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From Rafael Weingärtner <>
Subject Re: Let’s discuss database upgrades
Date Sun, 03 Jan 2016 12:19:53 GMT
Sorry the delay on answering your inquiries, during this period of New
Year’s Eve I was AFK.

Thanks for the contributions of all.
I will comment your questions and suggestions as follows:

Ron, I understand your point that there are some projects that do not allow
database change in minor version releases (schema changes). We could define
that as a standard, I do not see a problem on that, as long as we have
consensus. What we have to keep in mind is that we could still have scripts
that do not change DB’s schema, but add some table into a table in a minor

Having said that, we are looking for a way to make the upgrade process
smoother,  looking for a way to avoid creating upgrade path manually with
scripts such as <currentVersion>to<newerVersion>, because that way we have
to cover every single upgrade path manually. We can work that out using a
tool to “build and execute” the upgrade path, using a standard to create
and name upgrade routines we have been discussing earlier in this thread.

Erik, there is a tool to do that. As I mentioned in my previous emails
there is a tool called Flywaydb that does exactly what you mentioned.
However, that tool will require an improvement in the way we create and
name upgrade routines; those changes have been cited and discussed earlier.

Paul, about your inquiries:
When you say rollback, do you mean downgrade after an upgrade? If so, we
have discussed that earlier in this thread and we agreed that we would not
cover downgrades, at least for now. The Admin during the upgrade should
properly make a copy of his/her database to be restored if a problem

About the downtime you mentioned, do you mean the need to stop all of the
MS while executing the upgrade?
As a cloud administrator that is built on top of ACS, I find quite the
opposite of you. If I do not look at the source code, I find the upgrade
procedure pretty easy to follow and execute, giving that we just need to
stop all MS and update it with apt-get.
Even if we build a tool as Rohit suggested, the downtime would exist, while
upgrading the database old release of MS would have to be stopped,
otherwise we could receive errors with DB’s schemas change. As I said in
some email earlier, I do not find the need to create a new tool that is
just a wrapper. I prefer to define a standard to create and name upgrade
routines and then use a tool such as Flywaydb directly, which would allow
us to manage solely configurations, instead of wrapper code. IMO the less
code the better.

Paul and Remi, now with Remi’s explanation I understand what you meant with
“downtime”. As Remi’s said the others stack are far worse to upgrade.
OpenStack has a tool such as the suggested “Chimp” that seems to cover
rollbacks. However, I found their upgrade process worse than ours.

We are discussing DB upgrade routines here, I understand the problem of
upgrade as a whole that needs to cover aspect such as SystemVMs upgrade.
However, I think that point should and can be discussed in a separated
thread; as a consequence of that it is a different part of ACS source code.

About reverting an upgrade, I do not find it hard at all; it is basically
restoring the DBs “cloud” and “cloud_usage” to their state prior the
upgrade (giving that in ACS upgrade page, it is stated that you should
backup your databases). Maybe because I am a developer, I do not see much
problem with that.

Bottom line:

There is a tool that can help us with upgrade routines for DB, what we need
is a consensus on how to create and name upgrade routines and the tool that
we can use to build and execute the upgrade path. I think we all agreed
with the standards we had discussed earlier.

Can I create a page in the ACS wiki formalizing the points we discussed
here in regards to ACS DB’s upgrade routines?
I tried to create a child page in, but it
seems that I do not have permission. After that, I can start working in a
PR to change add flywaydb to ACs.

On Wed, Dec 30, 2015 at 2:41 PM, Ron Wheeler <
> wrote:

