Elasticsearch transform role backward compatibility

[Mohammad_Mousavi]

Hi, I have a 3 nodes elasticsearch cluster with 7.4.2 version.
It's look like this version does not support "transform role". I see in elasticsearch version 7.10.1 logs that a module called "transform" is loaded in starting elasticsearch service. It's look like it does not exist in version 7.4.2 .
This is version 7.4.2 with node role transfoem in config file:

org.elasticsearch.bootstrap.StartupException: java.lang.IllegalArgumentException: unknown setting [node.roles] please check that any required plugins are installed, or check the breaking changes documentation for removed settings

I've setup a 4th node with version 7.10.1 and join this new node to cluster with transform role ( I know it's stupid but I just wanted to test )
I've tested kibana version 7.10.1 and it can not connect to elasticsearch version 7.4.2 .
The _transform api also does not work properly.
Upgrading my cluster will cost me a lost. It will be the last option.
Is there any way to use "transform role" in elasticsearch and kibana version 7.4.2 ??
I don't know , maybe with install some plugin or modules or what ever.
Sorry for my poor English.
Thanx a lot.

[Hendrik_Muhs]

A cluster must always be formed from the same version, if you want to add a new node to an existing cluster it must be the same minor (you can add a node with a newer patch revision (the last digit, e.g. 7.4.3 - if 7.4.3 would exist).

The only valid case for a so called mixed version cluster is during a rolling upgrade. That brings me to:

Upgrading my cluster will cost me a lost.

Upgrades can be done in a rolling fashion without downtime, see Rolling upgrade | Elasticsearch Guide [8.11] | Elastic

The problems you see with transform is just the tip of the iceberg, using a much newer kibana version with an old elasticsearch cluster is not supported.