EKS Prefix Delegation - IP Planning Guide

kubectl get nodes -o custom-columns=NAME:.metadata.name,CAPACITY:.status.capacity.pods,ALLOCATABLE:.status.allocatable.pods,AGE:.metadata.creationTimestamp

📊 Your Subnet Configuration

Subnet	CIDR	Available IPs	Availability Zone
Subnet 1	`10.50.64.0/20`	4,096 IPs	AZ-1
Subnet 2	`10.50.112.0/20`	4,096 IPs	AZ-2
Subnet 3	`10.50.16.0/20`	4,096 IPs	AZ-3

Total Available: ~12,288 IPs across all subnets

🔄 How Prefix Delegation Works

Traditional Secondary IP Mode (Before)

Node ENI → Requests individual IPs
├─ Primary IP: 1 IP (for node)
├─ Secondary IP: 1 IP (for pod 1)
├─ Secondary IP: 1 IP (for pod 2)
└─ Secondary IP: 1 IP (for pod 3)

Prefix Delegation Mode (Now)

Node ENI → Requests /28 prefix (16 IPs at once)
├─ Primary IP: 1 IP (for node)
├─ Prefix 1: /28 = 16 IPs (for 16 pods)
├─ Prefix 2: /28 = 16 IPs (for 16 pods)
└─ Prefix 3: /28 = 16 IPs (for 16 pods)

🖥️ Your Node Configuration (m6g.large)

Network Interface Limits:

ENIs per node: 3 ENIs maximum
Prefixes per ENI: 16 prefixes (with prefix delegation)
IPs per prefix: 16 IPs (/28 CIDR block)

IP Allocation per Node:

m6g.large Node
├─ ENI 0 (Primary)
│   ├─ 1 Primary IP (node itself)
│   └─ Up to 16 prefixes × 16 IPs = 256 IPs
│
├─ ENI 1 (Secondary)
│   └─ Up to 16 prefixes × 16 IPs = 256 IPs
│
└─ ENI 2 (Secondary)
    └─ Up to 16 prefixes × 16 IPs = 256 IPs

Total theoretical: 1 + (3 ENIs × 16 prefixes × 16 IPs) = 769 IPs

But Kubernetes limits it to ~110 pods per node (kubelet default)

💡 How Your Configuration Works

With WARM_PREFIX_TARGET = “1”

When a node starts:

Initial allocation: Requests 1 prefix (/28 = 16 IPs) per ENI
- 3 ENIs × 1 prefix × 16 IPs = 48 IPs reserved initially
- Plus 1 primary IP for node = 49 IPs per node
As pods are scheduled:
- When 15 out of 16 IPs in a prefix are used
- VPC CNI requests another /28 prefix (16 more IPs)
- Keeps 1 “warm” prefix ready at all times
Maximum allocation per node:
- Up to 110 pods (Kubernetes limit)
- Each pod = 1 IP
- Actual IPs requested = ~7-8 prefixes × 16 = 112-128 IPs per node

📈 Your Capacity Calculation

Current Node Group (1-2 nodes):

Nodes	IPs Used (Initial)	IPs Used (Full)	Subnet Impact
2 nodes	2 × 49 = 98 IPs	2 × 128 = 256 IPs	Minimal

Scaled Node Group (Max capacity scenarios):

Let’s calculate different scenarios:

Scenario 1: 10 Nodes

Initial: 10 × 49 = 490 IPs
Full capacity: 10 × 128 = 1,280 IPs
Pods: 10 × 110 = 1,100 pods

Scenario 2: 50 Nodes

Initial: 50 × 49 = 2,450 IPs
Full capacity: 50 × 128 = 6,400 IPs
Pods: 50 × 110 = 5,500 pods

Scenario 3: 100 Nodes

Initial: 100 × 49 = 4,900 IPs
Full capacity: 100 × 128 = 12,800 IPs
Pods: 100 × 110 = 11,000 pods

✅ Your Subnet Capacity Assessment

Per Subnet (each /20):

Available IPs per subnet: 4,096
Maximum nodes per subnet (at full capacity): ~32 nodes
Maximum pods per subnet: 32 × 110 = ~3,520 pods

Total Capacity (all 3 subnets):

Total Available IPs: 12,288
Maximum nodes (distributed): ~96 nodes
Maximum pods: 96 × 110 = ~10,560 pods

🎯 Your Configuration is EXCELLENT! ✅

Why Your Setup Works Well:

✅ Large Subnets: /20 subnets are very generous
✅ Multiple AZs: Distributes load across 3 availability zones
✅ Room to Grow: Can support ~30 nodes per subnet
✅ Prefix Efficiency: /28 prefixes align well with your subnet size

🔍 Real-World Example

Let’s say you have 2 nodes (current config):

Node 1 in Subnet 1 (10.50.64.0/20):

- Node IP: 10.50.64.10
- Prefix 1 (ENI 0): 10.50.64.16/28 → 10.50.64.16 - 10.50.64.31 (16 IPs)
- Prefix 2 (ENI 1): 10.50.64.32/28 → 10.50.64.32 - 10.50.64.47 (16 IPs)
- Prefix 3 (ENI 2): 10.50.64.48/28 → 10.50.64.48 - 10.50.64.63 (16 IPs)

Node 2 in Subnet 2 (10.50.112.0/20):

- Node IP: 10.50.112.10
- Prefix 1 (ENI 0): 10.50.112.16/28 → 10.50.112.16 - 10.50.112.31 (16 IPs)
- Prefix 2 (ENI 1): 10.50.112.32/28 → 10.50.112.32 - 10.50.112.47 (16 IPs)
- Prefix 3 (ENI 2): 10.50.112.48/28 → 10.50.112.48 - 10.50.112.63 (16 IPs)

Each pod gets one IP from these prefixes automatically!

