503 Error - What is it, what causes it & How to fix it
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Seeing a 503 error code when trying to load your website can be very stressful and confusing, not to mention that it drives your visitors away. That is why understanding what a 503 Service Unavailable error means, its causes, and how to fix it is key to maintaining an active, welcoming website.
HTTP Status codes from the 5xx branch denote server-side errors. Such errors are:
- 500 (Internal Server Error)
- 502 (Bad Gateway)
- and (504 Gateway Timeout Error).
In this article, we’ll help you understand what is the 503 Service Unavailable error, common solutions, and the main causes for it. So keep reading!
Unlike other errors like 404 Not Found, which indicate a client-side issue, a 503 error is a server-side problem. Thus, it requires intervention from the website administrator or hosting provider. Understanding this distinction is crucial for effectively troubleshooting and resolving the issue.
How to identify the HTTP Error 503?
Understand the wording of the error message
The 503 error message can vary depending on the server and configuration but usually includes phrases like “Service Unavailable” or “HTTP Error 503.”
Generally, the error message may look something like this:
Or it can be shown as a custom error page, like the following error representation:
That is why understanding the specific wording can provide clues about the underlying issue. For example, some messages might indicate that the server is undergoing maintenance, while others might suggest that the server is overloaded.
Check your server/application logs
Error logs are a helpful asset when troubleshooting an issue with your site. These entries provide context and give a direction to your investigation. There are two main types of logs you should focus on and here we’ll review them in more detail, so keep reading.
Server logs
Checking server logs can provide detailed information about what might be causing the 503 error. These logs can offer insights into server resource usage, failed processes, or other anomalies. In general, you can review your server logs from your web hosting control panel.
SiteGround clients can examine server logs via Site Tools > Statistics > Access Logs, as in the image below:
For more options on accessing your SiteGround server logs, refer to our article – How to Find the Raw Access Logs for my website?
In the logs, look for error messages or warnings that occurred around the time the error was reported.
WordPress Logs
The debug log can also be a valuable resource for identifying issues if you’re running a WordPress site. In web applications like WordPress, a 503 error can be related to plugins, themes, or other components – so look for similar entries.
Keep in mind the error log is not active by default in WordPress, and you must enable it manually. For more detailed steps on enabling error logging in WordPress, read our article on “How to Find and Access WordPress Error Logs.”
Inspecting the debug log in WordPress can help you narrow down the exact cause of the 503 error.
Troubleshooting tools to use
Besides combing through logs, checking your resource usage when you’ve encountered a 503 error is helpful. High CPU, memory, disk I/O, and bandwidth usage can all indicate server strain. Often, that is due to inefficient code, resource-intensive plugins, high traffic, or DDoS attacks.
Therefore, you should check your server’s behavior in your hosting account or if there is a notification of ongoing server maintenance.
SiteGround clients can check resource usage from their Client Area > Services > Hosting > Manage > Statistics. Examining these metrics in your SiteGround Client Area can reveal patterns that lead to server overload.
Now that you’ve identified the possible source of the error, you can begin solving the problem.
How to fix the 503 Service Unavailable error?
After pinpointing the possible reason for the 503 Service Unavailable error, roll up your sleeves and start testing solutions.
Here, we’ll guide you through the most common solutions, so read on.
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Refresh the page
Sometimes, the 503 error is only temporary. And in such cases, a simple page refresh can help you bypass the HTTP 503 error. This is especially true if the server is momentarily overloaded.
You can refresh the page using the Reload this page button in the browser as in the screenshot below or Ctrl + R / Cmd + R (Windows/MacOS, respectively).
If it was a temporary problem, refreshing the page may be the solution. However, if the same issue persists after reloading the page, you must investigate further.
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Check the status of your server
Next, you should examine your web hosting account to check your server status. Your host should notify you in case of planned server maintenance or a global server issue. That is standard practice, as servers may respond with all sorts of errors (like the HTTP response 503) during maintenance.
If the server is experiencing a high load due to a DDOS attack, there should also be a notification or a support ticket. In such cases, you’ll be advised to turn on your CDN’s DDoS protection. That will restrict overall access to your site until the attack is mitigated.
The state of your server would also include any global issues that may be affecting your web server’s performance or state.
In case, none of that applies to the status of your server, proceed with the next solution.
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Examine Firewall settings
Firewalls are an indispensable part of web security. However, faulty firewall configurations can also disrupt access to your site with a 503 Service Unavailable.
Such blocks may occur if your firewall settings are overly strict or if your request hits a server firewall security rule. Sometimes, there may be false positives, and they may block legitimate requests.
