Istio Sidecar Injection Not Working: How to Fix Envoy Proxy Injection Failures
Fix Istio sidecar injection not working by verifying namespace labels, MutatingAdmissionWebhook configurations, and APIServer to Istiod connectivity. Complete g
- Verify the target namespace is properly labeled with istio-injection=enabled or uses the new istio.io/rev revision labels.
- Ensure that the Istio MutatingAdmissionWebhook is healthy and the Kubernetes API server can reach the istiod service over port 443.
- Check for conflicting pod-level annotations such as sidecar.istio.io/inject: "false" overriding namespace settings.
- Remember that sidecars are only injected during pod creation; you must restart existing pods for the proxy to be attached.
| Method | When to Use | Time | Risk |
|---|---|---|---|
| Namespace Labeling | When missing global injection for an entire namespace | 1 min | Low |
| Pod Annotations | To override namespace defaults on a per-deployment basis | 2 mins | Low |
| Webhook Verification | When istio injection enabled not working despite correct labels | 10 mins | Medium |
| Firewall / EKS SG Update | API Server getting timeout/context deadline exceeded reaching Istiod | 15 mins | High |
Understanding the Error: Why is Istio Sidecar Injection Not Working?
Istio's architecture relies heavily on the Envoy proxy, deployed as a sidecar container alongside your application workloads. When you encounter a scenario where istio sidecar injection not working is the primary symptom, it means the Kubernetes pod is starting up without the istio-proxy container, leaving it isolated from the service mesh. This breaks mTLS, routing, observability, and authorization policies.
Istio achieves sidecar injection using a Kubernetes feature called a MutatingAdmissionWebhook. When a new pod is submitted to the Kubernetes API server, the API server checks its webhook configurations. If the pod matches the webhook's criteria (e.g., specific namespace labels), the API server pauses the pod creation and sends a request to the istiod control plane. istiod then "mutates" the pod specification by injecting the istio-proxy container and the istio-init container (or CNI configuration), and sends the modified spec back to the API server to be scheduled.
When istio injection not working occurs, this chain is breaking down at one of several critical junctures. Below is the comprehensive, step-by-step troubleshooting guide to diagnose and resolve these injection failures.
Step 1: Verify Namespace Labels and Pod Restart Status
The most common reason engineers find istio injection enabled not working is a fundamental misunderstanding of pod lifecycle or simple mislabeling. Istio injection is triggered only upon pod creation.
First, verify that your namespace actually has the correct label. In older Istio versions (and still supported), this is istio-injection=enabled. In newer, revision-based deployments, it might be istio.io/rev=1-18-0.
Run the following command to check your namespaces:
kubectl get namespace -L istio-injection,istio.io/rev
If the label is missing, apply it:
kubectl label namespace <your-namespace> istio-injection=enabled
Crucial Caveat: If you label a namespace after pods have already been deployed, those existing pods will not automatically receive the sidecar. The webhook only intercepts API requests for new pods. You must explicitly restart the workloads to trigger injection:
kubectl rollout restart deployment <your-deployment> -n <your-namespace>
Step 2: Check for Conflicting Pod-Level Annotations
Istio evaluates injection configuration hierarchically. Even if a namespace has istio-injection=enabled, a developer might have disabled it at the deployment/pod level. Look at the template.metadata.annotations in your Deployment manifest.
If you see sidecar.istio.io/inject: "false", Istio will deliberately skip this pod.
Conversely, if your namespace is not labeled, but you want to inject a specific pod, you can use sidecar.istio.io/inject: "true". Check the applied configuration:
kubectl get deployment <deployment-name> -n <namespace> -o yaml | grep sidecar.istio.io
Additionally, Istio ignores pods that run in the host network (hostNetwork: true) by default, as injecting sidecars into the host network space introduces severe security and routing complexities.
Step 3: Investigate the MutatingAdmissionWebhook
If the labels and annotations are correct but pods are still starting without sidecars, the next step is to verify the MutatingWebhookConfiguration.
