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To avoid an SSL/TLS certificate outage, alert on its expiration date, check whether renewal and validation succeeded, and verify that the renewed certificate is actually deployed to the endpoint. An expiration warning alone cannot confirm that renewal completed—or that users are being served the replacement certificate.
The three checks behind a useful certificate alert
1. Monitor the certificate the service actually presents
Start with an inventory of the endpoints and certificates you rely on, then monitor the expiration date of the certificate associated with each endpoint. A certificate can be renewed successfully without the replacement reaching the service that terminates TLS, so monitoring only the certificate record may miss an operational problem.
2. Track renewal and validation status
For AWS Certificate Manager (ACM), renewal status is available in the ACM console, API, CLI, and AWS Health Dashboard. ACM documents four states: pending automatic renewal, pending validation, success, and failed. Pending validation means domain validation must be completed or corrected; failed means ACM did not renew the certificate before it expired. See AWS’s ACM renewal-status guidance.
Validation depends on the method used. DNS validation can be blocked by missing or inaccurate CNAME records; email validation requires action from a domain owner; HTTP validation depends on the required validation configuration. AWS says that a DNS-validated certificate’s renewal failure is most likely caused by missing or inaccurate CNAME records. Check the relevant records and instructions in ACM’s renewal documentation and DNS validation for renewal.
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3. Confirm deployment to the endpoint
After renewal reports success, verify that the service is presenting the replacement certificate. AWS documents that renewal and deployment are asynchronous; several hours can pass between renewal status changes and deployment to resources. Treat a successful renewal and a successfully updated endpoint as separate checks. See ACM managed renewal.
Choose an AWS alert path
For ACM certificates, AWS offers event-driven warnings, a days-to-expiry metric, and status views for diagnosis. These options report different things; none should be treated as proof that a renewed certificate is live on an endpoint.
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| Method | What it tells you | Coverage and timing |
|---|---|---|
| EventBridge | An approaching-expiration event for an active certificate. | ACM’s documented default warning begins 30 days before expiry for public certificates and 45 days before expiry for private and imported certificates. Events are sent daily, and AWS says the timing can be changed through the ACM API. Imported certificates must be reissued and reimported before expiry; the ACM Certificate Expired event is unavailable for imported certificates. AWS event documentation. |
| CloudWatch | The DaysToExpiry metric reports days remaining for each certificate. |
Published twice daily; publication stops after expiration. Set an alarm threshold that gives the responsible team time to investigate, validate, renew, and deploy. AWS ACM metrics documentation. |
| Console, API, CLI, or Health Dashboard | Renewal status, including pending validation and failure. | Useful for investigating an alert or checking a certificate’s state. Manual inspection alone does not provide a routed advance warning. AWS ACM renewal-status guidance. |
Build the warning around the certificate type
ACM-issued certificates
Route EventBridge expiration events or create a CloudWatch alarm for DaysToExpiry, then investigate renewal status when a warning arrives. AWS’s documented lead times and metric cadence apply to ACM, not to every certificate authority or monitoring service.
Imported certificates
Plan to obtain a replacement from the issuing authority and import it into ACM before expiration. Do not rely on ACM’s Certificate Expired event as the warning for an imported certificate: AWS says that event is not available for imported certificates. The approaching-expiration event is the relevant documented ACM signal; see the EventBridge event details.
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Third-party certificates used with CloudFront
AWS advises monitoring the expiration date of third-party certificates used with CloudFront and renewing or reimporting them at least 24 hours before the current NotAfter value. After replacement, associate the new certificate with the distribution. See AWS’s CloudFront certificate guidance.
What the expiration figures mean for ACM
Certificate lifetimes are not universal. AWS documentation history reports 198 days for public ACM certificate validity in 2026, and a maximum validity of 200 days for public ACM certificates issued after March 15, 2026. It also records an ACM public-certificate renewal window updated to 45 days before expiry. These figures describe AWS ACM’s public certificates, not certificates from all providers. Check the applicable ACM documentation for current terms: ACM certificate characteristics.
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Respond to an alert before the deadline
- Validation is pending: Identify the validation method and complete the required action. For DNS validation, confirm the expected CNAME records are present and accurate; for email validation, check that a domain owner can act on the request.
- Renewal failed: Check the ACM status details and resolve the validation or renewal problem while the existing certificate is still valid.
- Renewal succeeded, but the endpoint still shows the old certificate: Allow for asynchronous deployment, then verify the certificate served by the affected resource rather than relying only on ACM’s status.
- The certificate was imported: Arrange reissue and reimport before expiry, and route the approaching-expiration warning rather than waiting for an expired event.
- A CloudFront third-party certificate is near expiry: Renew or reimport it at least 24 hours before its current
NotAftervalue, then associate the replacement with the distribution.
Scope of these recommendations
The alert timings, metric cadence, and event limitations described here are AWS-specific. The three-check approach—expiry, renewal and validation, and deployment—is an operational way to combine AWS’s separate monitoring and renewal guidance, not a universal framework prescribed for every certificate provider.
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