Security Group (SG) and Network Access Control List (NACL) configurations for Elastic Kubernetes Service (EKS)

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.

Emmanuel Lilette

Emmanuel Lilette

Emmanuel is a Site Reliability Engineer (SRE) at Padok. He is one of our architect specialized in cloud (AWS and GCP) and load testing using Gatling tool.

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