Check if the webhook exists:
kubectl get mutatingwebhookconfigurations
You should see something like istio-sidecar-injector. Inspect it:
kubectl get mutatingwebhookconfiguration istio-sidecar-injector -o yaml
Look at the namespaceSelector section. This determines which namespaces the API server will send to the webhook. Ensure your namespace labels match these selectors.
Also, check the failurePolicy. If it is set to Ignore, any network failure between the Kubernetes API server and istiod will silently fail the injection process, allowing the pod to start without the sidecar. If set to Fail, pod creation will be blocked entirely if istiod is unreachable, giving you an explicit error message like Internal error occurred: failed calling webhook....
Step 4: Network Connectivity between APIServer and Istiod (EKS/GKE Specifics)
One of the most notoriously difficult causes of istio sidecar injection not working happens on managed Kubernetes clusters like AWS EKS or GCP GKE (specifically private clusters).
The Kubernetes API server runs in a cloud-provider-managed VPC, while your istiod pods run in the worker node VPC. For the webhook to work, the API server must be able to reach the istiod service over HTTPS (port 443), which maps to port 15017 on the istiod pod.
If you check the API server logs or the replica set events (kubectl describe rs <name>) and see:
Error creating: Internal error occurred: failed calling webhook "namespace.sidecar-injector.istio.io": Post "https://istiod.istio-system.svc:443/inject?timeout=10s": context deadline exceeded
This is a guaranteed firewall or Security Group issue.
- On AWS EKS: You must ensure the Control Plane Security Group allows outbound traffic to the Worker Node Security Group on port 15017, OR the Worker Node SG allows inbound from the Control Plane SG on 15017.
- On GKE Private Clusters: You must add a firewall rule allowing the master IP range to access the worker nodes on TCP port 15017.
Step 5: Check Istiod Health and Logs
If the API server can reach istiod, but injection is still failing, the issue might be within the control plane itself. Check the status of the istiod pods:
kubectl get pods -n istio-system -l app=istiod
If they are crashing or out of memory (OOMKilled), the webhook will fail. Fetch the logs to look for injection errors:
kubectl logs -n istio-system -l app=istiod | grep -i inject
You might find errors indicating that the requested pod spec is invalid, or that istiod lacks the necessary RBAC permissions to read certain cluster resources.
Step 6: Istio CNI and Init Container Race Conditions
Finally, if the sidecar is being injected, but the pod fails to start (e.g., stuck in Init:CrashLoopBackOff), you might be facing an istio-init or Istio CNI issue.
By default, Istio injects an init container (istio-init) that requires NET_ADMIN and NET_RAW capabilities to manipulate iptables rules. If your cluster employs strict Pod Security Standards (PSS) or Pod Security Policies (PSP) that forbid elevated privileges, the init container will crash.
The modern solution to this is using the Istio CNI plugin. This moves the iptables manipulation out of the pod and into a node-level DaemonSet. However, if the istio-cni-node pods are down, or if there is a race condition where the application pod starts before the CNI plugin has configured the network, the sidecar will fail to intercept traffic. Ensure your CNI configuration is healthy and that istio-cni is correctly installed in your cluster's CNI bin directory.
Frequently Asked Questions
# 1. Check if the namespace has the correct injection labels
kubectl get namespace -L istio-injection,istio.io/rev
# 2. Label the namespace to enable injection
kubectl label namespace my-app-namespace istio-injection=enabled
# 3. Restart existing deployments to trigger the injection webhook for new pods
kubectl rollout restart deployment my-app -n my-app-namespace
# 4. Verify the sidecar proxy was injected (look for 2/2 containers ready)
kubectl get pods -n my-app-namespace
# 5. Check the MutatingWebhookConfiguration if injection still fails
kubectl get mutatingwebhookconfiguration istio-sidecar-injector -o yaml
# 6. Check Istiod logs for webhook interception errors
kubectl logs -n istio-system -l app=istiod | grep -i "inject"
# 7. Check for pod-level overriding annotations
kubectl get pod <pod-name> -n my-app-namespace -o jsonpath='{.metadata.annotations}' | grep sidecar.istio.ioError Medic Editorial
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