Introduction
HTTP status codes are like a short message from a web server, telling you how things went when it tried to handle your request. You‘re probably familiar with common ones like 404 Not Found or 500 Internal Server Error. But have you ever run into a 520 status code? It‘s a bit of a niche, Cloudflare-specific code that can be confusing if you don‘t know what it means or how to troubleshoot it.
Don‘t worry though, by the end of this article you‘ll be a 520 expert. We‘ll cover exactly what a 520 status code means, the most common causes for this error, and actionable steps you can take to fix and avoid 520s, whether you are a website owner or doing some web scraping. Let‘s dive in!
What is a 520 Status Code?
First off, it‘s important to note that a 520 is not an official HTTP status code you‘ll find in the specs. It‘s a proprietary status code created by Cloudflare, a popular CDN and security service that many websites use. So you‘ll only run into 520s on sites using Cloudflare.
In their docs, Cloudflare classifies a 520 status code as meaning "Unknown Error". Helpful, right? Basically it means that the origin web server behind Cloudflare responded with something unexpected or invalid.
You can think of Cloudflare as a middleman between visitors and the actual web server hosting a site. Normally Cloudflare takes a request, passes it to the origin server, gets the response, and passes that back to the visitor. But if the origin server‘s response is abnormal or missing required info, Cloudflare doesn‘t know what to do with it and throws a generic 520 status code.
Common Causes of 520 Errors
There are a number of reasons you might see a 520 error. Some common causes include:
1. Origin server is down – If the actual web server behind Cloudflare goes down, times out, or is unreachable, you‘ll likely get a 520.
2. Invalid HTTP response – Webservers need to return properly formatted HTTP responses, including status line, headers and body. If something is malformed or missing, it can trigger a 520.
3. Web application bugs – If the actual application code running on the origin server has bugs, exceptions or edge cases that return abnormal responses, those can come through to the user as 520s.
4. Missing required headers – Some sites require requests to include certain HTTP headers, like for authentication, rate limiting or security. Leaving those out can cause a 520.
5. Automated requests blocked – If a site detects unusual automated request patterns, its security system might block those requests, often resulting in a generic 520 to hide the real cause.
So in summary, 520s usually mean the problem is with the origin web server itself, or that your request was missing some required components. It‘s a vague error that can take some digging to pinpoint the true source of.
How to Fix and Avoid 520 Errors
Now that you understand what a 520 error means and some common causes, what can you actually do about it? The answer depends on whether you are the owner of the website throwing a 520, or you‘re trying to scrape a site and avoid 520 blocks. Let‘s look at some tips for each case.
For Website Owners
If you are seeing 520 errors for your Cloudflare-backed website, here are some steps you can take to debug and fix the issue:
Check server health – First, make sure your origin server is actually up and reachable. Use monitoring tools to verify the server stays responsive and isn‘t overloaded.
Review error logs – Check your server‘s error logs for any exceptions or abnormal requests that may be causing malformed responses. Fix any underlying bugs.
Validate response format – Verify that your application code is always returning properly formatted HTTP responses, with status, headers, and body. Make sure edge cases are accounted for.
Configure request timeouts – If some requests are taking too long and timing out, causing 520s, consider increasing timeout settings or optimizing slow code.
Test different URL paths – See if the 520 only happens on specific pages or URL patterns. That can help isolate code that needs fixing.
Check for missing headers – If your code expects certain headers like for CORS or authentication, make sure those requirements are documented and handled properly.
Fixing 520s from the server side is often a process of elimination, checking for common issues and zeroing in on the scope and cause. Cloudflare‘s generic 520 error doesn‘t give many clues itself.
For Web Scrapers
If you are trying to scrape a website but getting blocked by 520 status codes, here are some tips to get around them:
Check for missing headers – Inspect the site‘s normal request patterns and make sure you are including all expected headers, like User-Agent, Referer, Accept-Language, etc.
Avoid abnormal request patterns – Space out requests and don‘t hit a site too rapidly. Avoid repeated retries for failures. Randomize access patterns.
Use undetectable automation tools – Headless browsers like puppeteer are easily detectable. Switch to an undetectable tool like undetected-chromedriver.
Implement proxy rotation – Rotate request IP addresses using a proxy service to avoid rate limits and blocks. Rotating data center IPs or residential IPs through a provider like ScrapingBee can help avoid IP bans.
Verify request URLs – Make sure the URLs you are requesting are valid and haven‘t changed. A single typo can cause 520 errors.
Respect robots.txt – While not always required, respecting a site‘s robots.txt rules can often help avoid heavy-handed blocking that results in 520s.
The key to avoiding 520 blocks while scraping is to minimize things that make your request patterns look different from normal users. Careful rate limiting, realistic headers and undetectable tools are the way to go.
Conclusion
While a 520 status code can seem like a vague and mysterious error at first, with the knowledge from this article you should now have a solid understand of what it means and how to go about fixing it.
Remember, 520 means the origin server gave an unexpected response, maybe because of an outage, invalid HTTP formatting, missing security headers, or automated request blocking. As a website owner, focus on server health, proper response handling and clear header requirements to resolve 520s. And as a web scraper, dial in your request patterns, use undetectable tools and proxies, and respect the site‘s rules. With some analysis and iteration, those pesky 520 errors will be a thing of the past.
