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From Wido den Hollander <>
Subject Re: Let’s discuss database upgrades
Date Tue, 29 Dec 2015 10:15:55 GMT

On 28-12-15 21:34, Rafael Weingärtner wrote:
> Hi Wido, Rohit,
> I have just read the feature suggestion.
> Wido, I am not trying to complicate things, quite the opposite, I just
> illustrate a simple thing that can happen and is happening; I just pointed
> how it can be easily solved.
> About the release of .Z, releases more constant and others, I do not want
> to mix topics. Let’s keep this thread strict to discuss database upgrades.

I do not want to start the release discussion, but what I meant is that
we try to find a technical solution to something which might be solved
easier by just changing the way we release.

4.6.0 is released and afterwards 4.5.3 is released. How does somebody
upgrade from 4.5.3 to 4.6.0? He can't, since the 4.6.0 code doesn't
support that path.

So my idea is to split the database version from the code version.

The code requires database version >= X and during boot it simply checks

The database migration tool can indeed do the DB migration, it doesn't
have to be the mgmt server who does the upgrade.

> Now, about the FS. I agree with Rohit that we should have only one way of
> managing database upgrades and creation. I just do not like the idea of
> creating a tool that work as a wrapper on frameworks/tools such as
> flywaydb. I think that those frameworks already work pretty good as they
> are; and, I would rather maintain configurations than some wrapper code.
> I personally like the way ACS works during upgrades (I just do not like the
> code itself and how things are structured), as a system administrator I
> like to change the version in the “/etc/apt/sources.list.d/cloudstack.list”
> and use the "apt-get" "update" and "install" from the command line. I do
> not see the need to add another tool that is just a wrapper to the mix. If
> I update ACS code to 4.7.0, why would I let the database schema in an older
> version? And if we want version DB schemas and application code separately
> maintaining somehow compatibility between them, which would bring a whole
> other level of complexity to the code; I think we should avoid that.
> The flywaydb can be easily integrated with everything we have now; we could
> have a maven profile for developers and integrate it in ACS bootstrap using
> its API as a Spring bean. Therefore, we could remove the current
> “DatabaseUpgradeChecker “, “DbUpgrade” and other classes that aim to do
> that. We could even add the creation of the schema into the first time it
> boots using flywaydb and retire the “cloudstack-setup-database” script, or
> at least make it less complicated, using it just to configure the database
> URL and users.
> The point is that to use Flywaydb we would have to agree upon a convention
> on creating routines (java and SQL) to execute upgrades. Moreover, using a
> tool such as Flywaydb we do not need to worry about upgrade paths. As I
> wrote in the email I used to start this thread, the upgrade has to be
> straightforward, to go to a version we have to run all of the upgrade
> routines between the current version until the desired one. Our job is to
> create upgrade routines that work and name them properly, the job of the
> tool is to check the current version, the desired one, the upgrades that it
> needs to run and execute everything properly.

Yes, indeed. I just wanted to start the discussion if we shouldn't
version the database differently from the code.