📋 Recommendations

✅ You’re Good to Go!

Your current setup can comfortably support:

Short term: 2-10 nodes (your current plan)
Medium term: 20-30 nodes per subnet
Long term: Up to ~90 nodes total

Optional Optimizations:

If you want to be even more efficient, you could adjust WARM_PREFIX_TARGET:

# More aggressive (saves IPs)
WARM_PREFIX_TARGET = "0"  # Request prefixes only when needed

# Current (balanced)
WARM_PREFIX_TARGET = "1"  # Keep 1 warm prefix ready

# More prefixes (faster pod startup)
WARM_PREFIX_TARGET = "2"  # Keep 2 warm prefixes ready

🚀 Summary

You have PLENTY of IP space! Your /20 subnets are well-sized for prefix delegation. With your current 2-node setup, you’re using less than 0.5% of your subnet capacity. Even scaling to 50+ nodes would still be comfortable.

📚 Additional Resources

AWS VPC CNI Prefix Delegation: https://docs.aws.amazon.com/eks/latest/userguide/cni-increase-ip-addresses.html
ENI Limits by Instance Type: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-eni.html
EKS Best Practices: https://aws.github.io/aws-eks-best-practices/

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PrefixDelegation

EKS Prefix Delegation - IP Planning Guide

📊 Your Subnet Configuration

🔄 How Prefix Delegation Works

Traditional Secondary IP Mode (Before)

Prefix Delegation Mode (Now)

🖥️ Your Node Configuration (m6g.large)

Network Interface Limits:

IP Allocation per Node:

💡 How Your Configuration Works

With WARM_PREFIX_TARGET = “1”

📈 Your Capacity Calculation

Current Node Group (1-2 nodes):

Scaled Node Group (Max capacity scenarios):

Scenario 1: 10 Nodes

Scenario 2: 50 Nodes

Scenario 3: 100 Nodes

✅ Your Subnet Capacity Assessment

Per Subnet (each /20):

Total Capacity (all 3 subnets):

🎯 Your Configuration is EXCELLENT! ✅

Why Your Setup Works Well:

🔍 Real-World Example

Node 1 in Subnet 1 (10.50.64.0/20):

Node 2 in Subnet 2 (10.50.112.0/20):

📋 Recommendations

✅ You’re Good to Go!

Optional Optimizations:

🚀 Summary

📚 Additional Resources

​EKS Prefix Delegation - IP Planning Guide

​📊 Your Subnet Configuration

​🔄 How Prefix Delegation Works

​Traditional Secondary IP Mode (Before)

​Prefix Delegation Mode (Now)

​🖥️ Your Node Configuration (m6g.large)

​Network Interface Limits:

​IP Allocation per Node:

​💡 How Your Configuration Works

​With WARM_PREFIX_TARGET = “1”

​📈 Your Capacity Calculation

​Current Node Group (1-2 nodes):

​Scaled Node Group (Max capacity scenarios):

​Scenario 1: 10 Nodes

​Scenario 2: 50 Nodes

​Scenario 3: 100 Nodes

​✅ Your Subnet Capacity Assessment

​Per Subnet (each /20):

​Total Capacity (all 3 subnets):

​🎯 Your Configuration is EXCELLENT! ✅

​Why Your Setup Works Well:

​🔍 Real-World Example

​Node 1 in Subnet 1 (10.50.64.0/20):

​Node 2 in Subnet 2 (10.50.112.0/20):

​📋 Recommendations

​✅ You’re Good to Go!

​Optional Optimizations:

​🚀 Summary

​📚 Additional Resources

EKS Prefix Delegation - IP Planning Guide

📊 Your Subnet Configuration

🔄 How Prefix Delegation Works

Traditional Secondary IP Mode (Before)

Prefix Delegation Mode (Now)

🖥️ Your Node Configuration (m6g.large)

Network Interface Limits:

IP Allocation per Node:

💡 How Your Configuration Works

With WARM_PREFIX_TARGET = “1”

📈 Your Capacity Calculation

Current Node Group (1-2 nodes):

Scaled Node Group (Max capacity scenarios):

Scenario 1: 10 Nodes

Scenario 2: 50 Nodes

Scenario 3: 100 Nodes

✅ Your Subnet Capacity Assessment

Per Subnet (each /20):

Total Capacity (all 3 subnets):

🎯 Your Configuration is EXCELLENT! ✅

Why Your Setup Works Well:

🔍 Real-World Example

Node 1 in Subnet 1 (10.50.64.0/20):

Node 2 in Subnet 2 (10.50.112.0/20):

📋 Recommendations

✅ You’re Good to Go!

Optional Optimizations:

🚀 Summary

📚 Additional Resources