Setting Up SSL Certificate Expiry Monitoring

An expired SSL certificate is not just a technical glitch — it's a full-blown outage. The site becomes inaccessible: browsers display 'Your connection is not private', SEO rankings drop, and customer trust evaporates. One of our clients lost 150,000 rubles in a single day of downtime because their certificate expired and Let's Encrypt auto-renewal failed due to a DNS error. Monitoring certificate expiry is one of the simplest yet most effective tasks with high impact on availability. Setup takes from 30 minutes to one day and prevents catastrophic consequences.

Why track SSL certificates?

Even if you use automatic renewal via Let's Encrypt, the automation sometimes breaks. Causes: DNS errors, ACME server unreachability, write permission issues. If you don't monitor, you'll only find out from users. In a commercial environment, every hour of downtime means direct losses. We set up monitoring that alerts the team 30, 14, 7, and 1 day before expiry.

Which certificates should be monitored?

• Primary domain (example.com)
• All subdomains (if not using wildcard *.example.com)
• Intermediate certificates in the CA chain — their expiry is equally critical
• Certificates for internal services: APIs, admin panels, DevOps tools

Setting up SSL monitoring in one day

We use a combination of methods: Prometheus + Blackbox Exporter for open-source stacks, Python scripts for custom scenarios, and Uptime Robot for redundancy.

Prometheus Blackbox Exporter

# blackbox.yml
modules:
  https_check:
    prober: http
    timeout: 15s
    http:
      valid_status_codes: []
      method: HEAD
      tls_config:
        insecure_skip_verify: false
      fail_if_ssl: false
      fail_if_not_ssl: true

# prometheus.yml scrape config
scrape_configs:
  - job_name: 'ssl_certificate_check'
    metrics_path: /probe
    params:
      module: [https_check]
    static_configs:
      - targets:
          - https://example.com
          - https://api.example.com
          - https://admin.example.com
    relabel_configs:
      - source_labels: [__address__]
        target_label: __param_target
      - source_labels: [__param_target]
        target_label: instance
      - target_label: __address__
        replacement: blackbox-exporter:9115

Alert in Prometheus:

- alert: SSLCertificateExpiringSoon
  expr: probe_ssl_earliest_cert_expiry - time() < 30 * 24 * 3600
  labels:
    severity: warning
  annotations:
    summary: "SSL cert on {{ $labels.instance }} expires in {{ $value | humanizeDuration }}"

- alert: SSLCertificateExpiryCritical
  expr: probe_ssl_earliest_cert_expiry - time() < 7 * 24 * 3600
  labels:
    severity: critical
  annotations:
    summary: "SSL cert on {{ $labels.instance }} expires in {{ $value | humanizeDuration }}!"

Python script for monitoring

import ssl
import socket
from datetime import datetime, timezone

def check_ssl_expiry(hostname: str, port: int = 443) -> dict:
    context = ssl.create_default_context()
    with socket.create_connection((hostname, port), timeout=10) as sock:
        with context.wrap_socket(sock, server_hostname=hostname) as ssock:
            cert = ssock.getpeercert()
    expiry_str = cert['notAfter']
    expiry_date = datetime.strptime(expiry_str, '%b %d %H:%M:%S %Y %Z')
    expiry_date = expiry_date.replace(tzinfo=timezone.utc)
    days_remaining = (expiry_date - datetime.now(timezone.utc)).days
    return {
        'hostname': hostname,
        'expires_at': expiry_date.isoformat(),
        'days_remaining': days_remaining,
        'issuer': dict(x[0] for x in cert['issuer']),
        'subject': dict(x[0] for x in cert['subject'])
    }

The script is easy to run on a schedule via cron or AWS Lambda. We use it for services that shouldn't be exposed to the internet.

External services: Uptime Robot, Better Uptime

The simplest option — external services. Uptime Robot (free plan) checks SSL and sends notifications 30, 7, and 1 day before expiry. Better Uptime and StatusCake work similarly. Setup takes 30 minutes. It's a great complement to Prometheus monitoring for redundancy.

Comparison of methods and alert thresholds

Alert thresholds:

Common mistakes in SSL monitoring setup

• Ignoring wildcard certificates: if you use *.example.com and subdomains are added dynamically, monitor each one.
• Checking only port 443: the certificate might be valid on 443 but not on 8443.
• No alerts for intermediate certificates: expiration of a CA certificate is equally critical.
• Too infrequent checks: once a week is not enough; once daily is better.

