Hey Paul, thanks for the kind words re MM2.
I'm not a Streams expert first off, but I think I understand your question:
if a Streams app can switch between topics with and without a cluster alias
prefix when you migrate between prod and pre-prod, while preserving state.
Streams supports regexes and lists of topics as input, so you can use e.g.
builder.stream(List.of("topic1", "prod.topic1")), which is a good place to
start. In this case, the combined subscription is still a single stream,
conceptually, but comprises partitions from both topics, i.e. partitions
from topic1 plus partitions from prod.topic1. At a high level, this is no
different than adding more partitions to a single topic. I think any
intermediate or downstream topics/tables would remain unchanged, since they
are still the result of this single stream.
The trick is to correctly translate offsets for the input topics when
migrating the app between prod and pre-prod, which RemoteClusterUtils can
help with. You could do this with external tooling, e.g. a script
leveraging RemoteClusterUtils and kafka-streams-application-reset.sh. I
haven't tried this with a Streams app myself, but I suspect it would work.
Ryanne
On Sun, Mar 24, 2019 at 12:31 PM Paul Whalen <pgwha...@gmail.com> wrote:
> Hi all,
>
> With MirrorMaker 2.0 (
>
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-382%3A+MirrorMaker+2.0
> )
> accepted and coming along very nicely in development, it has got me
> wondering if a certain use case is supported, and if not, can changes be
> made to Streams or MM2 to support it. I'll explain the use case, but the
> TL;DR here is "do we need more control over topic naming in MM2 or
> Streams?"
>
> My team foresees using MM2 as a way to mirror data from our prod
> environment to a pre-prod environment. The data is supplied by external
> vendors, introduced into our system through a Kafka Streams ETL pipeline,
> and consumed by our end-applications. Generally we would only like to run
> the ETL pipeline in prod since there is an operational cost to running it
> in both prod and pre-prod (the data sometimes needs manual attention).
> This seems to fit MM2 well: pre-prod end-applications consume from the
> pre-prod Kafka cluster, which is entirely "remote" topics being mirrored
> from the prod cluster. We only have to keep one instance of the ETL
> pipeline running, but end-applications can be separate, connecting to their
> respective prod and pre-prod Kafka clusters.
>
> However, when we want to test changes to the ETL pipeline itself, we would
> like to turn off the mirroring from prod to pre-prod, and run the ETL
> pipeline also in pre-prod, picking up the most recent state of the prod
> pipeline from when mirroring was turned off (FWIW, downtime is not an issue
> for our use case).
>
> My question/concern is basically, can Streams apps work when they're
> running against topics prepended with a cluster alias, like
> "pre-prod.App-statestore-changelog" as is the plan with MM2. From what I
> can tell the answer is no, and my proposal would be to give the Streams
> user more specific control over how Streams names its internal topics
> (repartition and changelogs) by defining an "InternalTopicNamingStrategy"
> or similar. Perhaps there is a solution on the MM2 side as well, but it
> seems much less desirable to budge on that convention.
>
> I phrased the question in terms of my team's problem, but it's worth noting
> that this use case is passably similar to a potential DR use case, where
> there is a DR cluster that is normally just being mirrored to by MM2, but
> in a DR scenario would become the active cluster that Streams applications
> are connected to.
>
> Thanks for considering this issue, and great job to those working on MM2 so
> far!
>
> Paul
>
