6.7 docker build_type breaking 6.6 client

[brackxm]

a 6.6 high level rest client cannot parse the MainResponse from a 6.7 server
due to the new docker build_type (#39378 )
previously a docker distribution was returning the tar type

this prevents 6.6 -> 6.7 upgrades with server before client
client before server upgrades are also not possible due to other 7.0 forward compatibility changes in 6.7
this leaves no 6.6 -> 6.7 or 7 upgrade path

[elasticmachine]

Pinging @elastic/es-core-features

[javanna]

Thanks for reporting this @brackxm , this is indeed a problem. We will discuss possible solutions with the team.

[javanna]

cc @hub-cap I marked this team-discuss .

[jasontedor]

Thanks for reporting this @brackxm and sorry for the issue. As @javanna mentions, we will consider some options and see what we can come up with.

[hub-cap]

Hi @brackxm, Thank you for pointing this out. This did not get caught due to some testing inefficiencies, which I will be hopefully addressing soon. But in the meantime I plan on going thru all of our response parsers manually to see if they suffer from this issue potentially, and if so, correct them such they will not hamper compatibility between versions. #40705 is the first which addresses the parsing problem of this class.

[iremmats]

Would there be any risc overriding the /usr/share/elasticsearch/bin/elasticsearch-env file and at the bottom of it change ES_DISTRIBUTION_TYPE=docker to ES_DISTRIBUTION_TYPE=tar? I just tried this and it made it possible to connect a 6.7.0 node to a 6.6.2 cluster.