> On 30/12/2015 4:58 AM, Remi Bergsma wrote:
>> Hoi Paul,
>> Agree that the user perspective is important, thanks for bringing that up.
> It is also worth pointing out that once you get into the SMB space, the
> system admin may wear a few hats and is not dedicated full time to
> maintaining Cloudstack.
> If it works most of the time the way it is supposed to, the admin is not
> spending any time working with the guts of Cloudstack.
> Once it is up and running, the skills and knowledge will decay pretty
> quickly.
> There is a need for an upgrade that works reliably and has good tests that
> can be quickly tried to see that the upgrade has worked or needs to be
> reverted.
>> Remember that the other “Stack” is far worse in upgrades, so it’s all
>> about perspective.
> I guess being the second worst stack is comforting in some way. :-)
>>   Having said that, I also want it to be smooth and we absolutely need it
>> to be outside of the main repo and able to rollback if stuff goes wrong (so
>> users can retry).
>> The biggest other issue I see in upgrading is the systemvm replacement
>> and having to reboot (100s or 1000s of routers). That’s where your real
>> downtime is most of the time.
> If you have done all that and have to revert, it is not very comforting to
> know that most of the time you wasted was spent in a fairly stable process
> and that the downtime can be chalked up to the size of the server
> population. The users will be happy with that, I suppose.
>> Although upgrading from 4.6 to 4.7 takes under 5 minutes (stop ACS,
>> replace RPM and start it again) and no systemvm template needed to be
>> replaced. That’s more like it already ;-)
> That sounds more like what I need!
>> Regards,
>> Remi
>> From: Paul Angus <<mailto:
>> Reply-To: "<>" <
>> Date: Wednesday 30 December 2015 10:10
>> To: "<>" <
>> Subject: RE: Let’s discuss database upgrades
>> Hi Guys, from the user's perspective, there are two points which come up
>> again and again -
>> 1. lack a prescribed roll back if an upgrade goes badly
>> 2. The downtime involved in doing upgrades.
>> - Upgrades are seen as CloudStack's biggest 'issue'.
>> I've had to rescue enough upgrades to understand how complicated it is;
>> however with the increased release velocity, the admin's experience of
>> doing these upgrades needs to be taken into account or we will lose users
>> because of the increased admin overhead and downtime.
>> The purpose of Rohit's CloudChimp was to find a suitable tool/method to
>> carry out schema changes *without downtime*. You guys are far better placed
>> to argue the merits of any one solution than me.
>> I would just ask that you keep in mind what the users are looking for -
>> relatively clean and recoverable upgrade process.
>> [ShapeBlue]<>
>> Paul Angus
>> VP Technology   ,       ShapeBlue
>> d:      +44 203 617 0528 | s: +44 203 603 0540<tel:+44%20203%20617%200528%20|%20s:%20+44%20203%20603%200540>
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>> e: | t: @cloudyangus<mailto:
>>|%20t:%20@cloudyangus>      |      w:
>> a:      53 Chandos Place, Covent Garden London WC2N 4HS UK
>> [cid:image182380.png@8ca21c21.40847519]
>> Shape Blue Ltd is a company incorporated in England & Wales. ShapeBlue
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>> -----Original Message-----
>> From: Erik Weber []
>> Sent: 29 December 2015 21:45
>> To: dev <<>>
>> Subject: Re: Let’s discuss database upgrades
>> On Mon, Dec 28, 2015 at 2:16 PM, Rafael Weingärtner <
>><>> wrote:
>> Hi all devs,
>>> First of all, sorry the long text, but I hope we can start a
>>> discussion here and improve that part of ACS.
>>> A while ago I have faced the code that Apache CloudStack (ACS) uses to
>>> upgrade from a version to newer one and that did not seem to be a good
>>> way to execute our upgrades. Therefore, I decided to use some time to
>>> search for alternatives.
>>> I have read some material about versioning of scripts used to upgrade
>>> a database (DB) of a system and went through some frameworks that
>>> could help us.
>>> In the literature of software engineering, it is firmly stated that we
>>> have to version DB scripts as we do with the source code of the
>>> application, using the baseline approach. Gladly, we were not that bad
>>> at this point, we already versioned our routines for DB upgrade (.sql
>>> and .java). Therefore, it seemed that we just did not have used a
>>> practical approach to help us during DB upgrades.
>>>  From my readings and looking at the ACS source code I raised the
>>> following
>>> requirement:
>>> • We should be able to write more than one routine to upgrade to a
>>> version; those routines can be written in Java and SQL. We might have
>>> more than a routine to be executed for each version and we should be
>>> able to define an order of execution. Additionally, to go to an upper
>>> version, we have to run all of the routines from smaller versions
>>> first, until we achieve the desired version.
>>> We could also add another requirement that is the downgrade from a
>>> version, which we currently do not support. With that comes my first
>>> question for
>>> discussion:
>>> • Do we want/need a method to downgrade from a version to a previous
>>> one?
>>> I found an explanation for not supporting downgrades, and I liked it:
>>> So, what I devised for us:
>>> First the bureaucracy part - our migrations occur basically in three
>>> (3) steps, first we have a "prepare script", then a cleanup script and
>>> finally the migration per se that is written in Java, at least, that
>>> is what we can expect when reading the interface
>>> “”.
>>> Additionally, our scripts have the following naming convention:
