502 bad gateway とは (What is 502 Bad Gateway?)
The 502 Bad Gateway error is an HTTP status code (error 502) indicating that one server acting as a gateway or proxy received an invalid response from another “upstream” server. Think of it like a postal worker (gateway server) unable to deliver a package because the destination address (upstream server) provided incorrect or unreadable instructions. This error falls under server-side issues (500-level status codes), meaning users cannot fix it directly—resolution requires action from the website’s administrator or hosting provider.
Common messages Japanese users might see include:
- 502 Bad Gateway
- 502 Proxy Error
- HTTP 502
- サービスの一時的な過負荷 (Service Temporarily Overloaded).
502 bad gateway 意味 (Meaning of 502 Bad Gateway)
The core meaning of 502 Gateway lies in failed communication between servers. When you access a website, your request passes through multiple servers (e.g., proxy servers, load balancers, or CDNs). If any upstream server (e.g., an application or database server) responds with:
- Invalid data(e.g., corrupted, malformed, or empty responses),
- No response(due to crashes or timeouts),
the gateway server returns a 502 error instead of the expected webpage.
Unlike 504 Gateway Timeout (which signals a slow response), 502 explicitly means the response was unusable. For users, this translates to a broken browsing experience—often a blank screen or error page.
502 bad gateway 原因 (Causes of 502 Bad Gateway)
Server-Side Causes (～80% of cases):
- Server overload: Sudden traffic spikes (e.g., viral content or sales events) exhaust server resources (CPU, memory), causing crashes or incomplete responses.
- DNS misconfiguration: Incorrect IP mappings after domain/hosting changes prevent servers from connecting.
- Firewall/Security blocks: Overly aggressive security tools (e.g., Cloudflare, WordPress plugins) may mistake legitimate traffic for attacks and block upstream servers.
- Software issues: Bugs in PHP, outdated server software, or plugin conflicts (common in WordPress) disrupt server communication.
User-Side Causes (～20% of cases):
- Browser problems: Corrupted cache, outdated browsers, or conflicting extensions (e.g., ad blockers).
- Local network issues: Faulty routers or ISP glitches.
Table: Frequency of Common Causes
| Cause | Frequency | Examples |
| Server Overload | 40% | Traffic spikes, resource exhaustion |
| DNS/Firewall Issues | 30% | Misconfigured IPs, blocked requests |
| Software/Plugin Errors | 20% | PHP crashes, WordPress plugin conflicts |
| User-Side Issues | 10% | Browser cache, network problems |
502 bad gateway いつ治る (When Will 502 Bad Gateway Be Fixed?)
Recovery time depends entirely on the root cause:
- Minutes to hours:
- Temporary server overload (e.g., traffic surge ends).
- User-side fixes (e.g., clearing browser cache or restarting devices).
- Hours to days:
- DNS propagation delays (after server migrations).
- Hosting provider maintenance or server reboots.
- Days or longer:
- Complex server/software bugs (e.g., plugin conflicts requiring developer intervention).
- Infrastructure upgrades (e.g., scaling servers for sustained high traffic).
For users: Refresh the page after 5–10 minutes. If the error persists, check third-party tools like DownForEveryoneOrJustMe to confirm if the site is globally down.
Table: Recovery Time Estimates
| Cause | Typical Fix Time | Action Required |
| Temporary Server Overload | 5–30 minutes | Wait or refresh page |
| DNS Propagation | 1–48 hours | Wait for global DNS updates |
| Plugin/Software Fix | 2–24 hours | Developer troubleshooting |
| Server Upgrade | 1–7 days | Hosting provider intervention |
なにが502 bad gateway (What to Do About 502 Bad Gateway)
For Users:
- Refresh the page(Press F5 or Ctrl + R).
- Clear browser cacheor try incognito mode (bypasses corrupt cache/extensions).
- Switch browsers/devices(e.g., from Chrome to Edge).
- Restart your router(resolves local network glitches).
- Wait: If the issue is server-side, administrators likely already know.
For Website Administrators:
- Check server status: Look for overloads, crashes, or maintenance.
- Restart services: Reboot web servers (e.g., Nginx/Apache) or PHP engines.
- Review DNS/firewall settings: Ensure IP mappings and security rules are correct.
- Test plugins/themes: Deactivate WordPress plugins or switch themes to identify conflicts.
- Scale infrastructure: Use CDNs (e.g., Cloudflare) or load balancers to handle traffic surges.
Key Takeaways for Japanese Audiences
The 502 Bad Gateway error is a server communication failure, not a user-side problem. While frustrating, it’s often resolved quickly. Users should:
- Refresh or wait briefly.
- Rule out local issues (browser/router).
- Check outage-tracking sites.
Administrators should prioritize server health monitoring, traffic scaling, and DNS/firewall audits to minimize disruptions. For persistent issues, tools like server logs and uptime monitors (e.g., Semrush, Pingdom) are essential.
ℹ️ SEO Note: Frequent 502 errors can lower search rankings. Google may reduce crawl rates or drop pages from its index if downtime exceeds 6+ hours.