Scitix Siclaw Siclaw

Resource Insufficiency Diagnosis

This guide helps diagnose resource shortage issues in Volcano-scheduled workloads. Resource insufficiency is one of the most common causes of scheduling failures.

Scope: This skill is for diagnosis only. Once you identify the root cause, report it to the user and stop. Do NOT attempt to modify resource quotas or delete workloads.

When to Use This Guide

Use this skill when:

• Events show Insufficient cpu or Insufficient memory
• Pods are stuck in Pending with resource-related events
• Nodes show zero allocatable resources
• Pods are being OOMKilled (Out of Memory)
• FailedScheduling events mention resource constraints

Types of Resource Issues

1. Cluster-Wide Resource Exhaustion

The entire cluster lacks sufficient resources to meet the workload demands.

2. Resource Fragmentation

Total resources exist but are distributed across too many nodes to satisfy specific scheduling constraints (like Gang scheduling).

3. Per-Node Resource Shortage

Individual nodes lack enough resources, even though the cluster as a whole has capacity.

4. Queue Resource Limits

The Queue has reached its deserved resource limit, preventing new pods from being scheduled.

Diagnostic Steps

Step 1: Identify Resource Shortage Type

Check the specific error message in events:

kubectl get events -n <namespace> --field-selector involvedObject.name=<pod-name> --sort-by='.lastTimestamp'

Common error patterns:

Step 2: Check Pod Resource Requests

Determine how much resources the pod is requesting:

kubectl get pod <pod-name> -n <namespace> -o jsonpath='{.spec.containers[*].resources.requests}'

For detailed breakdown:

kubectl get pod <pod-name> -n <namespace> -o yaml | grep -A 10 "resources:"

Key fields:

• resources.requests.cpu - CPU cores requested (e.g., "100m" = 0.1 core, "2" = 2 cores)
• resources.requests.memory - Memory requested (e.g., "1Gi", "512Mi")
• resources.requests.nvidia.com/gpu - GPUs requested
• resources.limits - Maximum allowed (may be different from requests)

Step 3: Check Node Allocatable Resources

View total allocatable resources per node:

kubectl get nodes -o custom-columns='NAME:.metadata.name,CPU:.status.allocatable.cpu,MEM:.status.allocatable.memory,GPU:.status.allocatable.nvidia\.com/gpu,PODS:.status.allocatable.pods'

For detailed node information:

kubectl describe node <node-name>

Key concepts:

• allocatable = Total capacity - System reserved - Kubelet reserved
• capacity = Total hardware capacity
• The difference is reserved for system/Kubernetes daemons

Step 4: Check Current Resource Usage

If metrics-server is available:

kubectl top nodes

For per-node pod usage:

kubectl top pods --all-namespaces --sort-by=cpu | head -20
kubectl top pods --all-namespaces --sort-by=memory | head -20

Note: If metrics-server is not available, you can still see resource allocation (requests) but not actual usage.

Step 5: Calculate Resource Availability

For each node, calculate available resources:

Available CPU = allocatable.cpu - sum(all pod requests on node)
Available Memory = allocatable.memory - sum(all pod requests on node)

Quick check with:

kubectl describe node <node-name> | grep -A 20 "Allocated resources"

Look for:

• cpu-requests vs cpu-capacity
• memory-requests vs memory-capacity
• Percentage of allocation (high % = resource pressure)

Step 6: Check for Resource Fragmentation

For Gang scheduling or affinity constraints, fragmentation is critical:

# Count nodes that can fit a single pod
NODE_CPU_REQ="4"
NODE_MEM_REQ="8Gi"

kubectl get nodes -o json | jq -r '
  .items[] |
  select(.status.allocatable.cpu | tonumber >= '"$NODE_CPU_REQ"') |
  select(.status.allocatable.memory | ascii_downcase | gsub("[gimk]"; "") | tonumber >= 8) |
  .metadata.name'

Fragmentation indicators:

• Many nodes with small amounts of free resources
• No single node can satisfy the pod's resource needs
• Total cluster resources sufficient but poorly distributed

Common Scenarios

Scenario 1: Pod Requests Exceed Any Single Node

Symptom: Insufficient cpu or Insufficient memory on all nodes

Diagnosis:

# Check pod request
kubectl get pod <pod> -o jsonpath='{.spec.containers[0].resources.requests.cpu}'
# Output: 32

# Check largest node's allocatable
kubectl get nodes -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.allocatable.cpu}{"\n"}{end}' | sort -k2 -n | tail -1
# Output: node-1    16

Analysis: Pod requests 32 CPUs, but largest node only has 16 allocatable.