So, if you are using a security plugin to protect your site, you may need to review and verify your settings. Make sure your IP address is added to your site’s whitelist. Depending on the type of IP address your ISP has assigned to you – dynamic or static IP – you may need to whitelist an entire IP range (IPv4 or IPv6).
If you do not find any issues with your website firewall configuration, your IP or request may be blocked on a server level. Thus, you will need to contact your hosting support team so they can review the firewall settings or unblock your IP address, if necessary.
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Optimize Your Website
Optimizing your WordPress website is crucial for resolving a 503 error because it helps reduce server load and improves overall performance. When your site runs efficiently, it’s less likely to become overwhelmed during traffic spikes, which can trigger a 503 error.
Here is what you can do to optimize your WordPress site and improve its performance to reduce server load.
SuperCacher
SiteGround customers can easily take advantage of SuperCacher, a 3-layered caching service. You can find and manage it in your Site Tools > Speed > Caching. Each layer optimizes a particular website aspect, as follows.
- NginX Direct Delivery. This feature speeds up static content delivery, like images and CSS files.
- Dynamic Caching caches dynamic content to reduce server load and improve load times.
- Memcached is object caching that stores frequently accessed data in memory to speed up database queries and reduce load.
SiteGround Speed Optimizer
The SiteGround Speed Optimizer is an efficient way to improve your WordPress site performance
The Speed Optimizer plugin optimizes images enables caching, and improves front-end performance. It’s a great all-in-one tool for boosting your site’s speed and efficiency.
As a result of your site performing better in terms of speed, it consumes less server CPU and RAM resources. Hence, it is less likely to overload the server and encounter a 503 error.
SiteGround CDN
Another important aspect of web application optimization for 503 error resolution is enabling a CDN service for your site. A CDN distributes your content across multiple servers worldwide, reducing the load on your main server and speeding up content delivery to users.
Moreover, SiteGround CDN allows you to activate an Under Attack Mode to block malicious requests during a DDoS attack or flood. t also includes a Keep Site Online feature that keeps the site visible while your server is unavailable. Neat, right?
Focusing on these areas can significantly improve your site’s performance and reduce the likelihood of encountering a 503 error. For more details, check out our in-depth guide on How to improve website performance.
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Monitor Traffic and Resource Usage
To ensure you are on top of the 503 Service Unavailable error, closely monitoring your traffic and resource usage is of utmost importance. You should pay attention to any abnormal traffic spikes, as this can tip you on possible availability issues.
A great tool to monitor the traffic to your site is Google Analytics. This free service provides a powerful graphical interface of your website traffic. It also includes user behavior, visitor location, traffic spikes, user sessions, and page load times.
Moreover, Google Analytics helps you identify periods of high traffic that may have overwhelmed your server. All that information can prove invaluable when troubleshooting a 503 Service Unavailable error
SiteGround customers can also monitor traffic via their Site Tools > Statistics > Traffic tool. This tool gives an overall understanding of your website visitor stats for the current month.
Scrolling further down the Traffic page, you can also see your Bandwidth usage for the current month. That allows you to identify periods of high resource demand.
In case you’ve noticed any unusual spikes in traffic and resource usage, you may need to proceed with the next solution to get to the bottom of the issue.
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Contact Hosting Support
If you are unable to resolve the issue on your own, contact your hosting provider’s support team. They can provide detailed insights and assist in diagnosing and fixing the problem.
Hosting support teams have access to advanced diagnostic tools and can offer specific recommendations based on your hosting environment.
For more information on how to reach SiteGround’s support team, refer to the “Contact our Support Team” article.
As an example, the Support Team can provide you with a more in-depth analysis of HTTP requests or slow MySQL queries and more.
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Consider Upgrading Your Hosting Plan
If your website frequently encounters high traffic, consider upgrading to a higher-tier hosting plan. This will give your website more resources.
Shared hosting can be limited in terms of CPU, memory, and bandwidth. Thus, upgrading to a plan with more resources can help manage higher traffic volumes more efficiently.
For example, if you are on a StartUp plan at SiteGround, you can consider upgrading to a higher one. A tier-up offers more resources, like GrowBig or GoGeek plans.
For Cloud servers, you can enable SiteGround’s Autoscale Service. Auto-scaling options help your server to handle traffic spikes more efficiently. The service allows your server resources (CPU and RAM) to adjust automatically based on current demand.
That helps ensure your website remains accessible even during traffic surges.
What Causes a 503 Error?
To understand the HTTP 503 error meaning better, it’s important to examine what may be the cause of it.
In this section, we’ll go deeper into the possible reasons for an HTTP status 503, so keep reading.
