How to fix IP pool is exhausted in Kubernetes

KubernetesINTERMEDIATEHIGH

IP pool exhaustion occurs when all available IP addresses in the Calico IP pool are allocated. Resolve by expanding the pool CIDR, reclaiming unused IPs, or monitoring IP usage.

What this error means

Calico manages IP address allocation for pods using IP pools. When an IP pool is exhausted, there are no more available IP addresses to assign to new pods. This prevents pod creation and stops scaling operations. The issue occurs when the CIDR range configured for the pool is too small for the number of pods needed.

Typical symptoms

How to fix "IP pool is exhausted"

1Check current IP pool status and usage

Get IP pool configuration and check available addresses:

bash

calicoctl get ippools -o yaml
calicoctl get ippool default-ipv4-ippool -o yaml | grep -A 5 "cidr|blockSize"

2Calculate IP requirements

Determine how many IPs you need:
- Max pods in cluster = nodes × pods per node
- Add buffer for growth (usually 1.5-2x expected peak)
- Account for system pods, daemonsets, statefulsets
Example: 10 nodes × 50 pods/node × 2 = 1000 IPs needed

3Create a larger IP pool

Add a new IP pool with larger CIDR range:

bash

calicoctl apply -f - << EOF
apiVersion: projectcalico.org/v3
kind: IPPool
metadata:
  name: large-pool
spec:
  cidr: 10.48.0.0/16
  blockSize: 25
EOF

Then disable the old pool and migrate pods.

4Adjust block size if using multiple pools

Reduce per-node allocation to conserve IPs:

bash

calicoctl apply -f - << EOF
apiVersion: projectcalico.org/v3
kind: IPPool
metadata:
  name: default-ipv4-ippool
spec:
  blockSize: 26  # Allocate /26 to each node (64 IPs) instead of /25 (128)
EOF

Smaller blocks = fewer wasted IPs but requires more fragmentation management.

5Disable and migrate old IP pool

Gradually migrate from old to new pool:

bash

# Disable old pool to prevent new allocation
calicoctl apply -f - << EOF
apiVersion: projectcalico.org/v3
kind: IPPool
metadata:
  name: old-pool
spec:
  disabled: true
EOF

# Delete pods to reassign from new pool
kubectl rollout restart deployment -n your-namespace

6Reclaim orphaned IP addresses

Clean up IPs not properly released:

bash

# Check IP allocation status
calicoctl ipam show

# Release stuck allocations
calicoctl ipam release --ip <orphaned-ip>

7Monitor IP pool usage over time

Set up monitoring to prevent future exhaustion:

bash

# Get current usage
calicoctl get ippool default-ipv4-ippool -o yaml | grep -E "cidr|available"

# Create Prometheus alerts
alerting_rule:
  - alert: CalicoIPPoolExhaustionWarning
    expr: calico_ippool_available_ips < 100

8Implement IP pool autoscaling strategy

For large clusters, implement automation:
1. Monitor available IPs via Prometheus
2. Create alerts at 20%, 10%, 5% available
3. Use GitOps to automatically add new pools
4. Size pools to support expected growth (2-3 years)

How to fix IP pool is exhausted in Kubernetes

What this error means

Typical symptoms

Common causes

How to fix "IP pool is exhausted"

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Official resources & further reading