Automating renewal with Certbot and ACM

If you use Let's Encrypt + Certbot, manual renewal isn't needed. But monitoring is still necessary — automation sometimes fails.

# Check certbot timer status
systemctl status certbot.timer

# Dry run without actual renewal
certbot renew --dry-run

Certbot renews certificates when less than 30 days remain. Monitoring triggers at < 30 days — meaning automation didn't fire in time.

For certificates managed via AWS Certificate Manager, you can set up a CloudWatch Alarm on the DaysToExpiry metric. More details in the AWS documentation.

How to choose a monitoring method?

If you already have a Prometheus stack — Blackbox Exporter gives maximum customization. When you need to quickly check a couple of domains — a Python script will suffice. For redundancy or if you lack access to internal infrastructure — an external service. We help you select the optimal option during a free consultation.

What the setup process includes

When you order the 'SSL monitoring setup' service, we perform:

• Audit of current certificates and trust chains
• Selection of the optimal tool (Prometheus/Python/external service) for your stack
• Deployment and configuration of monitoring (with code in repository)
• Alert setup with specified channels (email, Telegram, Slack)
• Documentation of the process and access transfer
• Post-launch support

Setup timelines

• Blackbox Exporter + Prometheus alerts — 0.5-1 day
• Python script + scheduled lambda/cron — 0.5 day
• External service (Uptime Robot) — 30 minutes

Timelines vary depending on the number of monitored domains and infrastructure complexity. We evaluate the project for free and provide an accurate estimate.

We have years of experience with monitoring and have set up SSL alerts for 50+ projects of varying scale — from landing pages to high-load SaaS. Contact us for a free assessment of your infrastructure. Order SSL monitoring setup and forget about certificate issues.

SSL/TLS on Wikipedia

Web Application Security: HTTPS, CSP, XSS, CSRF, WAF, DDoS Protection

A website breach rarely looks like in movies. More often it's: a bot finds an unprotected /admin/export endpoint, downloads the customer database, and closes the connection. Or: through an outdated WordPress plugin, a web shell is uploaded, and the server starts sending spam. Or quieter: an XSS in a comment field allows stealing admin session cookies, unnoticed for months. We have analyzed dozens of such cases — each vulnerability could have been fixed at the development or audit stage.

Web application security is not a single setting. It's layers of protection, each closing a separate class of attacks. Order an audit — we'll assess the project and deliver a turnkey plan within 2–4 weeks.

How do we ensure comprehensive web application security?

HTTPS and Proper TLS Configuration

HTTPS is the minimum mandatory level. But having an SSL certificate and having a properly configured TLS are different things.

In Nginx/Apache configuration we check:

• Protocols: only TLS 1.2 and TLS 1.3, SSLv3 and TLS 1.0/1.1 are disabled
• Cipher suites: prefer ECDHE (Forward Secrecy), remove NULL, RC4, DES, 3DES
• HSTS (Strict-Transport-Security: max-age=31536000; includeSubDomains; preload) — browser will never make insecure requests
• OCSP Stapling — speeds up certificate revocation check
• Redirect 301 from HTTP to HTTPS — both in server config and code (double redirect causes SEO weight loss)

Check: SSL Labs (ssllabs.com/ssltest) should show A or A+. If B, the configuration is weak.

Let's Encrypt + Certbot for production is standard. Automatic renewal via certbot renew in cron. Wildcard certificates for subdomains via DNS-01 challenge.

Content Security Policy: The Most Powerful and Complex Protection

CSP is an HTTP header that tells the browser which sources are allowed to load resources. A properly configured CSP completely blocks most XSS attacks, even if the vulnerability exists in the code.

The problem: breaking the site with an incorrect CSP is easy. default-src 'none' — and fonts, images, JS stop working. So we start with Content-Security-Policy-Report-Only — CSP logs violations but does not block anything. We monitor reports for 2–4 weeks, refine the policy, then switch to enforcement mode.

Example of a real policy for a site with Google Analytics, Google Fonts, and Stripe:

Content-Security-Policy:
  default-src 'self';
  script-src 'self' https://www.googletagmanager.com https://js.stripe.com 'nonce-{random}';
  style-src 'self' https://fonts.googleapis.com 'unsafe-inline';
  font-src 'self' https://fonts.gstatic.com;
  frame-src https://js.stripe.com;
  img-src 'self' data: https://www.google-analytics.com;
  connect-src 'self' https://api.stripe.com https://www.google-analytics.com;
  report-uri /csp-report;

nonce — a random string generated server-side per request. Inline scripts with the correct nonce are allowed; without nonce, they are blocked. This completely breaks XSS via <script>alert(1)</script>.

