Some services/components are related or have dependencies on other
services and components.As an example, in HDP, the Hive service depends
on HBase and Zookeeper.In Savanna, there is no way to express this
relationship.If a user wanted to deploy Hive, they would need to know to
install both HBase and Zookeeper a priori.Also, because the list of
service components(node processes) that is provided to a user to be used
in node groups is a flat list, only the component name gives any
indication as to what service the components belong to.Because of this,
it will likely be difficult for the user to understand exactly what
components are required to be installed for a given
service(s).Currently, the HDP stack consists of approximately 25 service
components.
A primary reason that it isn't currently possible to express
service/component relationships is that topology is defined from the
bottom up.This means that a user first selects components and assigns
them to a node template.The users first interaction is with components,
not services.Currently, the user will not know if a given topology is
valid until an attempt is made to deploy a cluster and validate is
called on the plugin.At this point, if the topology were invalid, the
user would need to go back and create new node and cluster templates.
One way to express service relationships would be to define topology top
down, with the user first selecting services.After selecting services,
the related service components could be listed and the required
components could be noted. This approach is a significant change to how
Savanna currently works, has not been thoroughly thought through and and
is only meant to promote conversation on the matter.
After making new services available from the HDP plugin, it is clear
that defining a desired (valid) topology will be very difficult and
error prone with the current savanna architecture.I look forward to
discussing solutions to this matter with the community.
-John
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