Open Stack

Trove has evolved rapidly over the past several years, since integration in
IceHouse when it only supported single instances of a few databases. Today
it supports a dozen databases including clusters and replication.

The user survey [1] indicates that while there is strong interest in the
project, there are few large production deployments that are known of (by
the development team).

Recent changes in the OpenStack community at large (company realignments,
acquisitions, layoffs) and the Trove community in particular, coupled with
a mounting burden of technical debt have prompted me to make this proposal
to re-architect Trove.

This email summarizes several of the issues that face the project, both
structurally and architecturally. This email does not claim to include a
detailed specification for what the new Trove would look like, merely the
recommendation that the community should come together and develop one so
that the project can be sustainable and useful to those who wish to use it
in the future.

TL;DR

Trove, with support for a dozen or so databases today, finds itself in a
bind because there are few developers, and a code-base with a significant
amount of technical debt.

Some architectural choices which the team made over the years have
consequences which make the project less than ideal for deployers.

Given that there are no major production deployments of Trove at present,
this provides us an opportunity to reset the project, learn from our v1 and
come up with a strong v2.

An important aspect of making this proposal work is that we seek to
eliminate the effort (planning, and coding) involved in migrating existing
Trove v1 deployments to the proposed Trove v2. Effectively, with work
beginning on Trove v2 as proposed here, Trove v1 as released with Pike will
be marked as deprecated and users will have to migrate to Trove v2 when it
becomes available.

While I would very much like to continue to support the users on Trove v1
through this transition, the simple fact is that absent community
participation this will be impossible. Furthermore, given that there are no
production deployments of Trove at this time, it seems pointless to build
that upgrade path from Trove v1 to Trove v2; it would be the proverbial
bridge from nowhere.

This (previous) statement is, I realize, contentious. There are those who
have told me that an upgrade path must be provided, and there are those who
have told me of unnamed deployments of Trove that would suffer. To this,
all I can say is that if an upgrade path is of value to you, then please
commit the development resources to participate in the community to make
that possible. But equally, preventing a v2 of Trove or delaying it will
only make the v1 that we have today less valuable.

We have learned a lot from v1, and the hope is that we can address that in
v2. Some of the more significant things that I have learned are:

- We should adopt a versioned front-end API from the very beginning; making
the REST API versioned is not a ‘v2 feature’

- A guest agent running on a tenant instance, with connectivity to a shared
management message bus is a security loophole; encrypting traffic,
per-tenant-passwords, and any other scheme is merely lipstick on a security
hole

- Reliance on Nova for compute resources is fine, but dependence on Nova VM
specific capabilities (like instance rebuild) is not; it makes things like
containers or bare-metal second class citizens

- A fair portion of what Trove does is resource orchestration; don’t
reinvent the wheel, there’s Heat for that. Admittedly, Heat wasn’t as far
along when Trove got started but that’s not the case today and we have an
opportunity to fix that now

- A similarly significant portion of what Trove does is to implement a
state-machine that will perform specific workflows involved in implementing
database specific operations. This makes the Trove taskmanager a stateful
entity. Some of the operations could take a fair amount of time. This is a
serious architectural flaw

- Tenants should not ever be able to directly interact with the underlying
storage and compute used by database instances; that should be the default
configuration, not an untested deployment alternative

- The CI should test all databases that are considered to be ‘supported’
without excessive use of resources in the gate; better code modularization
will help determine the tests which can safely be skipped in testing changes

- Clusters should be first class citizens not an afterthought, single
instance databases may be the ‘special case’, not the other way around

- The project must provide guest images (or at least complete tooling for
deployers to build these); while the project can’t distribute operating
systems and database software, the current deployment model merely impedes
adoption

- Clusters spanning OpenStack deployments are a real thing that must be
supported

This might sound harsh, that isn’t the intent. Each of these is the
consequence of one or more perfectly rational decisions. Some of those
decisions have had unintended consequences, and others were made knowing
that we would be incurring some technical debt; debt we have not had the
time or resources to address. Fixing all these is not impossible, it just
takes the dedication of resources by the community.

I do not have a complete design for what the new Trove would look like. For
example, I don’t know how we will interact with other projects (like Heat).
Many questions remain to be explored and answered.

Would it suffice to just use the existing Heat resources and build
templates around those, or will it be better to implement custom Trove
resources and then orchestrate things based on those resources?

Would Trove implement the workflows required for multi-stage database
operations by itself, or would it rely on some other project (say Mistral)
for this? Is Mistral really a workflow service, or just cron on steroids? I
don’t know the answer but I would like to find out.

While we don’t have the answers to these questions, I think this is a
conversation that we must have, one that we must decide on, and then as a
community commit the resources required to make a Trove v2 which delivers
on the mission of the project; “To provide scalable and reliable Cloud
Database as a Service provisioning functionality for both relational and
non-relational database engines, and to continue to improve its
fully-featured and extensible open source framework.”[2]

Thanks,

-amrith​


[1] https://www.openstack.org/assets/survey/April2017SurveyReport.pdf
[2] https://wiki.openstack.org/wiki/Trove#Mission_Statement
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