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Amrith: Some comments regarding the scarcity of deployments, and the 
proposed approach.

We know of multiple teams that are now independently charging down and 
investing in a Trove path.  They are at various stages of deployment and 
are beyond tire-kicking. They are beginning to build dev/test 
environments, some are building commercial products, and we fully expect 
some people to be in production with Trove by the end of the year. 
Collectively, we need to start bridging and engaging these people into the 
Trove community. 

We also strongly believe that we need an evolutionary approach to moving 
Trove forward vs. the revolutionary approach that is being proposed.  Our 
deeply held view is that it is feasible and rationale to evolve Trove as 
it exists today.  We agree that there are architectural issues that have 
to be addressed.   Let's start working on addressing these issues as well 
as the current currency issues but in a evolutionary way.  The 
revolutionary approach will halt all progress and set a bad precedent, and 
we believe that it will cause people to walk away from the community and 
likely OpenStack as well. 

- Manoj



From:   Amrith Kumar <amrith.kumar at gmail.com>
To:     "OpenStack Development Mailing List (not for usage questions)" 
<openstack-dev at lists.openstack.org>
Date:   06/18/2017 06:41 AM
Subject:        [openstack-dev] [trove][all][tc] A proposal to rearchitect 
Trove



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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