What Does “502 Bad Gateway” Mean, Actually?

Key Points:

• “502 Bad Gateway” informs you that while the machine was attempting to act as a proxy or gateway, it received an invalid response from the server.
• The HyperText Transfer Protocol is an application layer protocol for the Internet protocol suite model for use in distributed, collaborative, hypermedia information systems.
• When too many people are trying to access data from the same server, the server can become overwhelmed with the number of requests it’s receiving and start producing invalid responses.

“502 Bad Gateway” is a type of error message that users may get when using the internet. It’s a HyperText Transfer Protocol error message that indicates an issue with communication between your device and the server where the information you’re trying to access is stored.

In full, it suggests that while the machine was attempting to act as a proxy or gateway, it received an invalid response from the server.

There are many possible reasons for a 502 Bad Gateway error code. However, the most common is server overload. When the server is overloaded with requests for information, it can have difficulties sending out information packets at the right intervals. When these packets come into the proxy or gateway device at the wrong intervals or with incorrect information, it triggers a 502 Bad Gateway error.

What is “502 Bad Gateway”?: Exact Definition

“502 Bad Gateway” is an error code for the HyperText Transfer Protocol that indicates that the gateway device received an invalid response from the server it was trying to connect with.

How Does “502 Bad Gateway” Work?

Understanding how the 502 Bad Gateway error works relies on your knowledge of the HyperText Transfer Protocol. Succinctly, the HyperText Transfer Protocol is an application layer protocol for the Internet protocol suite model for use in distributed, collaborative, hypermedia information systems. But what do all those fancy tech words mean?

“Application layer” refers to layers of abstraction. In computing, it’s common to hide the inner workings of a system behind applications that include things like graphical user interfaces to improve usability. After all, not everyone can read and write programming languages, and even those who can program typically can’t read and write every individual language.

By putting an application layer on top of your code, you mask the backend code behind an application that the layperson can use.

The “Internet protocol suite” or Transmission Control Protocol/Internet Protocol (TCP/IP) is a set of systems and rules used in data transmission via the internet. These systems and regulations determine how each process must be run and provide a standardized method of data transmission that anyone can implement.

HyperText Transmission Protocol, or HTTP, is the foundation-level protocol for internet transmission. Thus, it’s used by every company that interacts with the internet. HTTP is used for transferring data between servers and displaying HyperText Markup Language (HTML) information in a graphical interface that laypeople can use.

HTTP implementations use ports or dedicated endpoints that direct the flow of information. Typically, port 80 will be used for unencrypted data transfer, while port 443 will be used for encrypted data transfer. Data will be transferred through the ports between the server that the data is hosted on and the device requesting the data.

HTTP works on a system of request-response messages. Essentially, your computer will request data from the server, and it’s up to the server to send back the correct data. For instance, if you load a simple webpage like Wikipedia, you have to load all of the assets associated with the page, such as the Wikipedia logo.

When your computer goes to load a Wikipedia page, it sends a request to the server saying, “send me the information stored on XYZ page,” and the server responds with the data. If the server doesn’t react with the information, you’ll get a 502 Bad Gateway error.

How Do I Fix a “502 Bad Gateway” Error?

“502 Bad Gateway” errors can typically be fixed by simply reloading the page. Though, if you’re here, we suspect you’ve already tried that. The most common issue that causes servers to return “502 Bad Gateways” is server overload.

Servers are generally designed to handle transferring large volumes of data, but even the most robust servers have limits. When too many people are trying to access data from the same server, the server can become overwhelmed with the number of requests it’s receiving and start producing invalid responses. When this occurs, users will begin to see “502 Bad Gateway” errors when loading pages and information from the server.

Fixing a “502 Bad Gateway” as a User

Fixing a “502 Bad Gateway” as a user differs from fixing it as a system administrator. Thus, we’ve separated this section into a section for user fixes and admin fixes.

Step 1: Reload the Page

Most “502 Bad Gateway” errors can be fixed by reloading the page once or twice. When you reload the page, you send a new request for information to the server. If the server was a bit overloaded when you sent your first request, the traffic might have calmed down a little by the time you sent a second request, allowing you to access the data.

Step 2: Look for Connectivity Issues

This one is a bit harder since it can be challenging to ascertain whether a connectivity issue is on your or the server’s side. The easiest way to tell if it’s you or them is to use a server uptime detector like DownDetector to see if other people are also having server issues.

Sites like DownDetector don’t just tell you if the server is down according to the requests sent by the site. They typically also track reports of difficulties from users as well. If you see that many other users have recently had issues connecting with the site in question, you’ll want to try again later.

Connectivity issues can also be on the part of your internet service provider (ISP). So, be sure to check to see if your area is currently experiencing an outage or service disruption that might be causing you to have trouble connecting to web servers.

