Thanks for your responses. > I don't see a need of protobuf for this particular usecase
If no one else feels strongly on this point, I am good with using a POJO. > It doesn't matter if it's system-topic or not because it's > configurable and the admin of the system can decide and configure it > according to the required persistent policy. On my first reading, it wasn't clear if there was only one topic required for this feature. I now see that the topic is not tied to a specific tenant or namespace. As such, we can avoid complicated authorization questions by putting the required event topic(s) into a "system" tenant and namespace, by default. The `pulsar/system` tenant and namespace seem appropriate to me. > I would keep the system topic > separate because this topic serves a specific purpose with specific schema, > replication policy and retention policy. I think we need a more formal definition for system topics. This topic is exactly the kind of topic I would call a system topic: its intended producers and consumers are Pulsar components. However, because this feature can live on a topic in a system namespace, we can avoid the classification discussion for this PIP. > Source region will have a broker which will create a failover consumer on > that topic and a broker with an active consumer will watch the metadata > changes and publish the changes to the event topic. How do we designate the host broker? Is it manual? How does it work when the host broker is removed from the cluster? If we collocate the active consumer with the broker hosting the event topic, can we skip creating the failover consumer? > PIP briefly talks about it but I will update the PIP with more > explanation. I look forward to seeing more about this design for conflict resolution. Thanks, Michael On Tue, Feb 1, 2022 at 3:01 AM Rajan Dhabalia <dhabalia...@gmail.com> wrote: > > Please find my response inline. > > On Mon, Jan 31, 2022 at 9:17 PM Michael Marshall <mmarsh...@apache.org> > wrote: > > > I think this is a very appropriate direction to take Pulsar's > > geo-replication. Your proposal is essentially to make the > > inter-cluster configuration event driven. This increases fault > > tolerance and better decouples clusters. > > > > Thank you for your detailed proposal. After reading through it, I have > > some questions :) > > > > 1. What do you think about using protobuf to define the event > > protocol? I know we already have a topic policy event stream > > defined with Java POJOs, but since this feature is specifically > > designed for egressing cloud providers, ensuring compact data transfer > > would keep egress costs down. Additionally, protobuf can help make it > > clear that the schema is strict, should evolve thoughtfully, and > > should be designed to work between clusters of different versions. > > > > >>> I don't see a need of protobuf for this particular usecase because of > two reasons: > >> a. policy changes don't generate huge traffic which could be 1 rps b. > and it doesn't need performance optimization. > >> It should be similar as storing policy in text instead protobuf which > doesn't impact footprint size or performance due to limited number of > >> update operations and relatively less complexity. I agree that protobuf > could be another option but in this case it's not needed. Also, POJO > >> can also support schema and versioning. > > > > > > > 2. In your view, which tenant/namespace will host > > `metadataSyncEventTopic`? Will there be several of these topics or is > > it just hosted in a system tenant/namespace? This question gets back > > to my questions about system topics on this mailing list last week [0]. I > > view this topic as a system topic, so we'd need to make sure that it > > has the right authorization rules and that it won't be affected by calls > > like "clearNamespaceBacklog". > > > >> It doesn't matter if it's system-topic or not because it's > configurable and the admin of the system can decide and configure it > according to the required persistent policy. I would keep the system topic > separate because this topic serves a specific purpose with specific schema, > replication policy and retention policy. > > > > > > > 3. Which broker will host the metadata update publisher? I assume we > > want the producer to be collocated with the bundle that hosts the > > event topic. How will this be coordinated? > > > >> It's already explained into PIP in section: "Event publisher and handler" > >> Every isolated cluster deployed on a separate cloud platform will have a > source region and part of replicated clusters for the event topic. The > Source region will have a broker which will create a failover consumer on > that topic and a broker with an active consumer will watch the metadata > changes and publish the changes to the event topic. > > > > > > > 4. Why isn't a topic a `ResourceType`? Is this because the topic level > > policies already have this feature? If so, is there a way to integrate > > this feature with the existing topic policy feature? > > > >> Yes, ResourceType can be extensible to a topic as well. > > > > > > > 5. By decentralizing the metadata store, it looks like there is a > > chance for conflicts due to concurrent updates. How do we handle those > > conflicts? > > > >> PIP briefly talks about it but I will update the PIP with more > explanation. MetadataChangeEvent contains source-cluster and updated time. > Also, resources Tenant/Namespace will also contain lastUpdatedTime which > will help to destination clusters to handle stale/duplicate events and race > conditions. Also, snapshot-sync an additional task helps all clusters to be > synced with each other eventually. > > > > > I'll also note that I previously proposed a system event topic here > > [1] and it was proposed again here [2]. Those features were for > > different use cases, but ultimately looked very similar. In my view, a > > stream of system events is a very natural feature to expect in a > > streaming technology. I wonder if there is a way to generalize this > > feature to fulfill local cluster consumers and geo-replication > > consumers. Even if this PIP only implements the geo-replication > > portion of the feature, it'd be good to design it in an extensible fashion. > > > >> I think answer (2) addresses this concern as well. > > > > > Thanks, > > Michael > > > > [0] https://lists.apache.org/thread/pj4n4wzm3do8nkc52l7g7obh0sktzm17 > > [1] https://lists.apache.org/thread/h4cbvwjdomktsq2jo66x5qpvhdrqk871 > > [2] https://lists.apache.org/thread/0xkg0gpsobp0dbgb6tp9xq097lpm65bx > > > > > > > > On Sun, Jan 30, 2022 at 10:33 PM Rajan Dhabalia <rdhaba...@apache.org> > > wrote: > > > > > > Hi, > > > > > > I would like to start a discussion about PIP-136: Sync Pulsar policies > > > across multiple clouds. > > > > > > PIP documentation: https://github.com/apache/pulsar/issues/13728 > > > > > > *Motivation* > > > Apache Pulsar is a cloud-native, distributed messaging framework which > > > natively provides geo-replication. Many organizations deploy pulsar > > > instances on-prem and on multiple different cloud providers and at the > > same > > > time they would like to enable replication between multiple clusters > > > deployed in different cloud providers. Pulsar already provides various > > > proxy options (Pulsar proxy/ enterprise proxy solutions on SNI) to > > fulfill > > > security requirements when brokers are deployed on different security > > zones > > > connected with each other. However, sometimes it's not possible to share > > > metadata-store (global zookeeper) between pulsar clusters deployed on > > > separate cloud provider platforms, and synchronizing configuration > > metadata > > > (policies) can be a critical path to share tenant/namespace/topic > > policies > > > between clusters and administrate pulsar policies uniformly across all > > > clusters. Therefore, we need a mechanism to sync configuration metadata > > > between clusters deployed on the different cloud platforms. > > > > > > *Sync Pulsar policies across multiple clouds* > > > https://github.com/apache/pulsar/issues/13728 > > > Prototype git-hub-link > > > < > > https://github.com/rdhabalia/pulsar/commit/e59803b942918076ce6376b50b35ca827a49bcf6 > > > > > > Thanks, > > > Rajan > >
