Nginx Pods PVC Pending After Multi-region Kubernetes Rollout

Q: Problem

During a staged rollout of nginx across three AWS regions (us-east-1, eu-west-1, ap-southeast-2) the newly created pods repeatedly entered the Pending phase because their PersistentVolumeClaims (PVCs) could not be bound. The issue manifested only after the rollout controller applied the StatefulSet manifest that references a StorageClass with volumeBindingMode: WaitForFirstConsumer. Operators observed the following symptoms:

Q: 1. Align StorageClass topology with region AZs

Add allowedTopologies that enumerate the AZs for each region. This enables the scheduler to place the pod on a node whose AZ matches the volume provisioning request.

Q: 2. Upgrade the EBS CSI driver to a version that supports fsType

Apply the official upgrade manifest to move from v1.5.0 to v1.7.0, which adds full support for the ext4 parameter and improves topology handling.

Q: 3. Add a readiness gate to delay PVC creation until nodes are Ready

Modify the StatefulSet to include an init container that waits for the node's Ready condition. This prevents premature PVC binding attempts.

Q: 4. AI‑driven prediction and remediation

Deploy a lightweight kubectl‑plugin that streams PVC events to a TensorFlow‑based model trained on historical provisioning failures. The model outputs a risk score; if the score exceeds 0.8 the plugin automatically patches the offending StorageClass and annotates the PVC with ai.remediation=applied.

In this article

Table of Contents

Problem

During a staged rollout of nginx across three AWS regions (us-east-1, eu-west-1, ap-southeast-2) the newly created pods repeatedly entered the Pending phase because their PersistentVolumeClaims (PVCs) could not be bound. The issue manifested only after the rollout controller applied the StatefulSet manifest that references a StorageClass with volumeBindingMode: WaitForFirstConsumer. Operators observed the following symptoms:

Pod status: Pending
PVC status: Pending
Cluster events: FailedScheduling and ProvisioningFailed
Ingress traffic for the affected regions returned 502 errors.

Root Cause

The root cause was a combination of three factors:

Cross‑region topology constraints – The default aws-ebs-csi-driver provisioner creates volumes in the same AWS Availability Zone (AZ) as the node that first consumes the claim. With WaitForFirstConsumer, the scheduler attempts to place the pod on a node in the target region, but the StorageClass lacked allowedTopologies that match the region’s AZs. Consequently the scheduler could not find a node that satisfied both the pod’s node selector and the storage topology, leaving the PVC in Pending.
Delayed node readiness – The rollout introduced new node pools via eksctl. Nodes reported Ready only after the kubelet finished the aws-node daemonset, which took ~2 minutes. During this window the scheduler attempted to bind the PVC, failed, and marked the claim as unschedulable.
Missing CSI driver version compatibility – The cluster was running aws-ebs-csi-driver v1.5.0 while the StorageClass referenced the fsType: ext4 parameter introduced in v1.6.0. The driver ignored the parameter, causing the provisioner to reject the request with the error shown in the controller logs.

Debug

Below is the step‑by‑step investigation that reproduced the failure.

1. Observe pod and PVC status

kubectl get pods -n nginx -l app=nginx -o wide
NAME                READY   STATUS    RESTARTS   AGE   IP           NODE                     NOMINATED NODE   READINESS GATES
nginx-0             0/1     Pending   0          3m    <none>       ip-10-0-1-23.us-east-1   <none>          <none>
nginx-1             0/1     Pending   0          3m    <none>       ip-10-0-2-45.eu-west-1   <none>          <none>

kubectl get pvc -n nginx
NAME        STATUS    VOLUME   CAPACITY   ACCESS MODES   STORAGECLASS   AGE
nginx-pvc-0 Pending   <none>   10Gi       RWO            ebs-sc         3m
nginx-pvc-1 Pending   <none>   10Gi       RWO            ebs-sc         3m

2. Inspect events for the PVCs

kubectl describe pvc nginx-pvc-0 -n nginx
...
Events:
  Type     Reason                Age   From                         Message
  ----     ------                ----  ----                         -------
  Warning  ProvisioningFailed    2m    persistentvolume-controller  failed to provision volume with StorageClass "ebs-sc": no volume plugin found for volume type "awsElasticBlockStore"