Fixing a “502 Bad Gateway” as a System Administrator

Fixing a lousy gateway as a system administrator is significantly more in-depth than fixing it as a user. Users don’t have much agency over the server status or information, but system administrators do. Thus, system administrators will need to work harder to diagnose the problem with their website to ensure that the website’s uptime isn’t too negatively impacted.

Step 1: Look for Connectivity Issues

The first thing system admins will want to look at regarding “502 Bad Gateway” errors is their server’s connectivity. Ensuring that your server is functioning as intended is the first step to diagnosing problems with your website.

Typically, websites are hosted on a third-party server, and these servers decide to do their maintenance independently from the users. In this sense, system admins are both users and administrators. They’re users of a third-party server that they use to host the website for which they are the administrator.

Check to see if your website’s server is currently down for maintenance. If so, you’ll have to wait for maintenance to complete to see if your website comes back up. Often, server maintenance is the cause of an errant “Bad Gateway” error.

Step 2: Check for DNS Changes

When you host a website, it’s hosted using a Domain Name Service, or DNS. This unique identifier is an IP address that stores all the information for your website and identifies it among other websites. It’s a string of data comprehensible to computers, servers, and other devices.

The Domain Name is the alphanumeric address for your website. For instance, the domain name for Google is “google.com.” It differs from the URL as the Domain Name refers to the space on the internet where the data is located, while the URL points to specific data. Cloudflare gives the example of “cloudflare.com” being their domain name while “/learning/” would be the URL, giving you a full address of “cloudflare.com/learning/” to reach their learning page.

Changes to the DNS can take several hours to reflect on the website, which can cause the site to go down while these changes are processed. Any change to your DNS or DNS registration information could cause your website to go down. However, you should still update your DNS information whenever necessary, even if it causes the website to go down for a few hours.

Step 3: Check Site Logs

Site logs are the best place to look for issues if you understand how to read them. Understanding your site’s logs is an excellent move that every system admin should make, especially as their site grows.

Server logs can show you tons of information you’ll need to effectively run and manage your site, such as individual server requests and even revealing hacks, distributed denial-of-service (DDOS), and breach information. So, it’s an excellent place to start looking for the source of your “502 Bad Gateway” errors.

Step 4: Check Your Firewall

Firewalls exist all over the internet; they’re not limited to personal computer use. Your server will have a pre-installed firewall to protect it from viruses, hackers, and DDOS attacks. This firewall will act as a guardian between your site’s data and those who would do it harm.

However, firewalls aren’t foolproof. It’s possible for a firewall to fail by triggering a false positive, just like it’s possible to fail and trigger a false negative. When your firewall is too overzealous with blocking connections, it can start to trigger “502 Bad Gateway” errors when people visit your website.

Step 5: Check Code for Bugs and Discrepancies

This step is crucial for users of platforms like WordPress and Squarespace, which rely on graphic editors for web pages. HTML editors that use a graphical user interface often create accidental discrepancies in the HTML that can only be fixed on the HTML side (or by scrapping your project and starting over again.)

While it’s not excessively common, these bugs and discrepancies in the code of your website can and will cause severe errors, including “502 Bad Gateways.” So, if your logs, firewall, DNS, and connectivity are all OK, this is an excellent spot to look for issues that might be causing your website to not appear at the designated URL.

Step 6: Contact Your Hosting Service

The last step should be contacting your hosting service to see if they have insight into why your website isn’t loading correctly. Sometimes errors and server issues fly under the radar with larger hosting companies and giving them a call can be the kick in the butt they need to get to fixing these issues.

If there is an issue with your broader server performance on the host’s side, you’re likely not the only website affected. So, don’t feel bad about contacting them if your website has been down for an extended period.

How Do You Create a “502 Bad Gateway” Error?

Overloading a server is the easiest way to trigger a “502 Bad Gateway” error. This can typically be done by sending hundreds of requests for information to the server in a short period.

However, do not attempt to intentionally create a 502 Bad Gateway on someone else’s website. This is called a distributed denial-of-service or DDOS attack, and it is illegal in the United States of America. People found to be engaging in DDOS attacks may face a prison sentence or fine if caught.

What are the Applications of “502 Bad Gateway” Errors?

“502 Bad Gateway” errors are designed to convey server information to admins. That is their purpose and sole application (unless you count DDOS attacks).

Final Thoughts

“502 Bad Gateway” errors can be frustrating. Luckily fixing them is much easier than triggering them. Contact customer service for your website’s hosting if you’re struggling with a “Bad Gateway” error and can’t diagnose the problem. They’ll be able to guide you through the problem and help you fix it.

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