>>> schema-<currentVersion>to<desiredVersion>, which in IMHO may cause
>>> some confusion because at first sight we may think that from the same
>>> version we could have different paths to an upper version, which in
>>> practice is not happening. Instead of a <currentVersion>to<version>
>>> could simply use V_<numberOfVersion>_<sequencial>.<fileExtension>,
>>> giving that, we have to execute all of the V_<version> scripts that
>>> are smaller than the version we want to upgrade.
>>> To clarify what I am saying, I will use an example. Let’s say we have
>>> just installed ACS and ran the cloudstack-setup-database. That command
>>> will create a database schema in version 4.0.0. To upgrade that schema
>>> to version 4.3.0 (it is just an example, it could be any other
>>> version), ACS will use the following mapping:
>>> _upgradeMap.put("4.0.0", new DbUpgrade[] {new Upgrade40to41(), new
>>> Upgrade410to420(), new Upgrade420to421(), new Upgrade421to430())
>>> After loading the mapping, ACS will execute the scripts defined in
>>> each one of the Upgrade path classes and the migration code per se.
>>> Now, let’s say we change the “.sql” scripts name to the pattern I
>>> mentioned, we would have the following scripts; those are the scripts
>>> found that aim to upgrade to versions between the interval 4.0.0 –
>>> 4.3.0 (considering 4.3.0, since that is the goal version):
>>> - schema-40to410, can be named to: V_410_A.sql
>>> - schema-40to410-cleanup, can be named to: V_410_B.sql
>>> - schema-410to420, can be named to: V_420_A.sql
>>> - schema-410to420-cleanup , can be named to: V_420_b.sql
>>> - schema-420to421, can be named to: V_421_A.sql
>>> - schema-421to430, can be named to: V_430_A.sql
>>> - schema-421to430-cleanup, can be named to: V_430_B.sql
>>> Additionally, all of the java code would have to follow the same
>>> convention. For instance, we have
>>> “”,
>>> which has some java code to migrate from 4.0.0 to 4.1.0. The idea is
>>> to extract that migration code to a Java class named:,
>>> giving that it has to execute the SQL scripts before the java code.
>>> In order to go from a smaller version (4.0.0) to an upper one (4.3.0),
>>> we have to run all of the migration routines from intermediate
>>> versions. That is what we are already doing, but we do all of that
>>> manually.
>>> Bottom line, I think we could simple use the convention
>>> V_<numberOfVersion>_<sequencial>.<fileExtension> to name upgrade
>>> routines.
>>> That would facilitate us to use a framework to help us with that process.
>>> Additionally, I believe that we should always assume that to go from a
>>> smaller version to a higher one, we should run all of the scripts that
>>> exist between them. What do you guys think of that?
>>> After the bureaucracy, we can discuss tools. If we use that convention
>>> to name migration (upgrade) routines, we can start thinking on tools
>>> to support our migration process. I found two (2) promising ones:
>>> Liquibase and Flywaydb (both seem to be under Apache license, but the
>>> first one has an enterprise version?!). After reading the
>>> documentation and some usage examples I found the flywaydb easier and
>>> simpler to use.
>>> What are the options of tools that we can use to help us manage the
>>> database upgrade, without needing to code the upgrade path that you know?
>>> After that, I think we should decide if we should create another
>>> project/component to take care of migrations, or we can just add the
>>> dependency of the tool to a project such as “cloud-framework-db” and
>>> start using it.
>>> The “cloud-framework-db” project seems to have a focus on other things
>>> such as managing transactions and generating SQLs from annotations
>>> (?!? That should be a topic for another discussion). Therefore, I
>>> would rather create a new project that has the specific goal of
>>> managing ACS DB upgrades. I would also move all of the routines (SQL and
>>> Java) to this new project.
>>> This project would be a module of the CloudStack project and it would
>>> execute the upgrade routines at the startup of ACS.
>>> I believe that going from a homemade solution to one that is more
>>> consolidated and used by other communities would be the way to go.
>>> I can volunteer myself to create a PR with the aforementioned changes
>>> and using flywaydb to manage our upgrades. However, I prefer to have a
>>> good discussion with other devs first, before starting coding.
>>> Do you have suggestions or points that should be raised before we
>>> start working on that?
>> This isn't my field of work, so forgive me if this is self explanatory or
>> something, but is there no tool like terraform/puppet or similar for
>> database work?
>> I mean, where you state you desired state and the tool handles it.
>> To me it sounds like a good way would be if you could specify what you
>> want to exist (or not), and how it should look like.
>> "I want table XYZ to exist with THESE columns having THIS type(s) and
>> THIS default value bla bla bla"
>> Rather than handling a bunch of sql scripts that has to handle different
>> mysql versions (come to think about an issue with a mariadb version
>> crashing recently), a variety of cloudstack versions and a whole lot more.
>> Disclaimer: i have no idea if this is what flywaydb does, if it is, then
>> just ignore this.
>> --
>> Erik
>> Find out more about ShapeBlue and our range of CloudStack related
>> services:
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>>> | CSForge – rapid
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> --
> Ron Wheeler
> President
> Artifact Software Inc
> email:
> skype: ronaldmwheeler
> phone: 866-970-2435, ext 102

Rafael Weingärtner

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