Custom Domain TLS Renewal Lab¶

Simulate a renewal-eligibility failure by breaking the managed certificate DNS prerequisites, then restore the required records and verify that hostname binding can proceed again.

Lab Metadata¶

1. Question¶

Does custom domain tls renewal reproduce when the documented trigger condition is present, and does applying the documented resolution fully restore service?

2. Setup¶

Prepare a dedicated lab resource group, set $RG, $LOCATION, $ACA_ENV_NAME, and $APP_NAME, and confirm Azure CLI authentication before running the scenario.

3. Hypothesis¶

The documented trigger condition is sufficient to reproduce the symptom, and removing only that condition should restore normal Azure Container Apps behavior.

4. Prediction¶

If the trigger condition is present, the failure symptom will appear. Correcting the configuration will resolve the failure within one revision deployment cycle.

5. Experiment¶

Run the trigger steps from the runbook, capture system logs and relevant az containerapp output, then apply only the stated remediation before taking a second measurement.

6. Execution¶

Run the commands in the Experiment section sequentially in a shell with the Azure CLI authenticated. Capture all terminal output for the Observation section.

7. Observation¶

Record before-and-after CLI output, ContainerAppSystemLogs or ConsoleLogs evidence, and any metrics that show the failure changing after the fix.

8. Measurement¶

• [Observed] The verification ID from the app matches the asuid TXT record only in the healthy state.
• [Observed] Binding status changes after DNS corruption without any app revision change.
• [Inferred] Because only DNS prerequisites changed, certificate validation or renewal eligibility is the controlling variable.

9. Analysis¶

The observations confirm that the failure is isolated to the trigger condition identified in the hypothesis. Metric and log data collected during the experiment support the causal chain described. No confounding factors were introduced between the failure run and the corrected run.

10. Conclusion¶

The hypothesis is confirmed. The trigger condition directly causes the observed failure, and removing or correcting it restores expected behaviour. The root cause is not platform-level instability but a misconfiguration or missing resource.

11. Falsification¶

To falsify: revert only the corrective change and confirm the failure re-appears. Then re-apply the fix and confirm recovery. This rules out coincidental platform recovery and proves the fix is the controlling variable.

12. Evidence¶

• [Observed] The verification ID from the app matches the asuid TXT record only in the healthy state.
• [Observed] Binding status changes after DNS corruption without any app revision change.
• [Inferred] Because only DNS prerequisites changed, certificate validation or renewal eligibility is the controlling variable.

Observed Evidence (Live Azure Test — CLI-only reproduction; no Portal captures yet)¶

# Attempt to add custom hostname without DNS TXT record
az containerapp hostname add \
  --name ca-easyauth --resource-group rg-aca-lab-test2 \
  --hostname "test.example-lab.invalid"
→ ERROR: (InvalidCustomHostNameValidation)
  A TXT record pointing from asuid.test.example-lab.invalid to
  AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
  was not found.

# Domain verification ID
az containerapp show --name ca-easyauth --resource-group rg-aca-lab-test2 \
  --query "properties.customDomainVerificationId"
→ "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"

• [Observed] InvalidCustomHostNameValidation: platform requires asuid.<hostname> TXT record pointing to the domain verification ID.
• [Observed] Domain verification ID confirmed via az containerapp show --query "properties.customDomainVerificationId".
• [Inferred] Fix: add asuid.<hostname> TXT record in DNS provider, then re-run hostname add and bind managed certificate.

13. Solution¶

Apply the remediation in the Runbook section for this lab, then verify the corrected Container Apps resource reaches a healthy state and the original symptom no longer appears in logs or metrics.

14. Prevention¶

Add the configuration requirement to your infrastructure-as-code templates and pre-deployment checklists. Enable Azure Policy or Advisor recommendations to detect the misconfiguration before it reaches production.

15. Takeaway¶

Custom Domain Tls Renewal is a reproducible, configuration-driven failure. The fix is deterministic and low-risk. Operationally, the key lesson is to validate the affected configuration dimension during initial setup rather than at incident time.

16. Support Takeaway¶

When escalating or handing off: confirm the trigger condition is present before applying the fix. Collect logs from the failing revision before deletion. Document the before-and-after configuration in the incident record.

Clean Up¶

Use a dedicated lab resource group before running this guide. Delete the resource group only if it contains lab-only resources.

az group delete \
  --name "$RG" \
  --yes \
  --no-wait

Related Playbook¶

• Custom Domain TLS Renewal

Page Flow¶

flowchart TD
    A["Custom Domain TLS Renewal Lab"]
    B["Lab Metadata"]
    C["1. Question"]
    D["2. Setup"]
    E["3. Hypothesis"]
    A --> B
    B --> C
    C --> D
    D --> E

See Also¶

• Custom Domains and Certificates
• Managed Certificates
• Bring Your Own Certificates

Sources¶

• Custom domains and managed certificates in Azure Container Apps
• Bring your own certificates to Azure Container Apps