Hypertext Transfer Protocol or HTTP  503 Service Unavaiable server error response code indicates that the server is not ready to handle the request. Also HTTPS protocol will use the same code for the same reason. In this tutorial we will examine the 503 error code causes, client and server side solutions.

503 Expressions

HTTP 503 code can be expressed a little bit differently for different web servers. There are different web servers like Apache, IIS, lighttpd, Nginx etc.

503 Service Unavailable

503 Service Temporarily Unavailable

Http/1.1 Service Unavailable

HTTP Server Error 503

Service Unavailable - DNS Failure

503 Error

HTTP 503

HTTP Error 503

Error 503 Service Unavailable

Reasons

This error code simply means Service Unavailable which means server can not handle and response to the request properly. Here the list of the HTTP 503 error causes.

• There is an update on the web server
• There is a bug in the server software
• There is a bug in the web application
• The request is an comply with the request filter
• There is a lot of request to the server which can not handled in the same time
• There is regular DDOS attack to the web server
• Client cache is poisoned with improper data

Client or Browser Solutions

Actually the error is mainly related with the server side but there may be some steps on the client side to try.

• Using different browser where some browser can send improper request.
• Clearing browser cache where poisoned data can be retrieved from cache

Server Side Solutions

The error is mainly related with the server side. We can do a lot of things to solve503 error. In some cases we may require to complete multiple of the following solutions.

• Restart the web server service
• Reload the web application
• Examine the server logs
• Check DNS server
• Increase concurrent request limit of web server
• Increase bandwidth of network connection
• Check the application logic related with URL

Programming Language and Frameworks Code References

In some cases we may want to sent 503 code to the client HTTP request. This can be done easily with the all ready defined codes in the programming languages and frameworks.

Rails HTTP 503 Status Code

:service_unavailable

Go HTTP 503 Status Code

http.StatusServiceUnavailable

Symfony HTTP 503 Status Code

Response::HTTP_SERVICE_UNAVAILABLE

Python2 HTTP 503 Status Code

httplib.SERVICE_UNAVAILABLE

Python3 HTTP 503 Status Code

http.client.SERVICE_UNAVAILABLE

Python 3.5+ HTTP 503 Status Code

http.HTTPStatus.SERVICE_UNAVAILABLE

PHP HTTP 503 Status Code

StatusCodes::httpHeaderFor(503)