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Re: Side Car New Repo vs not


I think the following is a very big plus of it being in tree:
>> * Faster iteration speed in general. For example when we need to add a
>> new
>> JMX endpoint that the sidecar needs, or change something from JMX to a
>> virtual table (e.g. for repair, or monitoring) we can do all changes
>> including tests as one commit within the main repository and don't have
>> to
>> commit to main repo, sidecar repo, 

I also don’t see a reason why the sidecar being in tree means it would not work in a mixed version cluster.  The nodes themselves must work in a mixed version cluster during a rolling upgrade, I would expect any management side car to operate in the same manor, in tree or not.

This tool will be pretty tightly coupled with the server, and as someone with experience developing such tightly coupled tools, it is *much* easier to make sure you don’t accidentally break them if they are in tree.  How many times has someone updated some JMX interface, updated nodetool, and then moved on?  Breaking all the external tools not in tree, without realizing it.  The above point about being able to modify interfaces and the side car in the same commit is huge in terms of making sure someone doesn’t inadvertently break the side car while fixing something else.

-Jeremiah


> On Aug 21, 2018, at 10:28 AM, Jonathan Haddad <jon@xxxxxxxxxxxxx> wrote:
> 
> Strongly agree with Blake.  In my mind supporting multiple versions is
> mandatory.  As I've stated before, we already do it with Reaper, I'd
> consider it a major misstep if we couldn't support multiple with the
> project - provided admin tool.  It's the same reason dtests are separate -
> they work with multiple versions.
> 
> The number of repos does not affect distribution - if we want to ship
> Cassandra with the admin / repair tool (we should, imo), that can be part
> of the build process.
> 
> 
> 
> 
> On Mon, Aug 20, 2018 at 9:21 PM Blake Eggleston <beggleston@xxxxxxxxx>
> wrote:
> 
>> If the sidecar is going to be on a different release cadence, or support
>> interacting with mixed mode clusters, then it should definitely be in a
>> separate repo. I don’t even know how branching and merging would work in a
>> repo that supports 2 separate release targets and/or mixed mode
>> compatibility, but I’m pretty sure it would be a mess.
>> 
>> As a cluster management tool, mixed mode is probably going to be a goal at
>> some point. As a new project, it will benefit from not being tied to the C*
>> release cycle (which would probably delay any sidecar release until
>> whenever 4.1 is cut).
>> 
>> 
>> On August 20, 2018 at 3:22:54 PM, Joseph Lynch (joe.e.lynch@xxxxxxxxx)
>> wrote:
>> 
>> I think that the pros of incubating the sidecar in tree as a tool first
>> outweigh the alternatives at this point of time. Rough tradeoffs that I
>> see:
>> 
>> Unique pros of in tree sidecar:
>> * Faster iteration speed in general. For example when we need to add a
>> new
>> JMX endpoint that the sidecar needs, or change something from JMX to a
>> virtual table (e.g. for repair, or monitoring) we can do all changes
>> including tests as one commit within the main repository and don't have
>> to
>> commit to main repo, sidecar repo, and dtest repo (juggling version
>> compatibility along the way).
>> * We can in the future more easily move serious background functionality
>> like compaction or repair itself (not repair scheduling, actual
>> repairing)
>> into the sidecar with a single atomic commit, we don't have to do two
>> phase
>> commits where we add some IPC mechanism to allow us to support it in
>> both,
>> then turn it on in the sidecar, then turn it off in the server, etc...
>> * I think that the verification is much easier (sounds like Jonathan
>> disagreed on the other thread, I could certainly be wrong), and we don't
>> have to worry about testing matrices to assure that the sidecar works
>> with
>> various versions as the version of the sidecar that is released with that
>> version of Cassandra is the only one we have to certify works. If people
>> want to pull in new versions or maintain backports they can do that at
>> their discretion/testing.
>> * We can iterate and prove value before committing to a choice. Since it
>> will be a separate artifact from the start we can always move the
>> artifact
>> to a separate repo later (but moving the other way is harder).
>> * Users will get the sidecar "for free" when they install the daemon,
>> they
>> don't need to take affirmative action to e.g. be able to restart their
>> cluster, run repair, or back their data up; it just comes out of the box
>> for free.
>> 
>> Unique pros of a separate repository sidecar:
>> * We can use a more modern build system like gradle instead of ant
>> * Merging changes is less "scary" I guess (I feel like if you're not
>> touching the daemon this is already true but I could see this being less
>> worrisome for some).
>> * Releasing a separate artifact is somewhat easier from a separate repo
>> (especially if we have gradle which makes e.g. building debs and rpms
>> trivial).
>> * We could backport to previous versions without getting into arguments
>> about bug fixes vs features.
>> * Committers could be different from the main repo, which ... may be a
>> useful thing
>> 
>> Non unique pros of a sidecar (could be achieved in the main repo or in a
>> separate repo):
>> * A separate build artifact .jar/.deb/.rpm that can be installed
>> separately. It's slightly easier with a separate repo but certainly not
>> out
>> of reach within a single repo (indeed the current patch already creates a
>> separate jar, and we could create a separate .deb reasonably easily).
>> Personally I think having a separate .deb/.rpm is premature at this point
>> (for companies that really want it they can build their own packages
>> using
>> the .jars), but I think it really is a distracting issue from where the
>> patch should go as we can always choose to remove experimental .jar files
>> that the main daemon doesn't touch.
>> * A separate process lifecycle. No matter where the sidecar goes, we get
>> the benefit of restarting it being less dangerous for availability than
>> restarting the main daemon.
>> 
>> That all being said, these are strong opinions weakly held and I would
>> rather get something actually committed so that we can prove value one
>> way
>> or the other and am therefore, of course, happy to put sidecar patches
>> wherever someone can review and commit it.
>> 
>> -Joey
>> 
>> On Mon, Aug 20, 2018 at 1:52 PM sankalp kohli <kohlisankalp@xxxxxxxxx>
>> wrote:
>> 
>>> Hi,
>>> I am starting a new thread to get consensus on where the side car
>>> should be contributed.
>>> 
>>> Please send your responses with pro/cons of each approach or any other
>>> approach. Please be clear which approach you will pick while still
>> giving
>>> pros/cons of both approaches.
>>> 
>>> Thanks.
>>> Sankalp
>>> 
>> 
> 
> 
> -- 
> Jon Haddad
> http://www.rustyrazorblade.com
> twitter: rustyrazorblade


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