The Service Unavailable 503-error is an HTTP status code that means a web server is temporarily incompetent to handle a request. The 503 error is different from a 500 Internal Server Error. internal server error 500 means something is wrong on the website's server but the server can't be able to tell what the exact problem in it.
While an error 503 happens when the server is overflow with requests or is having maintenance performed on it. Most of the time, it occurs because the server is much busy or because there's maintenance being performed on it.
Here are the slightly different names for this error in which you might see the "service unavailable" error such as:
HTTP Server Error 503 can appear in any browser in any operating system, including Windows 10 to Windows XP, macOS, Linux, etc. Your smartphone or other nontraditional computers also show 503 error. If these devices have internet access, then you could see a 503 in other situations.
The 503 error displays inside the browser window, just like web pages do.
The 503 error is a server-side error, that means the problem is usually with the website's server.
Nonetheless, here are few quick things you can try against the HTTP 503 error to appear on the server side
Restart/Reboot your server:
Sometimes, there will be crowd in the server chain that hosts your website. Here one of the most effective and simplest solution is that to open up server and restart the web server hosting the application. If your website is hosted over the multiple servers, make sure that are all servers are rebooted in the proper manner so the system is come back online as normal. A 503 error code could be a result of a blockage somewhere in the server chain that hosts your application, however a simple reboot could refresh everything and get you back up and running.
Check to see if your web server’s is going through maintenance:
Most of the web servers are shut down when they're going through maintenance. If you have the access of your server’s administrator settings, check the configuration options to see when automatic maintenance sessions are scheduled. If you have the complete control over server’s maintenance, so you can disable these automatic updates in the configuration options.
Improper Firewall Configuration:
A firewall is a primary security device that acts as a gatekeeper and monitors network traffic, deciding which traffic is safe and which could be hostile or distributed denial-of-service (DDoS) attacks. In most cases, all potentially harmful traffic is stopped.
Sometimes, a defective firewall configuration will cause your firewall to consider requests from a content delivery network(CDN) as an attack on your server and refuse them, resulting in a service unavailable Error show. Check your firewall configuration to find and fix the issue.
However, automatic firewall services sometimes can perform false positives, mistaking perfectly safe and valid content from CDNs or elsewhere as harmful, thereby shutting off that flow of content in an instant, that can lead to a service unavailable 503 Error.
Sift through your server-side logs:
Server side logs are of two types applications logs and server logs. Application logs recount the website’s whole history, allowed you see the web pages requested by visitors and the servers it connected to.
Server logs render your information about the hardware running on your server, divulge details about its health and status. You can sift through both types of server-side logs to expose an alarming information about your server or website.
Check for Unexpected Maintenance:
you may be not knowing, but your server or application may be go down for maintenance automatically. Many latest content management systems like WordPress will automatically download and install updates to their base software without any collaboration on your behalf. The web server could be furnishing 503 Service Unavailable Errors during this period, especially if your application is appointed on a slower server or a shared host. If you have the administration settings access, disabling configuration options for automatic maintenance scheduling. But don't forget to upgrade on newer versions fairly regularly, because they have included critical security fixes.
Server Connectivity Issues:
It's possible that a HTTP 503 error indicates that a server somewhere in the chain is down or unreachable for any reason. Most latest applications don't appointed on a single server, but it may be spread over multiple systems, or rely on many third-party services to function. If anyone server is down for maintenance or otherwise inaccessible from these server’s chain, this could result in an http 503 error.
Check the Logs:
almost every web application or web site will keep some form of server-side logs. Application logs are the history of the application what they did, such as which pages were requested, which servers it connected to, which database results it provides, and so on.
Server logs are related to the actual hardware that is running the application, and it will often provide details about the status and health of all connected services, or even just the server itself.
Comb through your website’s code to find bugs:
Sometimes the 503 service unavailable appear due to the mistake in the website's code. It is possible your web server may not be able to correctly answer requests from a content delivery network. So you can Comb through your code to find bugs. it may be that a problem in some custom code within your application is causing the issue. For debugging of error make a copy of the entire application to a local development machine and perform a step by step debugging process, which will allow you to redevelop the new scenario in which the error 503 occurred and view the application code now this time something goes wrong.
Error from client side:
The HTTP 503 error is a server-side error, but It is possible that your computer is having some kind of problem that's causing the service unavailable 503 but it's not commonly.
Whatever, there are a few things you can try on your end.
Refresh the page:
Sometimes 503 error is very temporarily. So before you go to the deep on the error, you must reload the webpage by pressing F5 or Ctrl+R or retry the URL from the address bar by clicking the reload/refresh button. This simple step may be resolved your issue.
Restart Your Devices:
It is possible, this is may be some temporary issue with your computer and networking equipment like Wifi, router, modem, etc have some temporary issues. Simply you restart your computer and networking devices.
If the rebooting of your computer and other networking devices don't resolve the error 503 it's means, there may be a fault with the DNS configuration of the computer or the router.
In the case of a problem with a selected DNS server, it may be fixed by choosing another DNS server to use.