[openstack-dev] [trove][all][tc] A proposal to rearchitect Trove

Matt Fischer matt at mattfischer.com
Mon Jun 19 20:00:13 UTC 2017


Some good thoughts in your email. I've replied to a few specific pieces
below. Overall I think it's a good start to a plan.

On Sun, Jun 18, 2017 at 5:35 AM, Amrith Kumar <amrith.kumar at gmail.com>

> 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.
> 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

This was a major concern when we deployed it and drove the architectural
decisions. I'd be glad to see it resolved or re-architected.

> - 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

+1 to this also. Trove should offer a black box DB as a Service, not
something the user sees as an instance+storage that they feel that they can

> - 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

I would add that reducing the focus on adding more and more DBs, rather
than having a few very well supported ones would help in your Trove reboot.

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

This is how we positioned Trove when it was deployed. A single node DB is
not a very cloudy solution when you have to do maintenance or lose a
hypervisor. I'd consider clusters the main use case. We discouraged anyone
from using non-clustered solutions except for trying out Trove.

> - 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

or regions

> 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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