Maven : Return code is: 503 , ReasonPhrase:Service Unavailable

 [ERROR] Plugin org.apache.maven.plugins:maven-clean-plugin:2.5 or one of its dependencies could not be resolved: Failed to read artifact descriptor for o rg.apache.maven.plugins:maven-clean-plugin:jar:2.5: Could not transfer artifact org.apache.maven.plugins:maven-clean-plugin:pom:2.5 from/to internal (http://localhost:8081/artifactory/libs-release-local): Failed to transfer file: http://localhost:8081/artifactory/libs-release-local/org/apache/maven/plugins/maven-clean-plugin/2.5/maven-clean-plugin-2.5.pom. Return code is: 503 , ReasonPhrase:Service Unavailable. -> [Help 1]  

settings.xml

 <settings xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0" xsi:schemalocation="http://maven.apache.org/POM/4.0.0   
            http://maven.apache.org/xsd/settings-1.0.0.xsd">  
   
 <proxies>  
    <proxy>  
    <id>optional</id>  
    <active>true</active>  
    <protocol>http</protocol>  
     <username>proxy_user</username>  
    <password>proxy_password</password>  
    <host>proxy_name</host>  
    <port>8080</port>  
    </proxy>  
 </proxies>    
   
 <mirrors>  
   <mirror>  
    <id>internal</id>  
    <url>http://localhost:8081/artifactory/libs-release-local</url>  
    <mirrorof>*</mirrorof>  
   </mirror>  
 </mirrors>  
 </settings>   

The problem is with your proxy settings. The current settings will cause all requests to localhost to go through the proxy which will not be able to connect with localhost and hence returns a 503.

To solve this issue add the following to the proxy settings in the settings.xml file:

 <nonproxyhosts>localhost</nonproxyhosts>