Solution:

• Reduce pod resource requests (if actual usage is lower)
• Add larger nodes to cluster
• Use node pool with bigger instances

Scenario 2: Cluster at Capacity

Symptom: Most nodes show high allocation percentage

Diagnosis:

kubectl describe node <node-name> | grep "Allocated resources"
# cpu-requests:  14900m (93%)
# memory-requests:  55000Mi (85%)

Analysis: Nodes are 85-93% allocated, leaving little room for new pods.

Solution:

• Scale cluster (add more nodes)
• Review and optimize resource requests (may be over-provisioned)
• Consider cluster autoscaler for dynamic scaling

Scenario 3: Resource Fragmentation

Symptom: Gang scheduling fails despite total resources being sufficient

Diagnosis:

# Total cluster CPU
kubectl get nodes -o jsonpath='{range .items[*]}{.status.allocatable.cpu}{"\n"}{end}' | awk '{sum+=$1} END {print sum}'
# Output: 64

# Available nodes for 4-CPU pods
kubectl get nodes -o custom-columns='NAME:.metadata.name,CPU:.status.allocatable.cpu' | awk '$2 >= 4 {count++} END {print count " nodes can fit the pod"}'
# Output: 2 nodes can fit the pod

# But we need 8 pods for Gang
# 2 < 8, so Gang fails

Analysis: Total cluster has 64 CPUs, but only 2 nodes have 4+ CPUs. Gang needs 8 pods.

Solution:

• Enable binpack plugin to concentrate pods
• Defragment by draining and rebalancing nodes
• Use larger nodes to reduce fragmentation

Scenario 4: Queue Resource Exhaustion

Symptom: Events mention queue limits, PodGroup stays in Pending

Diagnosis:

# Check queue status
kubectl get queue <queue-name> -o yaml

Look for:

• status.allocated >= status.deserved
• state is Open but no capacity available

Analysis: Queue has used all its deserved resources.

Solution:

• Increase queue weight or capability
• Wait for other jobs to complete
• Use volcano-queue-diagnose for detailed analysis

Scenario 5: GPU Resource Shortage

Symptom: Insufficient nvidia.com/gpu in events

Diagnosis:

# Check GPU allocatable
kubectl get nodes -o custom-columns='NAME:.metadata.name,GPU:.status.allocatable.nvidia\.com/gpu'

# Check GPU usage (if metrics available)
kubectl top nodes --show-capacity 2>/dev/null || echo "GPU metrics not available"

Analysis: GPU resources are fully allocated or fragmented across nodes.

Solution:

• Verify GPU device plugin is running
• Check if GPUs are properly allocatable on nodes
• Consider GPU sharing if workload supports it

Resource Calculation Examples

Example 1: Calculate Total Cluster Capacity

kubectl get nodes -o json | jq -r '
  .items |
  map(.status.allocatable) |
  reduce .[] as $item ({}; 
    . + {cpu: ((.cpu // 0 | tonumber) + ($item.cpu | tonumber)),
         memory: ((.memory // 0) + ($item.memory | tonumber))})'

Example 2: Find Pods with High Resource Requests

kubectl get pods --all-namespaces -o json | jq -r '
  .items[] |
  select(.spec.containers[].resources.requests.cpu | tonumber > 4) |
  "\(.metadata.namespace)/\(.metadata.name): \(.spec.containers[].resources.requests)"'

Example 3: Check Resource Utilization vs Request

# High-level view
kubectl get nodes -o custom-columns='NAME:.metadata.name,CPU_ALLOC:.status.allocatable.cpu,MEM_ALLOC:.status.allocatable.memory'

Prevention and Best Practices

1. Right-size resource requests

   • Set requests based on actual usage, not maximum possible
   • Use Vertical Pod Autoscaler (VPA) for recommendations

2. Use cluster autoscaler

   • Automatically scale nodes based on pending pod demands
   • Configure appropriate node pools for different workloads

3. Enable binpack plugin

   • Reduces fragmentation by concentrating pods
   • Better for batch workloads

4. Monitor resource quotas

   • Set up alerts for queue resource exhaustion
   • Use volcano-queue-diagnose proactively

5. Regular capacity planning

   • Track resource growth trends
   • Plan cluster expansion before hitting capacity

See Also

• volcano-diagnose-pod - General Pod scheduling diagnosis
• volcano-gang-scheduling - Gang scheduling constraint issues
• volcano-queue-diagnose - Queue resource analysis
• volcano-node-resources - Node resource querying

Source: scitix/siclaw — distributed by TomeVault.