1. How to Diagnose a Slow Site
When a site is slow, start by looking at these 3 metrics:
| Metric | What It Measures | Where the Problem Is |
|---|---|---|
| TTFB | Server response time | Hosting |
| Load Time | Total load time | Theme / Images / JS |
| CPU Usage | Server load | Hosting / Traffic |
| RAM Usage | Memory | Hosting |
| Request Count | Page weight | Software |
Diagnosing Problems by TTFB Value
| TTFB | Assessment |
|---|---|
| <150 ms | Excellent hosting |
| 150–300 ms | Good |
| 300–500 ms | Average |
| 500+ ms | Hosting is slow |
| 1000+ ms | Critical problem |
If TTFB is high, the problem is generally hosting.
2. The Most Common Hosting Error Codes
| Error | Meaning | Cause |
|---|---|---|
| 500 | Internal Server Error | PHP / RAM |
| 502 | Bad Gateway | Server overload |
| 503 | Service Unavailable | CPU limit |
| 504 | Gateway Timeout | Server not responding |
| 508 | Resource Limit | Hosting limit reached |
Identifying Problems by Error Code
| Error | Problem |
|---|---|
| 500 | PHP / software |
| 502 | Server under heavy load |
| 503 | CPU limit |
| 504 | Server slow |
| 508 | Insufficient resources |
3. Why Does a Site Go Down Intermittently?
The most common cause of this is exceeding the resource limit.
| Limit | Result |
|---|---|
| CPU limit | Site slows down |
| RAM limit | 500 error |
| Entry Process | 508 error |
| I/O limit | Site loads frozen |
4. How to Tell Whether It's Hosting or Software
The most important diagnostic table:
| Symptom | Problem |
|---|---|
| High TTFB | Hosting |
| Site slow in the evening | Traffic / CPU |
| Admin panel slow | RAM |
| Only homepage slow | Theme |
| Product pages slow | Database |
| Sometimes loads, sometimes doesn't | CPU limit |
| Constant 500 errors | RAM |
| 503 error | CPU |
| 508 error | Hosting plan |
5. Why Does a Site Crash When Traffic Spikes?
Cause: Concurrent user capacity.
| Concurrent Users | Required RAM |
|---|---|
| 5 | 512 MB |
| 10 | 1 GB |
| 20 | 2 GB |
| 50 | 4 GB |
| 100 | 8 GB |
If hosting capacity is insufficient for the concurrent user count, the site will crash.
6. Downtime Causes
| Cause | Description |
|---|---|
| Server maintenance | Planned downtime |
| Hardware failure | Disk / RAM |
| DDoS attack | Traffic |
| Software error | Update |
| DNS issue | Domain routing |
| Resource overflow | CPU/RAM |
7. Hosting Troubleshooting Checklist
When a problem occurs, check the following in order:
- [ ] What is the TTFB in ms?
- [ ] CPU usage %
- [ ] RAM usage %
- [ ] Disk I/O usage %
- [ ] Number of concurrent users
- [ ] What is the error code?
- [ ] Has a recent update been applied?
- [ ] Has traffic increased?
- [ ] Is DNS working?
- [ ] Is CDN working?
8. Quick Problem Identification Table
| Problem | Cause | Solution |
|---|---|---|
| Site very slow | CPU | VPS |
| Loads intermittently | CPU limit | Upgrade |
| 500 error | RAM | Increase RAM |
| 503 error | CPU | Increase CPU |
| 508 error | Limit | Upgrade hosting |
| High TTFB | Server | Switch hosting |
| Site fast at night | Traffic | Cache |
| Admin panel slow | RAM | Increase RAM |
Conclusion
80% of hosting problems stem from these 3 causes:
- Insufficient CPU
- Insufficient RAM
- Slow hosting infrastructure
That is why, when choosing hosting, the most important thing is:
Not disk space — it's CPU + RAM + Server quality