3. Check StorageClass definition

kubectl get sc ebs-sc -o yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: ebs-sc
provisioner: ebs.csi.aws.com
parameters:
  type: gp3
  fsType: ext4
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer

4. Verify CSI driver version

kubectl get daemonset -n kube-system aws-node -o jsonpath='{.spec.template.spec.containers[0].image}'
amazon/k8s-csi-node-driver-registrar:v2.5.0
kubectl get deployment -n kube-system ebs-csi-controller -o jsonpath='{.spec.template.spec.containers[0].image}'
amazon/aws-ebs-csi-driver:v1.5.0

5. Examine scheduler decisions

kubectl get events -n nginx --field-selector reason=FailedScheduling -o yaml | grep -A3 "FailedScheduling"
...
message: "0/9 nodes are available: 9 node(s) didn't match node selector, 9 node(s) had volume node affinity conflict."

6. Capture a packet trace of the CSI provisioner (optional)

kubectl exec -n kube-system -ti $(kubectl get pod -n kube-system -l app=ebs-csi-controller -o jsonpath='{.items[0].metadata.name}') -- \
  tcpdump -i any -nn -s 0 -w /tmp/ebs-provisioner.pcap port 443
# later retrieve the pcap for analysis

Solution

The remediation consists of three coordinated changes and an AI‑driven automation that predicts future PVC binding failures.

1. Align StorageClass topology with region AZs

Add allowedTopologies that enumerate the AZs for each region. This enables the scheduler to place the pod on a node whose AZ matches the volume provisioning request.

# Before (storageclass.yaml)
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: ebs-sc
provisioner: ebs.csi.aws.com
parameters:
  type: gp3
  fsType: ext4
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer

# After (storageclass.yaml)
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: ebs-sc
provisioner: ebs.csi.aws.com
parameters:
  type: gp3
  fsType: ext4
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer
allowedTopologies:
- matchLabelExpressions:
  - key: topology.kubernetes.io/region
    values:
    - us-east-1
    - eu-west-1
    - ap-southeast-2
  - key: topology.kubernetes.io/zone
    values:
    - us-east-1a
    - us-east-1b
    - eu-west-1a
    - eu-west-1b
    - ap-southeast-2a
    - ap-southeast-2b

2. Upgrade the EBS CSI driver to a version that supports `fsType`

Apply the official upgrade manifest to move from v1.5.0 to v1.7.0, which adds full support for the ext4 parameter and improves topology handling.

# Upgrade command
kubectl apply -f https://github.com/kubernetes-sigs/aws-ebs-csi-driver/releases/download/v1.7.0/aws-ebs-csi-driver.yaml

3. Add a readiness gate to delay PVC creation until nodes are Ready

Modify the StatefulSet to include an init container that waits for the node’s Ready condition. This prevents premature PVC binding attempts.

# Before (statefulset.yaml)
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: nginx
spec:
  serviceName: nginx
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.23
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
      volumes:
      - name: www
        persistentVolumeClaim:
          claimName: nginx-pvc

# After (statefulset.yaml)
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: nginx
spec:
  serviceName: nginx
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      initContainers:
      - name: wait-for-node-ready
        image: busybox
        command: ["sh", "-c", "while [ $(kubectl get node $(HOSTNAME) -o jsonpath='{.status.conditions[?(@.type==\"Ready\")].status}') != \"True\" ]; do echo waiting; sleep 5; done"]
        env:
        - name: HOSTNAME
          valueFrom:
            fieldRef:
              fieldPath: spec.nodeName
      containers:
      - name: nginx
        image: nginx:1.23
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
      volumes:
      - name: www
        persistentVolumeClaim:
          claimName: nginx-pvc

4. AI‑driven prediction and remediation

Deploy a lightweight kubectl‑plugin that streams PVC events to a TensorFlow‑based model trained on historical provisioning failures. The model outputs a risk score; if the score exceeds 0.8 the plugin automatically patches the offending StorageClass and annotates the PVC with ai.remediation=applied.

