503 Service Unavailable Error

Introduction

Running into errors can be intimidating. However, mist errors give a clue on what is the reason behind them, which can give you some direction for troubleshooting, and how to fix them.

The 503 Service Unavailable error unfortunately doesn't give much information to go on.

What is 503 Service Unavailable Error?

The 503 Service Unavailable error signifies that your website can't be reached at the moment because the server in question is too busy or under maintenance or something else due to which server is unavailable.

One of the worst features of this error is that it barely gives you any information to go on. Most of the time only detail it shows is "Service temporarily unavailable".

In this article, we will try to cover what is 503 error and how it typically manifests.

503 Service Unavailable Error Variations

Different Browser or Web server has their own way and language of showing an error. The same goes for the 503 error. There are a lot of ways in which a 503 error can show up. However, every variation has a common element that is 503 code, making it easier for you to identify.

Here is the snapshot of 503 error code in Twitter.

Regardless, still you can try following things-

1. Retry loading the URL.
2. Restart your router and modem and then your computer and DNS, if you are facing "Service Unavailable DNS failure error".
3. Contact website directly for help.
4. Since the 503 Service Unavailable error is a common error message on very popular websites when a huge increase in traffic by visitors is overwhelming the servers, simply waiting it out is often your best move.

Fixes of 503 Error for Different Platforms

The following section covers potential Causes and Fixes for 503 error in various platforms.

1. Websites
2. Varnish
3. Wordpress
4. Magento
5. Litespeed
6. IIS
7. Webhook

After each step, take a moment to go back to the website and see if the 503 error is gone.

If you are still facing the same error continue to the next step.

Websites

503 Service Unavailable is one of the most haunting website errors. The site will began to slow down or if the traffic exceeds the limit, the site might become unresponsive. Today, we'll see the various solutions we have considered and how you can fix this error.

S no.	Causes	Fixes
1	Inadequate server resources	Using custom tools, monitor the resource usage for various time periods and tweak the allocation accordingly
2	Web server misconfiguration	Perform fine-tuning of the web server configuration, along with MySQL and PHP Settings.
3	High web traffic due to attacks	Monitoring resource usage can help to detect and fix faulty URL that is being used for attack
4	Buggy applications or server software	Secure Docker machine with a custom firewall used for cloud servers.

Refer How to Fix 503 error in Wordpress for step by step guide on ways to fix 503 error.

Varnish

Varnish is an HTTP accelerator that improves web performance and reduces server load. If your website caches content with Varnish cache, then you might have come across Varnish cache server error 503 Service Unavailable. Checkout top Causes and Fixes for 503 error code

S no.	Causes	Fixes
1	Too many requests	Check whether ports, HTTP Service, original server etc. are operating correctly. Make sure Apache listens to the port 8080
2	Timeouts	a. Disable KeepAlive b. Add appropriate values for .connect_timeout and .first_byte_timeout
3	Length of cache tags	a. Increase default value of http_resp_hdr_len parameter b. Increase default response size http_resp_size.

Refer How to Fix 503 error in Varnish for step by step guide on ways to fix 503 error.

Wordpress

Since, you can never be sure in one go what caused 503 error in your wordpress site. You need to troubleshoot methodically. The following five pointers cover a potential fix for a cause of 503 error.

S no.	Causes	Fixes
1	Plugin compatibility issue	Temporarily deactivate your wordpress plugins
2	Themes compatibility issues	Try reinstalling the theme or revert back to the most recent backup
3	CDN Issues	Temporarily disable CDN
4	Wordpress Heartbeat API	Temporarily disable Heartbeat API
5	Server Overloading	Increase your server resources

Refer How to Fix 503 error in Wordpress for step by step guide on ways to fix 503 error.

Magento

Magento users normally see Magento 503 service unavailable error when trying to access the admin or storefront in a browser. Let's discuss this error in detail, it's Causes and Fixes.

S no.	Causes	Fixes
1	maintenance.flag	Disable maintenance mode. a. Delete maintenance.flag in Magento root folder in Magento 1.x b. Delete maintenance.flag in Magento root folder/var in Magento 2.x

Refer How to Fix 503 error in Magento for step by step guide on ways to fix 503 error.

Litespeed

Generally, Litespeed shows 503 Service Unavailable error when it is unable to handle the HTTP Requests. This might happen due to a temporary overloading or maintenance of the server. Checkout the Causes and Fixes for 503 error in Litespeed.

S no.	Causes	Fixes
1	Memory constraints	Increase memory limit values and for the PHP memory limits, edit php.ini file of the domain.
2	Bad Litespeed configuration	Increase process timeout in LFD Configuration and increase user process limits.
3	Using multiple cache modules	Ensure there is always one cache module on the server.
4	CSF/ LFD killing PHP	Disable PHP modules like loncube, Suhosin, Zenguard by commenting out entry from php.ini file.
5	Disk full	Ensure enough free disk space in server partitions

Refer How to Fix 503 error in Litespeed for step by step guide on ways to fix 503 error.

IIS

We often see errors in Windows server. But we are not sure how to start troubleshooting. Today, we are discussing few Causes and Fixes of HTTP Error 503 for Windows server.

S no.	Causes	Fixes
1	Application pool of the corresponding Web application stopped working	Restarting application pool
2	Misconfiguration in the application pool or site settings	Fix the settings of application pool like enabling the relevant protocol.
3	Issues related to the user identity of application pool	Check account settings and password of the identity, in case of mismatch update the settings
4	Application pool running out of RAM or other server resources	Assign dedicated application pool for that domain

Refer How to Fix 503 error in IIS for step by step guide on ways to fix 503 error.

Webhook

Webhooks allow you to receive real-time notifications. Quite often 503 Service Unavailable error pops up while using the applications in real servers. Let's have a look at top Causes and Fixes for 503 error code.

S no.	Causes	Fixes
1	Server connectivity issue	Fix error causing server unreachable. Some of the common reasons are server firewall blocks, network errors etc.
2	Host down	Properly reboot all the systems. Make sure webserver is up and running.
3	Application code or script bug	Consult developer to fix bug in the code that is causing 503 error.

Refer How to Fix 503 error in Webhook for step by step guide on ways to fix 503 error.