Some alternatives:
- The rivers can still be used, until the version 2.0 of Elasticsearch. But it's not a long term solution.
- You can write your own solution, as said plmaheu. It's some work, but will fit your program perfectly and is recommended on the Elasticsearch blog.
- Instead of writing a log of custom code, you can send the insert/update/delete requests to Logstash, that will make them on Elasticsearch. I like this solution since Logstash will make bulks for you and handle other things that you don't want to implement by yourself.
- I heard that you can use an ETl tool like Talend, but I didn't investigated that solution since it's a paying solution.
- There is the gatherer plugin that was supposed to replace the rivers. However it has not been update since last year so it's likely that the project has been abandoned.
The two solutions recommended on the ES blog are writing your solution or using Logstash. Choose the one that fits your requirements.
Note: a lot of great solutions are currently in development to replace the rivers, the logstash-jdbc input as an example. The deprecation of the rivers is quite recent and can expect that many replacements will emerge over the next months/years.