Use node.roles instead of deprecated setting for Elasticsearch 7.9+

[jmlrt]

This role use node.master and node.data settings to define node roles.
However these settings have beed deprecated in favor of node.roles setting in 7.9 (elastic/elasticsearch#54998).

[jmlrt]

related to elastic/elasticsearch#66409

[Bernhard-Fluehmann]

@jmlrt It seems that up to now node role settings are done in es_conf and node. is only mentioned in README.md
The easiest way would be to just update the readme files to use node.roles, but this would then not work on older versions.
Another, more sophisticated solution would be to create a new variable called node_roles. This would allow to properly implement version specific configuration in template and use the variable to build legacy config for older versions.
readme could easily be adopted to the new var.
What do you think about?

[abraxxa]

I prefer the flexibility of es_conf and would just remove the now incorrect parts in README.md.

[Bernhard-Fluehmann]

Makes sense

[bndabbs]

I've also handled role assignments with inventory groups, which is useful for doing lookups to populate things like the seed hosts.

Something like this:

[elasticsearch:children]
es_master
es_data
es_ingest

[es_master]
elasticsearch0[1:3]

[es_data]
elasticsearch0[1:4]

[es_ingest]
elasticsearch0[1:4]

[elasticsearch:vars]
# Disable all node roles by default
node_master=false
node_data=false
node_ingest=false

[es_master:vars]
node_master=true

[es_data:vars]
node_data=true

[es_ingest:vars]
node_ingest=true

[Bernhard-Fluehmann]

I am doing it in a similar way. But instead of node_... I am using a variable which reflects the new config method.

es_node_roles:
- master
- data
- ingest

The benefits of the new method is that it is clearly visible what is enabled or not and therefore no disabling needed anymore.

[botelastic]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[jmlrt]

still valid

[botelastic]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[jmlrt]

still valid