乐闻世界logo
搜索文章和话题

What is the CDN troubleshooting process? What are the common tools?

2月21日 16:59

Importance of CDN Troubleshooting

As the traffic entry point for websites and applications, CDN failures directly affect user experience and business availability. Mastering CDN troubleshooting methods and techniques enables quick identification and resolution of issues, minimizing failure impact.

Common CDN Failure Types

1. Access Failures

Symptoms:

  • Users cannot access website
  • Returns 5xx errors
  • Connection timeout

Possible causes:

  • CDN node failure
  • DNS resolution issues
  • Origin server failure
  • Network connection issues

2. Performance Degradation

Symptoms:

  • Slow response time
  • Frequent buffering (video)
  • Extended loading time

Possible causes:

  • Low cache hit rate
  • Network congestion
  • High origin server load
  • CDN node overload

3. Content Inconsistency

Symptoms:

  • Users see old content
  • Different regions see different content
  • Updates not taking effect

Possible causes:

  • Cache not refreshed
  • TTL set too long
  • Incorrect cache key configuration
  • Inconsistent multi-CDN configuration

4. Security Issues

Symptoms:

  • DDoS attacks
  • Malicious crawler access
  • Data leakage

Possible causes:

  • Improper security configuration
  • Insufficient protection strategies
  • Unpatched vulnerabilities

Troubleshooting Process

1. Confirm Failure Scope

Check steps:

1. Confirm user scope

bash
# Check if many users are reporting
# View monitoring data
# Analyze error logs

2. Confirm geographic scope

bash
# Check if specific regions are affected
# Use geographic location tools
# Analyze access logs

3. Confirm time scope

bash
# Check when failure started
# View time series data
# Compare with historical data

2. Check CDN Status

Check items:

1. CDN node status

bash
# Check node health status
curl -I https://cdn.example.com/health

# Check multiple nodes
for node in node1 node2 node3; do
  curl -I https://$node.example.com/health
done

2. CDN console

  • View node status
  • Check alert information
  • Analyze traffic charts

3. CDN API

javascript
// Use CDN API to check status
const response = await fetch('https://api.cdn.com/status', {
  headers: {
    'Authorization': 'Bearer {api_token}'
  }
})
const status = await response.json()
console.log(status)

3. Check DNS Resolution

Check steps:

1. Check DNS resolution

bash
# Check domain resolution
dig example.com

# Check specific DNS server
dig @8.8.8.8 example.com

# Check CNAME record
dig CNAME cdn.example.com

2. Check DNS propagation

bash
# Check multiple DNS servers
for dns in 8.8.8.8 1.1.1.1 114.114.114.114; do
  echo "DNS: $dns"
  dig @$dns example.com
done

3. Check DNS cache

bash
# Clear local DNS cache
# macOS
sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder

# Linux
sudo systemctl restart nscd

4. Check Network Connection

Check steps:

1. Check network latency

bash
# Ping test
ping cdn.example.com

# Traceroute test
traceroute cdn.example.com

# MTR test (combines ping and traceroute)
mtr cdn.example.com

2. Check port connection

bash
# Check HTTP port
telnet cdn.example.com 80

# Check HTTPS port
telnet cdn.example.com 443

# Use nc to test
nc -zv cdn.example.com 443

3. Check SSL/TLS

bash
# Check SSL certificate
openssl s_client -connect cdn.example.com:443 -servername cdn.example.com

# Check SSL certificate validity
echo | openssl s_client -connect cdn.example.com:443 2>/dev/null | openssl x509 -noout -dates

5. Check Cache Status

Check steps:

1. Check cache hit rate

bash
# Analyze access logs
grep "HIT" access.log | wc -l
grep "MISS" access.log | wc -l

# Calculate cache hit rate
hit_count=$(grep "HIT" access.log | wc -l)
total_count=$(wc -l < access.log)
hit_rate=$((hit_count * 100 / total_count))
echo "Cache hit rate: $hit_rate%"

2. Check cache keys

bash
# Check cache key configuration
nginx -T | grep proxy_cache_key

# Analyze cache key differences
grep "cache_key" access.log | sort | uniq -c

3. Check cache expiration

bash
# Check cache TTL
curl -I https://cdn.example.com/file.jpg | grep -i cache-control

# Check cache expiration time
curl -I https://cdn.example.com/file.jpg | grep -i expires

6. Check Origin Server Status

Check steps:

1. Direct access to origin

bash
# Direct access to origin for testing
curl -I https://origin.example.com/file.jpg

# Check origin response time
time curl https://origin.example.com/file.jpg

2. Check origin load

bash
# Check CPU usage
top

# Check memory usage
free -h

# Check disk usage
df -h

# Check network connections
netstat -an | grep ESTABLISHED | wc -l

3. Check origin logs

bash
# Check error logs
tail -f /var/log/nginx/error.log

# Check access logs
tail -f /var/log/nginx/access.log

# Check slow queries
tail -f /var/log/mysql/slow.log

Common Troubleshooting Tools

1. Network Diagnostic Tools

Ping

bash
# Basic usage
ping cdn.example.com

# Specify count
ping -c 10 cdn.example.com

# Specify packet size
ping -s 1024 cdn.example.com

Traceroute

bash
# Basic usage
traceroute cdn.example.com

# Use ICMP
traceroute -I cdn.example.com

# Specify port
traceroute -p 443 cdn.example.com

MTR

bash
# Basic usage
mtr cdn.example.com

# Specify report mode
mtr -r -c 10 cdn.example.com

# Save to file
mtr -r -c 10 cdn.example.com > mtr_report.txt

2. HTTP Debugging Tools

Curl

bash
# Basic request
curl https://cdn.example.com/file.jpg

# View response headers
curl -I https://cdn.example.com/file.jpg

# View detailed information
curl -v https://cdn.example.com/file.jpg

# View request and response headers
curl -i https://cdn.example.com/file.jpg

# Specify request headers
curl -H "User-Agent: Mozilla/5.0" https://cdn.example.com/file.jpg

# View response time
curl -w "@curl-format.txt" -o /dev/null -s https://cdn.example.com/file.jpg

curl-format.txt:

shell
     time_namelookup:  %{time_namelookup}\n
        time_connect:  %{time_connect}\n
     time_appconnect:  %{time_appconnect}\n
    time_pretransfer:  %{time_pretransfer}\n
       time_redirect:  %{time_redirect}\n
  time_starttransfer:  %{time_starttransfer}\n
                     ----------\n
          time_total:  %{time_total}\n

Wget

bash
# Basic download
wget https://cdn.example.com/file.jpg

# View detailed information
wget -d https://cdn.example.com/file.jpg

# Save response headers
wget -S https://cdn.example.com/file.jpg

# Specify timeout
wget -T 10 https://cdn.example.com/file.jpg

3. Browser Developer Tools

Network Panel

View request details:

  • Request URL
  • Request method
  • Request headers
  • Response headers
  • Response time
  • Status code

View waterfall chart:

  • Request timeline
  • Wait time
  • Download time
  • Total time

Console Panel

View error messages:

  • JavaScript errors
  • Network errors
  • Resource loading errors

4. Log Analysis Tools

ELK Stack

Elasticsearch query:

json
// Query specific errors
{
  "query": {
    "match": {
      "status": 502
    }
  }
}

// Query specific time range
{
  "query": {
    "range": {
      "@timestamp": {
        "gte": "2026-02-19T00:00:00",
        "lte": "2026-02-19T23:59:59"
      }
    }
  }
}

Kibana visualization:

  • Request volume trend chart
  • Error rate distribution chart
  • Response time distribution chart

AWStats

Analyze access logs:

bash
# Generate report
awstats.pl -config=cdn -update

# View report
awstats.pl -config=cdn -output

Troubleshooting Cases

Case 1: Slow Website Access

Problem description: Users report slow website loading

Troubleshooting steps:

1. Check CDN nodes

bash
# Ping test
ping cdn.example.com

# Check response time
curl -w "@curl-format.txt" -o /dev/null -s https://cdn.example.com/

2. Check cache hit rate

bash
# Analyze access logs
grep "MISS" access.log | wc -l

3. Check origin

bash
# Direct access to origin
curl -w "@curl-format.txt" -o /dev/null -s https://origin.example.com/

4. Solutions:

  • Improve cache hit rate
  • Optimize origin performance
  • Add CDN nodes

Case 2: Content Update Not Taking Effect

Problem description: After updating content, users still see old content

Troubleshooting steps:

1. Check cache TTL

bash
# Check cache control headers
curl -I https://cdn.example.com/file.jpg | grep -i cache-control

2. Check cache keys

bash
# Check cache key configuration
nginx -T | grep proxy_cache_key

3. Check cache status

bash
# Check if cache is hit
curl -I https://cdn.example.com/file.jpg | grep -i x-cache

4. Solutions:

  • Refresh CDN cache
  • Use versioning
  • Adjust TTL settings

Case 3: HTTPS Certificate Error

Problem description: Browser shows certificate error

Troubleshooting steps:

1. Check SSL certificate

bash
# Check certificate information
openssl s_client -connect cdn.example.com:443 -servername cdn.example.com

# Check certificate validity
echo | openssl s_client -connect cdn.example.com:443 2>/dev/null | openssl x509 -noout -dates

2. Check certificate chain

bash
# Check certificate chain integrity
openssl s_client -connect cdn.example.com:443 -showcerts

3. Solutions:

  • Update SSL certificate
  • Configure complete certificate chain
  • Check certificate configuration

Failure Prevention Measures

1. Monitoring and Alerting

Key metrics:

  • Node availability
  • Response time
  • Error rate
  • Cache hit rate

Alert configuration:

yaml
# Prometheus alert rules
groups:
  - name: cdn_alerts
    rules:
      - alert: HighErrorRate
        expr: cdn_errors_total / cdn_requests_total * 100 > 1
        for: 5m
        labels:
          severity: critical
        annotations:
          summary: "High error rate detected"

2. Health Checks

Regular checks:

bash
# Health check script
#!/bin/bash
while true; do
  status=$(curl -s -o /dev/null -w "%{http_code}" https://cdn.example.com/health)
  if [ $status -ne 200 ]; then
    echo "Health check failed: $status"
    # Send alert
  fi
  sleep 60
done

3. Backup and Disaster Recovery

Backup strategy:

  • Regularly backup configurations
  • Backup SSL certificates
  • Backup DNS records

Disaster recovery plan:

  • Multi-CDN strategy
  • Origin redundancy
  • Automatic failover

Interview Points

When answering this question, emphasize:

  1. Mastery of systematic troubleshooting process
  2. Proficiency in using various troubleshooting tools
  3. Practical troubleshooting experience
  4. Ability to quickly identify and resolve issues
  5. Awareness of failure prevention and disaster recovery
标签：CDN
热门标签
更多
Git(114)C语言(23)C++(15)React(34)前端(148)Cypress(27)JavaScript(56)Linux(20)Rust(10)Docker(65)Mongoose(18)TypeScript(27)MySQL(8)Vue(13)Tailwind CSS(29)CSS(19)ElasticSearch(24)网络(12)TypeORM(31)