> Additionally, I do not see the need to break compatibility as Rohit
> suggested in the FS; in my opinion, everything we have up today can be
> migrated to the new structure I proposed. If we use a tool such as
> Flywaydb, I even volunteered for that. The only thing we have to discuss
> and agree upon is the naming conventions for upgrades routines, where to
> put them and the configurations for flywaydb.
> Thanks for your contribution and time.
> On Mon, Dec 28, 2015 at 2:10 PM, Rohit Yadav <>
> wrote:
>> Hi Rafael and Wido,
>> Thanks for starting a conversation in this regard, I could not pursue the
>> Chimp tool due to other $dayjob work though it’s good to see some
>> discussion has started again. Hope we’ll solve this in 2016.
>> In my opinion, we will need to first separate the database init/migration
>> tooling away from mgmt server (right now the mgmt server does db migrations
>> when it starts and there is a code/db version mismatch) and secondly make
>> sure that we’re using the same code/tool to deploy database (right now,
>> users use the cloudstack-setup-database python tool while developer use the
>> maven/java DatabaseCreator activated by the -Ddeploydb flag).
>> After we’ve addressed these two issues we can look into how we can support
>> minor releases workflow (or decide to do something else, like not support
>> .Z releases like Wido mentioned), and see if we can or want to use any
>> existing migration tool or write a wrapper tool “chimp” that uses existing
>> tools (some of those are mentioned in the Chimp FS like flywaydb etc). For
>> allowing users to go back and forth from a db schema/version, we’ll also
>> need some new DB migration conventions/versioning/rules/static-checking,
>> and how developer need to write such paths (forward and reverse) etc.
>> The best approach I figured at the time was to decide that we’ll use the
>> previous db upgrade path mechanism till a certain CloudStack version (say
>> 4.8.0) and after that we’ll use the new approach or tooling to
>> upgrade/downgrade DB schemas (thereby retiring away from the old DB upgrade
>> path mess).
>> [image: ShapeBlue] <> Rohit Yadav Software
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>> On 28-Dec-2015, at 9:10 PM, Wido den Hollander <> wrote:
>>> On 28-12-15 16:21, Rafael Weingärtner wrote:
>>>> Thanks for your contribution Wido,
>>>> I have not seen Rohit’s email; I will take a look at it.
>>> Ok, he has a FS here:
>>>> About database schema changes happening only in X.Y, I also agree with
>> you
>>>> (that is a convention we all could agree on, and such as conding and
>>>> release procedures we could have a wiki page for that). However, I
>> think we
>>>> still might have scripts in versions X.Y.Z to add data to a table such
>> as
>>>> “guest_os_hypervisor”.
>>> Yes, that is true. A bugfix could be a addition into the database, but
>>> we have to prevent it as much as possible.
>>>> The point to manage such scripts is that, if we are in version such as
>>>> 4.7.0 and a new script emerges in version 4.5.3, we would have to
>> decide to
>>>> run or not to run it. I would rather not run them, since if they add
>>>> something to the code base; those changes should also be applied into
>>>> master and as a consequence it will be available in a future update.
>>> I understand, but this is where our release cycle becomes the problem.
>>> It is because we release a X.Y.Z release we run into these kind of
>> problems.
>>> If we as a project simple do not release the .Z releases we would be
>>> fine as well ;)
>>> You can try to complicate things with technical things, or if we release
>>> every two / three weeks we don't run into these kind of situations :)
>>> We might even cut the database version loose from the code version.
>>> Database version is simple 100, 101, 102, 103, 104, 105. And a code
>>> version requires a certain version of the database.
>>> Wido
>>>> On Mon, Dec 28, 2015 at 12:50 PM, Wido den Hollander <>
>> wrote:
>>>>> On 28-12-15 14:16, 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
>>>>>> upgrade from a version to newer one and that did not seem to be a
>>>>> way
>>>>>> to execute our upgrades. Therefore, I decided to use some time to
>> search
>>>>>> for alternatives.
>>>>> I think we all saw that happen once or more :)
>>>>>> 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
>>>>> 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
>> 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
>>>>>> version; those routines can be written in Java and SQL. We might
>>>>> 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
>>>>>> achieve the desired version.
>>>>>> We could also add another requirement that is the downgrade from
>>>>> 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 personally do not care. Usually people should create a backup PRIOR
>> to
>>>>> a upgrade. If that fails they can restore the backup.
>>>>>> I found an explanation for not supporting downgrades, and I liked
>>>>>> 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
>> not
>>>>>> happening. Instead of a <currentVersion>to<version> we
could simply
>> use
>>>>>> V_<numberOfVersion>_<sequencial>.<fileExtension>,
giving that, we
>> have to
>>>>>> execute all of the V_<version> scripts that are smaller than
>> version
>>>>> we
>>>>>> want to upgrade.
>>>>>> To clarify what I am saying, I will use an example. Let’s say we
>>>>> just
>>>>>> installed ACS and ran the cloudstack-setup-database. That command
>>>>>> create a database schema in version 4.0.0. To upgrade that schema
>>>>>> 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
>>>>>> 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
>> 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
>>>>>> smaller version to a higher one, we should run all of the scripts
>>>>>> exist between them. What do you guys think of that?
>>>>> That seems good to me. But we still have to prevent that we perform
>>>>> database changes in a X.Y.Z release since that is branched off to a
>>>>> different branch.
>>>>> Imho database changes should only happen in X.Y releases.
>>>>>> After the bureaucracy, we can discuss tools. If we use that
>> convention to
>>>>>> name migration (upgrade) routines, we can start thinking on tools
>>>>>> support our migration process. I found two (2) promising ones:
>> Liquibase
>>>>>> and Flywaydb (both seem to be under Apache license, but the first
>> 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
>>>>>> dependency of the tool to a project such as “cloud-framework-db”
>>>>> start
>>>>>> using it.
>>>>>> The “cloud-framework-db” project seems to have a focus on other
>>>>> 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
>> 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?
>>>>> Rohit suggested Chimp earlier this year:
>>>>> The thread is called: "[DISCUSS] Let's fix CloudStack Upgrades and DB
>>>>> migrations with CloudStack Chimp"
>>>>> Maybe there is something good in there.
>>>>>> --
>>>>>> Rafael Weingärtner
>> Regards.
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