Splunk has various SDKs for different languages and platforms. We are going to talk about them shortly and won't cover deep application development. Our goal is to get the result as rapidly as possible and using few application development skills. We can always turn to custom development, and our goal is to get quick insights as soon as possible.
There is a nice portal—https://splunkbase.splunk.com—where you can find hundreds of published applications. Extending Splunk with a SDK is not something special; it's a recommended approach to get extended functionality. This book has a chapter describing integration with MongoDB. The MongoDB integration application is taken from the splunkbase portal. We encourage you to look through published apps before starting to develop your own.