Elasticsearch can be installed in seconds with most package managers and syncing is trivial depending on what you want to index. You can use a JDBC river for bulk indexing or rely on trigger's.
Eh, that's more for logs specifically. The "syncing story" is something that depends on your technology platform and specific situation. I adopted ES when it had rivers, but never even considered using them for syncing.
> syncing is trivial depending on what you want to index
Can you explain how you keep your Elasticsearch index consistent with your main database, in face of system failure (for example a network partition or a machine hard reboot)? This is usually the non-trivial part.