Eks Networking Explained for Kubernetes Users
Understanding Networking in EKS
EKS networking is a crucial aspect of deploying Kubernetes clusters on AWS, ensuring seamless communication between Pods, services, and external systems. Kubernetes follows a well-defined networking model where every Pod gets its own IP address, eliminating the need for NAT (Network Address Translation). Containers within a Pod share the same IP, allowing inter-container communication via localhost. Moreover, Kubernetes uses network policies to control traffic between Pods, ensuring security and compliance.
For networking in Kubernetes, the Container Network Interface (CNI) specification plays a vital role. It allows different plugins to configure networking efficiently, and in EKS, AWS VPC CNI is the default implementation. This CNI ensures Pods receive IPs from the AWS VPC, seamlessly integrating Kubernetes networking with AWS infrastructure.
Network Implementation in Kubernetes
A Pod is the smallest deployable unit in Kubernetes, consisting of one or more containers. These containers share a network namespace, enabling them to communicate using localhost. Kubernetes networking involves various types of communication:
– Pod-to-Pod Communication: Direct communication via Pod IPs within the cluster.
– Container-to-Container Communication: Containers inside a Pod communicate over localhost.
Kubernetes networking is built to be simple yet scalable, allowing workloads to function without complex NAT or port mapping.
AWS VPC Basics for EKS Networking
Before delving into EKS networking specifics, understanding AWS Virtual Private Cloud (VPC) networking is essential. AWS Regions contain multiple Availability Zones (AZs), each consisting of data centers connected by high-speed networks. A VPC defines an isolated network environment using an IP range (CIDR).
Key AWS Networking Components:
– Subnets: Segments of a VPC, each associated with a single AZ.
– Elastic Network Interface (ENI): A virtual network interface attached to EC2 instances, allowing multiple IPs per instance.
– Internet Gateway (IGW): Enables public internet access for resources in the VPC.
– NAT Gateway (NATGW): Provides outbound internet access for private resources.
– Transit Gateway (TGW): Facilitates communication between multiple VPCs and on-premises networks.
AWS supports private addressing using CIDR ranges such as:
– 10.0.0.0 – 10.255.255.255 (10/8)
– 172.16.0.0 – 172.31.255.255 (172.16/12)
– 192.168.0.0 – 192.168.255.255 (192.168/16)
These networking fundamentals form the backbone of EKS networking.
EKS Networking Overview
Amazon EKS is a managed Kubernetes service where the control plane runs in an AWS-managed VPC. This setup raises two key questions for networking:
1. How do external clients access the Kubernetes API?
2. How do Pods communicate with other resources?
AWS VPC CNI for EKS
The AWS VPC CNI plugin is the default networking solution for EKS. It integrates with AWS networking, allowing Pods to receive IPs directly from the VPC CIDR block. Each worker node has a limited number of Elastic Network Interfaces (ENIs), with each ENI supporting multiple IPs.
For example, an m4.4xlarge instance supports up to 8 ENIs, each capable of handling 30 IP addresses, resulting in a total of 240 Pod IPs per node.
Configuring EKS Networking Using AWS VPC CNI
To configure EKS networking, you need to manage the CNI plugin effectively. Here are some key aspects:
Managing the CNI Plugin: The AWS VPC CNI plugin allows Pods to receive IP addresses from the VPC. You can manage this plugin using the `kubectl` command-line tool.
Disabling CNI Source NAT: By default, the CNI plugin performs source NAT for outbound traffic. If you want to use an external NAT device, you can disable this behavior using the following command:
“`bash
kubectl set env daemonset aws-node -n kube-system AWS_VPC_K8S_CNI_EXTERNALSNAT=true
“`
Configuring Custom Networking: Custom networking allows you to use different security groups or subnets within the same VPC. To enable this, configure the required security groups and subnets in your VPC. Then, run:
“`bash
kubectl set env daemonset aws-node -n kube-system AWS_VPC_K8S_CNI_CUSTOM_NETWORK_CFG=true
“`
You will also need to create an ENIConfig file that defines the required subnets and security groups.
Common EKS Networking Issues and Solutions
Networking in Kubernetes can be complex. Various issues may arise. Here are some common issues and their solutions:
Worker Nodes Cannot Join the Cluster:
Solution: Check that the worker nodes’ subnets have IP access to the internet. Verify the route tables and associated security groups.
Pods Cannot Be Assigned an IP Address from the VPC:
Solution: Ensure that the VPC has enough free IP addresses. If not, assign a secondary CIDR range or enable prefix addressing.
Pods Unable to Resolve K8S DNS Names:
Solution: Ensure that all worker node subnets do not have any security groups blocking port 53. Ensure that your VPC has `enableDNSHostnames` and `enableDNSSupport` set to true.
AWS Load Balancers Cannot Be Deployed:
Solution: Ensure that the worker node subnets are tagged with `kubernetes.io/role/elb` or `kubernetes.io/role/internal-elb`.
Conclusion: Building Your First EKS Cluster
EKS networking is a critical component of Kubernetes deployments on AWS. A strong grasp of both Kubernetes networking principles and AWS VPC fundamentals ensures optimal cluster performance. By leveraging the AWS VPC CNI plugin, developers can manage Pod networking efficiently, providing seamless communication across workloads.
Understanding custom networking, security groups, and IP address allocation is essential for scaling EKS clusters. Additionally, addressing common networking challenges ensures a reliable and secure environment for containerized applications.
If you’re getting started with Kubernetes on AWS, mastering EKS networking will empower you to build your first EKS cluster with confidence.
Do you like to read more educational content? Read our blogs at Cloudastra Technologies or contact us for business enquiry at Cloudastra Contact Us.