (inbound or outbound) is required |
| Rule order | rules are applied in order | rules are applied simultaneously |
Note that inbound traffic first passes through the NACL firewalls then to the SG firewalls. Outbound traffic goes the opposite way.
Firewall requirement for EKS
The AWS documentation specifies the following requirements:
- traffic needs to be allowed between the control plane and managed node groups
- traffic needs to be allowed between nodes
- nodes and control plane should have outbound access to the internet.
Note that one of the possibilities your nodes might not join your cluster is if they do not have access to the internet. Indeed, they need access to the Amazon EKS API.
SG configuration for EKS
Taking into account above consideration, here is an SG proposition for EKS.
Inbound
| Protocol | Port | Source |
| TCP | 443 | self |
| TCP | 1024 - 65535 | self |
Outbound
| Protocol | Port | Destination |
| TCP | 443 | 0.0.0.0/0 |
| TCP | 80 | 0.0.0.0/0 |
| TCP | 1024 - 65535 | 0.0.0.0/0 |
NACL configuration for EKS
Taking into account above consideration, here is a NACL proposition for EKS.
Inbound
| Rule # | Protocol | Port | Source | Allow / Deny |
| 100 | TCP | All | self | Allow |
| 200 | TCP | 1024 - 65535 | 0.0.0.0/0 | Allow |
| 9000 | All | All | All | Deny |
Outbound
| Rule # | Protocol | Port | Destination | Allow / Deny |
| 100 | TCP | All | self | Allow |
| 200 | TCP | 1024 - 65535 | 0.0.0.0/0 | Allow |
| 300 | TCP | 80 | 0.0.0.0/0 | Allow |
| 400 | TCP | 443 | 0.0.0.0/0 | Allow |
| 9000 | All | All | All | Deny |
I hope this article will help you set up your EKS security group (SG) and network access control list (NACL) firewalls easily. If you have other recommendations, questions or challenges please reach me in the comment section. Take care.