Hi devs,
I've been spiking a new approach to our YAML modelling for java objects.
The root problem I want to solve is to that it's tedious, inconsistent,
and poorly documented how YAML should map on to the Java items. Every
new place we want to do this we use ad hoc code. This is an obstacle to
writing new java items which can easily be configured in YAML by any
Brooklyn user.
The idea of the solution is to have a schema for mapping Java <-> YAML
so you can simply annotate the Java classes and the job's done. You get
a working schema for reading from YAML without having to think about
it. The thinking is that this lets us make many more things expressible
in YAML, including:
* effectors defined as sequences of tasks
* common predicates (as has been discussed in #282 [1] and the mailing list)
* more sensor feeds, policies, etc
I've built a prototype called "YOML" (YAML Object Mapping Language) and
opened a PR for it [2].
As it stands it supports reading and writing (so we could improve our
persistence model and be able to output reusable plans from the current
state of the world -- though I've not worked on those), and it's
designed to be very flexible, optimizing for the experience of the human
reading and writing it.
It also has hooks for reflecting about itself -- meaning we could
generate documentation and code completion proposals with explanations
for everything that is YOML'd (though again not implemented).
It's integrated with the new BrooklynTypeRegistry (code which replaces
the old fixed-type-category catalog, allowing arbitrary types and
aliases; it's used currently, but not persisted, and we're not taking
advantage of it yet; we could also use this to restrict who can use
which types) and has a TypePlanTransformer so we can use it in specific
places. You can use anywhere the YAML DSL is supported by saying
`$brooklyn:object-yoml: ...`, and it's hooked in specially in one place,
under brooklyn.initializers if you supply a map (previously only a list
was allowed), with some sensor/effector tests at [3], in short allowing:
- type: org.apache.brooklyn.entity.software.base.EmptySoftwareProcess
brooklyn.initializers:
echo-hi-name-from-config:
type: ssh-effector
command: echo hi ${NAME}
env:
NAME: $brooklyn:config("name")
date:
type: ssh-sensor
command: date
period: 100ms
brooklyn.config:
name: bob
A detailed write-up is at [4].
I could do an online brown-bag session next week if folks are interested.
Best
Alex
[1] https://github.com/apache/brooklyn-server/pull/282
[2] https://github.com/apache/brooklyn-server/pull/363
[3]
https://github.com/ahgittin/brooklyn-server/blob/yoml/camp/camp-brooklyn/src/test/java/org/apache/brooklyn/camp/yoml/YomlTypeRegistryEntityInitializersTest.java
[4]
https://github.com/ahgittin/brooklyn-server/blob/yoml/utils/common/src/main/java/org/apache/brooklyn/util/yoml/sketch.md
