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nic-debugging

Testing & Quality
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Debugging and troubleshooting patterns for NIC. Use when diagnosing failures, tracing issues, investigating NGINX reload errors, config generation bugs, or controller sync problems.

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Source SKILL.md: https://github.com/nginx/kubernetes-ingress/blob/HEAD/.github/skills/nic-debugging/SKILL.md

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Debugging and Troubleshooting

Common Failure Modes

NGINX Reload Failure

Symptom: Controller logs show "reload failed" or NGINX returns error status.

Diagnosis:

  1. Check controller logs for the generated config that failed
  2. Look for nginx -t output in logs — shows exact syntax error and line number
  3. Common causes:
    • Unsanitized user string injected into config (missing containsDangerousChars() check)
    • Template guard missing ({{- if }} / {{- with }}) for optional field
    • Duplicate directive from conflicting policies
    • Invalid upstream when no endpoints available

Fix pattern:

  • Find the template or config generation code that produced the bad directive
  • Add validation to reject the input earlier, OR fix the template guard
  • Verify with make test — snapshot tests catch most template output issues

CRD Not Taking Effect

Symptom: User applies VirtualServer/Policy but NGINX config doesn't change.

Diagnosis:

  1. Check CRD status: kubectl get vs <name> -o yaml — look at .status.message
  2. Check controller logs for sync errors on that resource
  3. Common causes:
    • Validation rejecting the resource (check status.state: Invalid)
    • Missing secret reference (TLS, JWT, OIDC secrets)
    • Policy referenced but not found in namespace
    • Resource conflicts (duplicate host/path)

Controller Crash / Panic

Symptom: Pod restarts, panic in logs.

Diagnosis:

  1. Check logs for the panic stack trace
  2. Common causes:
    • Nil pointer on optional CRD field (forgot *bool/*int check)
    • Map access without nil check on .Spec.X field
    • Race condition in concurrent secret/config access
  3. Look for the file:line in the stack trace → usually in internal/configs/ or internal/k8s/

Snapshot Test Failure

Symptom: make test fails with snapshot mismatch.

Diagnosis:

  1. This means template output changed — could be intentional or regression
  2. Review the diff shown in test output
  3. If change is intentional: make test-update-snaps to regenerate
  4. If change is unintentional: your template edit had side effects — fix the template

Log Locations

ContextLocationWhat to look for
Controller logsPod stdout/stderrSync errors, reload status, validation failures
NGINX error log/var/log/nginx/error.log in containerConfig syntax errors, upstream failures
NGINX access log/var/log/nginx/access.log in containerRequest routing verification

Validation and Diagnostic Tools

ToolCommandPurpose
Config testnginx -t (inside container)Validate NGINX config syntax
CRD statuskubectl get vs,vsr,ts,pol -ACheck resource state
Controller logskubectl logs <pod> -n nginx-ingressRuntime errors
Describe eventskubectl describe vs <name>Kubernetes events for the resource
Generated configkubectl exec <pod> -- cat /etc/nginx/conf.d/<file>Inspect actual generated NGINX config

Debugging Workflow

  1. Reproduce — Get the exact error. Is it a reload failure? Wrong routing? Crash?
  2. Assess security impact — Before diving into the fix, ask:
    • Is this bug exploitable? (Can external input trigger it?)
    • Does the failure expose sensitive data in logs or error messages?
    • Could an attacker craft input to reach this code path?
    • If exploitable: flag for security review BEFORE fixing
  3. Locate the layer — Use logs and status to determine:
    • Validation layer? → status.state: Invalid with reason
    • Config generation? → Generated config has wrong directives
    • Template? → Snapshot test shows the issue
    • Controller? → Sync error in logs, resource not processed
  4. Isolate — Find minimum CRD/annotation that triggers the issue
  5. Fix — Make the change in the correct layer (don't fix templates for validation bugs)
  6. Verify — make test passes, snapshot output is correct
  7. Prevent — Add a test case that would catch this regression (include negative/malicious input tests if the bug was in a validation path)

Config Generation Debugging

When the generated NGINX config is wrong:

  1. Find the template struct — Which struct feeds the template? Check internal/configs/version2/http.go (VS) or internal/configs/version1/config.go (Ingress)
  2. Find the config generator — Where is the struct populated? Check internal/configs/virtualserver.go or internal/configs/ingress.go
  3. Find the template — Which .tmpl file renders it? Check internal/configs/version2/nginx-plus.virtualserver.tmpl or the OSS variant
  4. Add a snapshot test — Create a test case in the appropriate _test.go file with the input that triggers the bug, run make test-update-snaps to capture current (wrong) output, then fix and regenerate

Common Gotchas When Debugging

  • NGINX config errors show line numbers in the GENERATED file, not your template — map back manually
  • Secret-related failures often show as "file not found" in NGINX logs (secret not written to filesystem yet)
  • Policy ordering matters — first matching policy wins, check generatePolicies() logic
  • Plus-only features will work in Plus template but silently produce invalid config in OSS template
  • containsDangerousChars() failures are validation errors and typically result in status.state: Invalid — check the CRD status message and controller logs

Security-Sensitive Debugging

When debugging an issue that involves user-provided input reaching NGINX config:

  1. Trace the input path — From CRD field / annotation → validation → config struct → template → NGINX config file. Identify every point where sanitization SHOULD happen.
  2. Check for injection — Can crafted input inject NGINX directives? Look for ;, {, }, $, newlines, backticks in the user-controlled value.
  3. Verify the guard — Does containsDangerousChars() or ValidateEscapedString() cover this path? If not, the bug is a security vulnerability.
  4. Never log secrets — When debugging TLS/JWT/OIDC issues, mask credential values. Log key names and paths, not contents.
  5. Check RBAC — If the issue involves unauthorized access, verify ServiceAccount permissions and RBAC role bindings before looking at code.
, newlines, backticks in the user-controlled value.\n3. **Verify the guard** — Does `containsDangerousChars()` or `ValidateEscapedString()` cover this path? If not, the bug is a security vulnerability.\n4. **Never log secrets** — When debugging TLS/JWT/OIDC issues, mask credential values. Log key names and paths, not contents.\n5. **Check RBAC** — If the issue involves unauthorized access, verify ServiceAccount permissions and RBAC role bindings before looking at code.\n"}],"versionEndpoint":"/skill/api/version"}