Server Overload
High traffic spikes or insufficient server resources can overwhelm the server, leading to a 503 error. When too many users try to access the website simultaneously, the server may run out of available resources.
Let’s say you are running a seasonal campaign on your website. The campaign is quite successful, which results in high traffic generated by visitors trying to reach your website. However, the resources available on your web server are insufficient for such a high load. Hence, the server is overloaded and responds with HTTP error 503.
Thus, handling the requests may be difficult, resulting in a 503 Service Temporary Unavailable
Maintenance or Downtime
Web server maintenance is essential for smooth and stable service operations. It may include updates, optimization, or security patches. Such events are usually scheduled during low-traffic hours to minimize the impact on active websites.
When under maintenance, servers may be temporarily taken offline for maintenance activities. During these periods, the server is intentionally made unavailable to perform necessary updates or repairs. This often may result in a 503 response when a user tries to access your website.
Distributed Denial of Service (DDoS) attacks
A 503 error also occurs with Distributed Denial of Service (DDoS) attacks. In essence, the attacker floods the server with requests to overwhelm its resources, making it difficult for legitimate users to access the website.
Consequently, the server may run out of resources (like CPU and memory) and return a 503 Service Unavailable error. That response indicates that it is temporarily unable to process any more requests.
Incorrect Server Configuration
Incorrect server settings can lead to resource allocation problems or other issues that cause a 503 error. Misconfigured PHP settings, improper web server directives, and faulty load balancer configurations can all contribute to the server being unable to handle incoming requests.
Optimizing and correctly setting up server configurations is crucial for maintaining server availability and performance. Regular audits and updates to configuration files can help prevent these types of issues.
Faulty firewall configuration
Faulty firewall configurations or a blocked IP address can also disrupt access to your site with a 503 Service Unavailable. Such blocks may generally occur due to server-side firewall restrictions or application-level security measures.
For example:
Server-Side Locks
- Overly restrictive firewall settings may inadvertently block legitimate IP addresses.
- Exceeding the allowed number of requests per minute can temporarily block your IP (Rate Limiting).
- Due to geolocation blocking techniques, access from certain geographic regions may be restricted based on IP addresses.
- To protect the server, DDoS Protection may block IP addresses identified as part of a DDoS attack.
- Your IP may be on a blacklist due to previous malicious activity, affecting access to the site.
Security Plugins Locks
Security plugins are essential software for website protection. However, as much as they help, they can sometimes disrupt operations.
These are just a few examples that can result in a 503 error:
- Multiple unsuccessful login attempts can trigger security measures that block your IP.
- Actions flagged as suspicious, like rapid page requests, can lead to an IP block.
As you can see, a 503 error may be the output in any of the above scenarios. Hence, it is important to consider this cause during your investigation.
Weak Application Optimization
If your website isn’t well optimized, you’ll likely face a range of issues that can seriously impact its performance and user experience. Additionally, poor optimization can strain your server resources.
That makes your site more prone to errors like the 503 Service Unavailable error, especially during traffic spikes.
The key aspects of application optimization you should focus on to prevent a 503 error are as follows:
- Minimize the usage of resource-intensive plugins or scripts. Plugins that perform complex calculations or make numerous database queries can significantly slow down the server.
- Refrain from using poorly coded plugins. Such plugins tend to be inefficient or buggy, causing performance issues that can lead to a 503 error.
- Inefficient and unoptimized code can affect your website’s overall operations. This increases the chances of memory leaks and adds load on the server, consuming its resources.
- Database issues like large size, unoptimized, or slow MySQL queries can cause a 503 error. Overly large databases that are not regularly cleaned or optimized can slow down server performance, causing a response code 503.
- Lack of caching mechanisms implementations or poor cache management can result in repeated processing of the same data, increasing the server’s load.
- Heavy media files, such as large images or videos with no compression, consume significant bandwidth and processing power. A server’s inability to serve such files can result in a 503 error.
That is why application optimization is integral to website efficiency and performance.
Third-party Dependencies
Dependencies on external services (e.g., APIs, payment gateways) that are experiencing downtime can result in a 503 error. If your website relies on third-party services for critical functionality, any disruption in those services can cause your site to become temporarily unavailable.
Conclusion
Understanding what a 503 Service Unavailable error is, its causes, and how to fix it is important for maintaining a reliable and accessible website. When you Identify the root causes, whether it be
- Server overload,
- Ongoing maintenance,
- Poor application optimization,
- Third-party dependencies
or other issues, you can take appropriate steps to resolve the error and prevent it from recurring. Regular monitoring, optimization, and communication with your hosting provider are key to ensuring your website remains up and running smoothly.