So I have a rather simple Node.js application running on a single server, using mongoDB as primary database and elasticsearch as a "replica set" with only search-relevant fields indexed in ES. I need the upgrade, because the older version conflicts with fields starting with an underscore (eg. "_id").
Is there a way to upgrade elasticsearch with little to no downtime - without falling back to the mongoDB? Also what's the proper way to backup elasticsearch in this scenario? What would be the steps to restore a backup, in case something goes wrong?
TLDR: what's the proper way to backup and then upgrade between those versions?
Since the amount of data you have currently is not that big, maybe the solution is to set up a brand new 1.7 cluster, index your data in it and then flip the switch, i.e. you make your node app you point to the new 1.7 cluster instead of the old 0.90.7 one. That should do the trick.
Note: ES 1.7 ideally requires Java 8 but also supports Java 1.7.0_55 or later, so with 1.7.0_79 you should be good to go on the Java front.