'unsafe-inline' in style-src is a compromise for inline styles. It's better to remove it by moving all styles to CSS files, but that requires refactoring.

Why XSS Remains the Most Common Vulnerability?

XSS (Cross-Site Scripting) — injection of JS code through user input. According to OWASP, XSS is in the top 3 web application vulnerabilities. Three types:

Protection: never insert user input into HTML without escaping. In PHP — htmlspecialchars() with ENT_QUOTES. In Laravel Blade templates — {{ $var }} is safe, {!! $var !!} is dangerous. In React — {variable} is safe, dangerouslySetInnerHTML is dangerous. For Rich Text — use htmlpurifier on PHP or DOMPurify in the browser.

CSRF: Protecting Forms and APIs

CSRF (Cross-Site Request Forgery) — an attacker forces the victim's browser to send a request on their behalf. Example: a user is logged into a bank, opens a malicious page, which makes fetch('https://bank.ru/transfer?to=evil&amount=50000') — if the bank is unprotected, money is transferred.

CSRF tokens — standard protection for forms: the server generates a random token, stores it in the session, and inserts it as a hidden field in the form. On POST request, the token is verified. The attacker does not know the token. Laravel does this automatically with @csrf.

SameSite cookies — modern protection: SameSite=Strict or SameSite=Lax prevents the browser from sending cookies in cross-site requests. Works in all modern browsers.

API without sessions (JWT, Bearer tokens) — CSRF is irrelevant if the token is not stored in a cookie (but in the Authorization header or localStorage). However, localStorage is vulnerable to XSS — so for sensitive data, HttpOnly cookies with SameSite are preferable.

WAF and DDoS Protection

WAF (Web Application Firewall) filters HTTP traffic for attacks: SQL injection, XSS, path traversal, known exploit patterns. Options:

• Cloudflare WAF — cloud-based, OWASP Top 10 rules out of the box, custom rules via expressions. Managed Rules automatically block new threats.
• ModSecurity (Nginx/Apache) — self-hosted, OWASP Core Rule Set (CRS). Flexible but requires tuning and monitoring of false positives.
• AWS WAF — for infrastructure on AWS, integrates with CloudFront and ALB.

DDoS protection. Cloudflare at L3/L4/L7 is the de facto standard for most sites. Automatic mitigation of volumetric attacks, Under Attack Mode during active attacks. For critical infrastructure — Cloudflare Magic Transit or specialized solutions (Qrator, StormWall for the Russian market).

Rate Limiting at the application level — an additional layer. Laravel ThrottleRequests middleware: 60 requests per minute per IP for general endpoints, 5 for /login and /password/reset. Redis as a counter store — mandatory for horizontally scalable systems (otherwise limits are not synchronized between servers).

Other Mandatory Measures

Security headers. Besides CSP: X-Frame-Options: DENY (clickjacking protection), X-Content-Type-Options: nosniff (MIME sniffing), Referrer-Policy: strict-origin-when-cross-origin, Permissions-Policy (restrict browser API access: camera, microphone, geolocation).

SQL injection. Prepared statements everywhere. No concatenation of user input into SQL strings. ORM (Eloquent, Doctrine) protects by default. $wpdb->prepare() in WordPress is mandatory.

Dependency updates. composer audit and npm audit in CI/CD pipeline. Dependabot or Renovate for automatic PRs with updates. Critical CVEs — patch within 24 hours.

Secrets and configuration. .env — never in Git. Secrets in production — via CI/CD environment variables (GitHub Secrets, GitLab CI Variables) or HashiCorp Vault. Leak detection: git-secrets, truffleHog in pre-commit hooks.

How We Work

1. Audit — code scanning, configuration review, dependency analysis, manual business logic verification.
2. Planning — vulnerability remediation plan, stack selection (CSP, WAF, rate limiting).
3. Implementation — TLS setup, CSP configuration, headers, Rate Limiting, WAF.
4. Testing — re-penetration test, load testing, false positive check.
5. Deployment and Monitoring — enable production CSP, set up alerts, train the team.

What's Included

• Report with found vulnerabilities and recommendations (PDF + code snippets)
• Ready TLS configuration (Nginx/Apache)
• CSP policy with Report-Only and production versions
• WAF and Rate Limiting setup
• Dependency update plan
• Access to monitoring tools (Sentry, Datadog)
• 30 days of post-audit support (consultations, fixes)

Timeline and Cost

The budget is calculated individually — contact us for a project evaluation.