The Tool Desk
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What to monitor: expiry, renewal, and deployment
1. Check the certificate in use and its expiry
Start with an inventory of the endpoints and certificates that matter, then monitor the expiration date of the certificate each endpoint actually presents. A certificate that exists in a cloud account is not necessarily the one currently served by a website or other service.
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For a third-party CA certificate used with CloudFront, AWS says to monitor its expiration date and renew or reimport it before it expires. AWS recommends doing so at least 24 hours before the current NotAfter value, then associating the replacement certificate with the distribution. AWS CloudFront certificate requirements.
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For AWS Certificate Manager (ACM), renewal status is available in the console, API, CLI, and AWS Health Dashboard. ACM documents four statuses: pending automatic renewal, pending validation, success, and failed. Pending validation means domain validation still needs to complete; failed means the certificate was not renewed before it expired. Check ACM certificate renewal status.
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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 DNS-record problems are the most likely cause when renewal fails for a DNS-validated certificate. Troubleshoot ACM certificate renewal.
3. Confirm the replacement is deployed
Renewal and deployment are separate checks. AWS documents that both are asynchronous, and several hours can pass between renewal status changes and deployment to resources. Once renewal shows success, verify the certificate presented by the endpoint rather than assuming the service switched immediately. ACM managed certificate renewal.
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Choose an AWS alerting method
For ACM certificates, the three practical choices differ in how they surface a problem. Manual views help investigate status; EventBridge routes events; CloudWatch alarms on a days-to-expiry metric.
| Method | What it provides | Coverage and limits |
|---|---|---|
| Console, API, CLI, or Health Dashboard | Visibility into ACM renewal status, including pending validation and failure. | Useful for diagnosis, but periodic manual inspection alone does not route an advance warning to the responsible team. AWS ACM documentation. |
| Amazon EventBridge | Approaching-expiration events for active ACM certificates, published daily. | Default lead windows begin 30 days before expiry for public certificates and 45 days for private and imported certificates; AWS says the timing can be changed through the ACM API. Imported certificates must be reissued and reimported before expiry. ACM’s Certificate Expired event is not available for imported certificates, so do not rely on that event as their warning path. ACM events supported by EventBridge. |
| Amazon CloudWatch | The DaysToExpiry metric reports days until expiration for each certificate and is published twice daily. |
The metric stops after expiration. Set an alarm early enough for the responsible team to investigate, complete validation, renew, and deploy. Monitor ACM certificates with CloudWatch. |
These options are complementary: use an alert route for advance notice, then check renewal state and the served certificate to determine whether action is needed. ACM’s event timing, metric cadence, and certificate coverage are AWS-specific; they should not be assumed to apply to certificates managed by other providers.
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Respond to an alert before the deadline
- Pending validation: Check the validation method and complete the required action. For DNS validation, confirm the expected CNAME records exist and are accurate; for email validation, check for the required domain-owner action.
- Renewal failed: Treat the certificate as at risk of expiry and address the reported validation or renewal issue promptly.
- Imported certificate: Arrange to reissue and reimport it before expiry. The imported-certificate limitation on the expired event makes an approaching-expiration warning especially important.
- Renewal succeeded but the endpoint still shows the old certificate: Allow for asynchronous deployment, then verify the certificate presented by the service. For CloudFront using a third-party certificate, associate the replacement with the distribution and meet AWS’s recommended 24-hour buffer before
NotAfter.
Keep ACM validity figures in context
AWS documentation history reports a 198-day validity period for public ACM certificates in 2026 and a maximum validity of 200 days for public ACM certificates issued after March 15, 2026. It also reports that ACM’s public-certificate renewal window was updated to 45 days before expiry. These figures describe AWS ACM—not a universal validity period or renewal schedule for SSL/TLS certificates. ACM public certificates.
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