Magento Soap API working locally but not remotely - magento

Question

I have created a custom API for Magento Enterprise 1.11. Calling the API through Soap v1 works fine on my local dev environment, however I am unable to make calls from my local environment to the remote environment.
Using PHP interactive shell on my localdev:
php > $client = new SoapClient(WSDL_URI,array('trace'=>1));
php > $client->login(API_USER,API_KEY);
php > var_dump($client->__getLastResponse());
string(538) "<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns1="urn:Magento" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/" SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"><SOAP-ENV:Body><ns1:loginResponse><loginReturn xsi:type="xsd:string">f0eec73e49665aaf9cc4a6644fba5dc6</loginReturn></ns1:loginResponse></SOAP-ENV:Body></SOAP-ENV:Envelope>
I have been able to do this successfully from the localhost, as well as between two local VMs running on my dev machine. I can also access the methods of my custom API without issue.
However, when I try to make a soap client to my remote test environment, I am able to create the client, but the call to $client->login(), or any subsequent call results in the following:
php > $client = new SoapClient(REMOTE_WSDL_URI,array('trace'=>1));
php > $client->login(API_USER,API_KEY);
PHP Warning: Uncaught SoapFault exception: [WSDL] SOAP-ERROR: Parsing WSDL: Couldn't load from 'http://REMOTE_HOST/index.php/api/index/index/wsdl/1/' : failed to load external entity "http://REMOTE_HOST/index.php/api/index/index/wsdl/1/" in php shell code:1
Stack trace:
#0 php shell code(1): SoapClient->__call('login', Array)
#1 php shell code(1): SoapClient->login(API_USER, API_KEY)
#2 {main}
php > var_dump($client->__getLastRequestHeaders());
string(255) "POST /index.php/api/index/index/ HTTP/1.1
Host: REMOTE_HOST
Connection: Keep-Alive
User-Agent: PHP-SOAP/5.3.18-1~dotdeb.0
Content-Type: text/xml; charset=utf-8
SOAPAction: "urn:Mage_Api_Model_Server_HandlerAction"
Content-Length: 550
php > var_dump($client->__getLastResponseHeaders());
string(840) "HTTP/1.1 500 Internal Service Error
Date: Mon, 11 Feb 2013 19:06:56 GMT
Server: Apache/2.2.16 (Debian)
X-Powered-By: PHP/5.3.19-1~dotdeb.0
Set-Cookie: PHPSESSID=7uqrcmiv96hroubnb1uu7c7cm6; expires=Wed, 13-Feb-2013 01:06:56 GMT; path=/; domain=.REMOTE_HOST; HttpOnly
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Set-Cookie: CUSTOMER=deleted; expires=Thu, 01-Jan-1970 00:00:01 GMT; path=/; domain=.REMOTE_HOST; httponly
Set-Cookie: CUSTOMER_INFO=deleted; expires=Thu, 01-Jan-1970 00:00:01 GMT; path=/; domain=.REMOTE_HOST; httponly
Set-Cookie: CUSTOMER_AUTH=deleted; expires=Thu, 01-Jan-1970 00:00:01 GMT; path=/; domain=.REMOTE_HOST; httponly
Content-Length: 468
Vary: Accept-Encoding
Connection: close
Content-Type: text/xml; charset=utf-8
php > var_dump($client->__getLastResponse());
string(468) "<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"><SOAP-ENV:Body><SOAP-ENV:Fault><faultcode>WSDL</faultcode><faultstring>SOAP-ERROR: Parsing WSDL: Couldn't load from 'http://REMOTE_HOST/index.php/api/index/index/wsdl/1/' : failed to load external entity "http://REMOTE_HOST/index.php/api/index/index/wsdl/1/"
</faultstring></SOAP-ENV:Fault></SOAP-ENV:Body></SOAP-ENV:Envelope>
When I hit //REMOTE_HOST/index.php/api/?wsdl I get the standard Magento WSDL.
The two environments are 99.99% identical:
Server version: Apache/2.2.16 (Debian) (both local dev and remote)
PHP 5.3.18 (local dev) 5.3.19 (remote host)
Apache/PHP configurations are the same.
Code base is identical
I have scoured the intewebs for clues, including:
http://www.magentocommerce.com/boards/viewthread/56528/
http://www.magentocommerce.com/wiki/5_-_modules_and_development/web_services/overriding_an_existing_api_class_with_additional_functionality#wsdl
Unable to connect to Magento SOAP API v2 due to "failed to load external entity"
Magento API SOAP-ERROR: Parsing WSDL: Couldn't load from '[url]/index.php/api/index/index/?wsdl=1' : Couldn't find end of Start Tag part line 56
http://www.magentocommerce.com/api/soap/introduction.html
I've tried the "Content-Length" header fix mentioned in the sedond-to-last link, and just about everything else I could think of... Stumped.

Answer 1

While you can load the WSDL URL (http://REMOTE_HOST/index.php/api/index/index/wsdl/1/) from your computer, your remote server can't contact itself via its REMOTE_HOST.
PHP's SoapServer object (used by Magento's implementation) needs to contact the WSDL to know which methods are exposed.
For reasons I've never been able to figure out, it's a common network configuration for a server to not have access to it's own DNS entries. Connect to your server via SSH and try running the following
curl http://REMOTE_HOST/index.php/api/index/index/wsdl/1/
My guess is you'll get a network timeout or a REMOTE_HOST unknown error. Fix your configuration so your server can access itself, and everything should start working.

Answer 2

You could try changing host DNS nameservers perhaps.
vim /etc/resolv.conf to add Google's 8.8.8.8, 8.8.4.4