We are using sling servlet with POST method in our AEM6.4 application. We are receiving "504 Gateway timeout" response, due to long processing (we are connecting to external service from sling servlet) time. Could you please let me know, if there is way to fix it like changing timeout for sling servlet.
This is a timeout because the server does not send any data over some time. You should either send data during processing or rather implement this as workflow or sling job. Then you can inititate the job, and regularly check the status. No need to worry about timeouts anymore.