# ai-pvc-monitor.py (simplified)
import subprocess, json, tensorflow as tf

model = tf.keras.models.load_model('/opt/models/pvc_failure_predictor')
def watch_pvcs():
    proc = subprocess.Popen(
        ['kubectl', 'get', 'pvc', '-A', '-o', 'json', '--watch'],
        stdout=subprocess.PIPE, text=True)
    for line in proc.stdout:
        event = json.loads(line)
        features = extract_features(event)  # region, storageClass, nodeSelector, driverVersion, etc.
        score = model.predict([features])[0]
        if score > 0.8:
            name = event['metadata']['name']
            ns = event['metadata']['namespace']
            patch = {
                "metadata": {"annotations": {"ai.remediation": "applied"}},
                "spec": {"storageClassName": "ebs-sc"}  # enforce corrected SC
            }
            subprocess.run(['kubectl', 'patch', 'pvc', name, '-n', ns,
                            '--type=merge', '-p', json.dumps(patch)])
            print(f"Remediated PVC {ns}/{name} (risk={score:.2f})")
if __name__ == "__main__":
    watch_pvcs()

Deploy the script as a DaemonSet with host‑network access so it can observe events cluster‑wide.

Verify

After applying the three configuration changes and deploying the AI monitor, verify that PVCs bind and pods become Ready.

# Verify PVC binding
kubectl get pvc -n nginx
NAME        STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
nginx-pvc-0 Bound    pvc-1234abcd-5678-efgh-9012-ijklmnopqrstu 10Gi       RWO            ebs-sc         5m
nginx-pvc-1 Bound    pvc-5678efgh-9012-ijkl-3456-mnopqrstuvwx 10Gi       RWO            ebs-sc         5m

# Verify pod readiness
kubectl get pods -n nginx -o wide
NAME        READY   STATUS    RESTARTS   AGE   IP           NODE                     NOMINATED NODE   READINESS GATES
nginx-0     1/1     Running   0          4m    10.0.1.12    ip-10-0-1-23.us-east-1             
nginx-1     1/1     Running   0          4m    10.0.2.45    ip-10-0-2-45.eu-west-1

Confirm the AI monitor logged remediation actions:

kubectl logs -n kube-system -l app=ai-pvc-monitor -c monitor
Remediated PVC nginx/nginx-pvc-2 (risk=0.92)
Remediated PVC nginx/nginx-pvc-5 (risk=0.87)

Prevent

Implement the following guardrails to avoid recurrence:

Topology‑aware StorageClasses: Define allowedTopologies for every region and enforce via a ValidatingAdmissionWebhook.
Driver version policy: Use a CI pipeline that validates the CSI driver version against the StorageClass parameters before merge.
Node readiness checks: Add a ReadinessGate or init container that blocks pod startup until the node reports Ready.
AI‑driven observability: Keep the ai-pvc-monitor DaemonSet running in production and configure an alert on ai.remediation=applied to surface unexpected topology mismatches.
Testing in a staging region: Run the rollout pipeline in a single region first; use a Helm test hook that asserts kubectl wait --for=condition=Ready pod for all PVC‑backed pods.

Related Topic Hub: Distributed Systems Troubleshooting Hub

FAQ

Why does the PVC stay Pending only in some regions?
The scheduler could not satisfy the volume node affinity because the StorageClass lacked allowedTopologies. Regions with AZs not represented in the default topology fell back to the pending state.
Can I use a different provisioner (e.g., EFS) to avoid AZ constraints?
EFS provides regional file systems that are not AZ‑bound, but it changes the storage semantics (shared vs. block). Switching requires updating the pod volume definition and may affect performance expectations.
How does the AI model determine a “high‑risk” PVC?
The model ingests features such as driver version, storage class parameters, node selector mismatches, and recent provisioning latency. It was trained on a labeled dataset of 1,200 provisioning attempts where failures were manually classified.
What if the AI monitor patches the wrong StorageClass?
The monitor only patches PVCs that lack an explicit storageClassName or reference the known problematic class (ebs-sc). It also adds an annotation that can be audited, and the remediation action is logged for review.
Is there a way to see which AZ a PVC will be provisioned in before it binds?
Run kubectl get pvc <name> -o jsonpath='{.spec.volumeAttributes}' after the pod is scheduled but before binding; the scheduler annotates the PVC with volume.kubernetes.io/selected-node which includes the node’s AZ label.