Java version conflicts in janusgraph-full distribution

[porunov]

@JanusGraph/committers @JanusGraph/maintainers I wanted to discuss Java version conflicts in janusgraph-full build.

I'm currently working on the PR to add ElasticSearch 8 support here: #3268

I bumped into the problem with janusgraph-dist tests failing for tests using ElasticSearch. After a small investigation it appears that ElasticSearch Server 8 doesn't support Java 8 or Java 11 anymore. ElasticSearch Server 8.6.0 requires Java 17, 18, or 19 (see compatibility matrix).
Notice, ElasticSearch Rest client which we are using supports Java 8. It's only the server itself requires Java 17 or higher.

Our janusgraph-dist tests are running against Java 8 and Java 11 and then produce Java 8 and Java 11 compatible builds.
Gremlin Console supports Java 8 and Java 11, but not Java 17.
JanusGraph server supports Java 8, Java 11, Java 17 (and probably more).

As for now, I decided to lock ElasticSearch 7.17.8 version in janusgraph-dist builds to be able to continue produce Java 8 and Java 11 compatible builds.
There are possible other solutions I see to this problem:

• Remove janusgraph-full distributions
• Change JanusGraph Server script a little bit by providing ELASTICSEARCH_JAVA_HOME environment variable which gets Java from ELASTICSEARCH_JAVA_HOME instead of JAVA_HOME. In such case Cassandra, JanusGraph Server, Gremlin Console will use JAVA_HOME (which is either 8 or 11) and ElasticSearch will use ELASTICSEARCH_JAVA_HOME (which is 17, 18, or 19). I guess users might be confused a little bit about ELASTICSEARCH_JAVA_HOME environment variable, but if we document it in the Installation docs then it should be good I think.
• Run janusgraph-dist builds using Java 17 only, but modify Gremlin Console a bit to introduce Java environment variable to the Gremlin Console (like GREMLIN_JAVA_HOMEor something like that). In such case Cassandra, ElasticSearch, JanusGraph Server will be running using Java 17, but users will be opening Gremlin Console using Java 8 or Java 11. Again, we will need to document it.

Maybe there are other solutions I missed, but would be good to hear your thoughts or preferences here.

[farodin91]

I'm pretty sure at the moment elasticsearch has their own Java distribution.