In today's HTTPS-dominated website environment, SSL certificates are no longer just optional security components, but critical infrastructure directly related to user trust, search engine indexing, and business continuity. However, in actual operation and maintenance, many websites encounter the same problem after running for a period of time: SSL certificates expire. Browser pop-ups of "Insecure" and "Certificate expired" not only deter users but can also lead to decreased search rankings, failed API calls, and even affect the normal use of third-party payment and API services. Understanding why SSL certificates expire, how to properly renew them, and how to prevent similar problems from recurring is a skill every website operator must master.

　　SSL certificates themselves have a clearly defined validity period. Whether it's a free DV certificate or a paid OV or EV certificate, none are valid indefinitely. This design aims to reduce the long-term risks of key leaks and encourage sites to regularly update their encryption materials. Especially now that mainstream CAs have shortened certificate validity to one year or even 90 days, even higher requirements are placed on operational standards. Once a certificate expires, the browser will be unable to complete trust verification during the TLS handshake, resulting in blocked access or a forced warning.

　　When you discover that your website's SSL certificate has expired, the first step is not to immediately and frantically "reinstall the website," but rather to confirm the certificate type, issuing authority, and current deployment location. You can view the certificate details through your browser to confirm whether it's a main domain certificate, a wildcard certificate, or a multi-domain certificate, and check for any missing intermediate certificates. Some seemingly "expired" cases are actually due to incomplete server certificate chains causing trust failures; only after confirming expiration should you proceed with the update process.

　　When updating an SSL certificate, the core step usually begins with regenerating the CSR file. The CSR (Certificate Signing Request) contains the domain name, public key, and organization information. For most server environments, whether Nginx, Apache, or IIS, a new CSR and private key can be generated using OpenSSL or server management tools. It is crucial to ensure the private key is securely stored and not overwritten or leaked; otherwise, even if the certificate update is successful, it may introduce security vulnerabilities.

　　After generating a CSR, you need to apply for a new certificate from a Certificate Authority (CA). If you are using a free certificate service, such as a common automated certificate solution, you can complete the application and verification process directly through client tools. If you are using a commercial certificate, you need to log in to the CA management backend to submit the CSR and complete domain verification or company information review depending on the certificate type. Domain verification is the most easily overlooked yet crucial step in this process. Common methods include DNS resolution verification, file verification, or email verification. Incorrect configuration in any step will result in the certificate failing to be issued.

　　Once the new SSL certificate is successfully issued, the next step is to replace and deploy it on the server. This step requires ensuring that the new certificate correctly matches the original private key and that both the server certificate and intermediate certificates are fully installed. Taking an Nginx environment as an example, you typically need to specify the paths to the certificate file and private key file in the configuration file and confirm that the intermediate certificate has been merged or correctly referenced. After completing the configuration, reload or restart the service to make the new certificate effective. At this point, it is recommended to verify the certificate using multiple browsers and online testing tools to confirm that there are no certificate chain errors, hostname mismatches, or other issues.

　　One often overlooked detail during SSL certificate updates is the impact on business systems. Certificate updates not only affect website access but can also affect API callbacks, payment notifications, third-party API calls, and access to mini-programs and embedded WebViews within apps. If these systems have strict verification of certificate fingerprints or validity periods, testing is necessary before the update to avoid cascading failures after the certificate switch. For high-traffic sites, it is recommended to complete the certificate update during off-peak hours and prepare rollback plans in advance.

　　From a long-term operational perspective, preventing SSL certificates from expiring again is more important than "post-event remediation." Establishing a certificate validity monitoring mechanism is one of the most effective ways to mitigate risk. A monitoring platform can periodically check the remaining validity days of certificates and automatically send alerts when expiration is approaching. For sites using automated certificates, enable automatic renewal and regularly check renewal logs to ensure the process is genuinely effective, rather than just appearing "configured." Furthermore, properly planning certificate types and use cases also helps reduce management complexity. For example, if multiple subsites are deployed on the same server or within the same business system, using wildcard certificates can reduce the number of certificates; multi-domain certificates are suitable for projects requiring centralized management. The fewer certificates, the lower the probability of operational errors. Of course, such choices require a balance between security, cost, and management efficiency.

　　Website SSL certificate expiration is not a complex but "low-frequency" issue, but rather a daily matter highly dependent on operational standards and process management. Only by addressing it from multiple perspectives, including update processes, deployment details, business linkages, and long-term monitoring, can we truly solve current problems while avoiding future risks. Treating certificate management as part of the website infrastructure, rather than a temporary task, is key to ensuring the long-term secure and stable operation of the website.

　　FAQs:

　　Q1: Is website data still secure after an SSL certificate expires?

　　A1: Certificate expiration itself does not mean data has been leaked, but the browser cannot verify the server's identity, communication loses its trust guarantee, and there is a risk of man-in-the-middle attacks.

　　Q2: Will the original HTTPS links become invalid after the certificate is updated?

　　A2: No. As long as the domain name remains unchanged and the configuration is correct, the existing HTTPS link will remain valid, and users will hardly notice the certificate replacement process.

　　Q3: Is there a difference between the update methods for free and paid SSL certificates?

　　A3: The update process is technically similar; the main difference lies in the verification method and validity period. Free certificates typically have shorter validity periods and rely more on automated renewal mechanisms.

　　Q4: What are the most common reasons for certificate update failures?

　　A4: Common reasons include CSR and private key mismatch, domain name verification failure, missing intermediate certificates, and incorrect server reload configuration.

　　Q5: Can multiple SSL certificates be installed on one server simultaneously?

　　A5: Yes. Through SNI technology, different SSL certificates can be deployed for multiple domains on the same IP address and the same server without conflict.