Elastic stack upgrade to 7.1 or 7.2

[kamatbipin17 (Bipin Kamat)]

I need some inputs on upgrading ES stack specifically with my project and let me know if you can help anyways

we have search platform ( Elastic search and Kibana) on 6.1.3 version . WE have around 125 million documents and few other indices on ES . We intend to upgrade to latest 7.x version in coming months . We want to know what is the best path to upgrade to 7.1 or 7.2 from 6.1.3 without encountering any issues due to upgrade?

The video ( https://www.elastic.co/webinars/upgrading-your-elastic-stack) talks about upgrade path for 6.7 as either
a) 6.7 -> 6.8 -> 7.1 or
b) 6.7 ->7.0->7.1

Does it mean upgrade from version 6.7 or below (6.1.3 in our case) to 7.1 or 7.2 is not recommended ?

Kindly provide the inputs on best practices and also possible issues (if any) we may encounter during direct upgrade from 6.1.3 to 7.1 or 7.2 .

[Denis_Lamanov (Denys Lamanov)]

Unwanted Upgrade ElasticSearch version

To be clear, all downgrades are forbidden. Sometimes a downgrade will appear to work (possibly silently losing data) and sometimes they'll fail as reported here, but downgrading to any earlier version is unsupported. This is even true for patch releases like trying to downgrade from 7.1.1 to 7.1.0. This is not completely true. You can upgrade directly from any 6.y version to any 7.x version (for x ≥ 1) via a full cluster restart. If you want to perform a rolling upgrade you can only do this f…