Elastic upgrade hosted on GCP

Hi there,
I am pretty new to Elasticsearch and I ran into an Upgrade task that gave me some doubts.
I have a 3-nodes Cluster running Elasticsearch on Google Cloud (as a Google Click to Deploy deployment) ad I must upgrade my stack which currently is a 5.6.8 to the latest 7.6.2.
I suppose my biggest problem is reindexing, since it seems to be my only valuable data on the cluster.
I was scouting on elastic.co documentation and I was wondering which was the best way to upgrande and reindex between :
a) Upgrade to 6.8, install Kibana and run Kibana Agest to automatically reindex to 7.6.2, upgrade then to 7.6.2
b) Set up a new 7.6.2 cluster and just reindex from remote

I was going with option b) but I have some doubts since I read that the reindex operation is manual and I have 200+ indexes with 1000+ documents and it scared me a little.
If there are other alternatives I am open to discussion :wink:
Thanks in advance

Either will work, it's what you are comfy with that is important.

That's a really high index to document ratio. You may want to revisit that approach and merge some of these with a reindex?

Ok Thanks.
When reindexing from remote, is there a way to do it automatically or do I have to make a single API call for each index I want to restore?
I am referring to https://www.elastic.co/guide/en/elasticsearch/reference/7.6/reindex-upgrade-remote.html as a guide.

You can use wildcards, but yes, at the moment it's manual. You could do some simple scripting to automate each call though.

That's what I thought thanks.
After reindexing I expect to have all my old indices and documents back where I left them, with a newer version of ES right? I suppose i shouldn't worry about restoring some indices from a backup after that.

You should have a backup anyway, it's good habit and risk mitigation.
But yes, pending any problems that may crop up, that's the goal :slight_smile:

Yes sure. I was asking because I already have a backup and I tried to restore it from Google Cloud Storage( with the repository-gcs plugin) after doing an upgrade to a single node from 5.6 to 6.8 but I noticed that a lot of indices where missing even if the process got no error. I guess this is due to the fact that the different versions of ES require a reindex before upgrading, am I right?

Some versions do, yes. https://www.elastic.co/guide/en/elasticsearch/reference/7.6/reindex-upgrade.html has more on that.

Is there a way to remove a backed up index manually from the repo? I did a snapshot on GCS but I can't find the index with the id I have, I don't understand how indices are backed up on Google Cloud Storage.
Thanks in advance

You would need to delete the snapshot itself, manually removing files is likely to cause other issues.