Questions about upgrading ES 6 -> 7

Hey,

We are planning to do an online 6->7 upgrade for our ES clusters, and we are looking into ways of rolling back safely from 7 to 6 in case something bad happens. The ES docs state that once the upgrade starts, the ES cluster will run into a backwards-compatible mode and will start using ES7 features after all nodes are fully upgraded. To get a better understanding of this, I have a few questions:

  1. Is this switch happening automatically? Would it be possible to prevent it? (via a code change, or a setting change)
  2. What would be the place in the code where this switch would happen?

Thank you,
Relu

If you need to be able to roll back to version 6 you will need to create a snapshot before you start the migration so you can revert to this. Once indices have been touched by version 7, they will no longer be readable from version 6 as Elasticsearch does not support downgrades.