Autoconfiguration support for Hazelcast IMDG & Jet

[neilstevenson]

Hazelcast consists of four options - an In-Memory Data Grid client and server, and a Jet client and server.

IMDG server works ideally. If there is an hazelcast.xml file then a server HazelcastInstance bean is constructed.

IMDG client is being improved by #7469. Ideally there is a hazelcast-client.xml file then a client HazelcastInstance bean is constructed.

This could be extended to include Jet

If there is a hazelcast.xml file and Jet classes, then a server JetInstance bean can be constructed and a server HazelcastInstance bean taken from inside Jet.

If there is a hazelcast-client.xml file and Jet classes, then a client JetInstance bean can be constructed and a client HazelcastInstance bean taken from inside Jet.

Sample project https://github.com/neilstevenson/spring-boot-autoconfigure-test shows how they are currently built using Spring Boot 1.5.2.
Ideally, all the MyConfiguration classes can be removed in favour of autoconfiguration.

[neilstevenson]

The end goal here should be at most one HazelcastInstance bean and at most one JetInstance bean

Three rules might cover it:

1. If Jet classes exist, build a Jet client if there is a hazelcast-client.xml file or build a Jet server if there is a hazelcast.xml file.

2. If the JetInstance exists, the HazelcastInstance can be extracted from it.
   When the JetInstance is a Jet client, the embedded IMDGInstance is always an IMDG client.
   When the JetInstance is a Jet server, the embedded IMDGInstance is always an IMDG server.

3. In no Jet classes are found, build a Imdg client if there is a hazelcast-client.xml file or build a Imdg server if there is a hazelcast.xml file.

[philwebb]

See also #7469

[vpavic]

IMO Spring Boot should not jump into this just yet as Hazelcast Jet is still a fresh project standing at version 0.3.1 ATM.

Project's milestones page offers some insight, with 0.4 already introducing a significant change by shading Hazelcasts JARs (both server and client) into Jet itself (see hazelcast/hazelcast-jet#367). I guess more changes like that are likely until the project reaches a stable 1.0 release.

Other than that, Hazelcast Jet seems to target a similar space as Spring Cloud Data Flow which makes me wonder if Spring Boot is natural place for Jet integration (also see the list of Jet's artifacts).

[snicoll]

@vpavic thank you for your feedback, much appreciated. I was about to write the same thing but without all those references!

@philwebb 2.0.0.M1 isn't the right milestone for this. We absolutely need support for the hazelcast-client and @vpavic did most of the work already anyway. We can revisit our auto-config later, even in a future release.

[neilstevenson]

I'll have a go at fixing this myself