502 Bad Gateway
Example HTTP Response
HTTP/1.1 502 Bad Gateway
Content-Type: text/html
<h1>Bad Gateway</h1>- Upstream server is down
- Proxy received invalid response
- Backend server crashed
What does this mean?
Lost in translation! The middleman server got gibberish from the backend. Like a game of telephone gone wrong.
Technical Definition
The server was acting as a gateway and received an invalid response from the upstream server.
RFC Says
"The 502 (Bad Gateway) status code indicates that the server, while acting as a gateway or proxy, received an invalid response from an inbound server it accessed while attempting to fulfill the request."
Plain English:
502 means 'I'm a proxy/gateway, and the server behind me sent back a response I couldn't understand or process.' This is common when a reverse proxy (like nginx or a load balancer) can't communicate properly with your application server - maybe your app crashed, returned invalid HTTP, or the connection broke.
Common Misinterpretation
Don't return 502 from your application code for downstream API failures - use 500 or 503 instead. 502 should come from infrastructure layer (reverse proxies, load balancers, API gateways) when they can't get a valid response from your app.
Ready-to-use code for returning this HTTP status in your application:
// Express.js
app.get('/example', (req, res) => {
res.status(502).json({
error: 'Bad Gateway',
message: 'Your error message here'
});
});
// Native HTTP
const http = require('http');
http.createServer((req, res) => {
res.writeHead(502, { 'Content-Type': 'application/json' });
res.end(JSON.stringify({
error: 'Bad Gateway',
message: 'Your error message here'
}));
}).listen(3000);- Proxy/gateway received invalid response from upstream server
- Backend server returned malformed data or crashed mid-response
- Use when your server is a proxy and upstream failed
- Use 504 if the issue is timeout rather than bad response
Indexing
Like 500, temporary 502 errors don't immediately affect indexing. Google retries before making indexing decisions.
Crawler Behavior
Crawlers interpret 502 as temporary infrastructure issues and will retry. Persistent 502s hurt crawl efficiency.
Google Notes
502 errors often indicate deployment or infrastructure problems. Google is forgiving of brief outages but persistent issues affect rankings.
502 Bad Gateway FAQ
What causes a 502 Bad Gateway error?
Upstream server is down. Proxy received invalid response. Backend server crashed.
When should I use 502 Bad Gateway?
Proxy/gateway received invalid response from upstream server. Backend server returned malformed data or crashed mid-response. Use when your server is a proxy and upstream failed. Use 504 if the issue is timeout rather than bad response.