PIP-10: Remove cluster for namespace and topic names

• Status: Implemented
• Author: Matteo Merli
• Pull Request: #1150
• Mailing List discussion:
• Release: 2.0.0

Motivation

Currently in Pulsar there is a distinction between local and global topics, where global topics are replicated and local topics are not.

A topic is global if it's created on a global namespace and local if it's created on a namespace that it's tied to a particular Pulsar cluster.

For example:

• Global namespace --> my-tenant/global/my-namespace
• Local namespace --> my-tenant/us-west/my-namespace

Similarly, the topic names will follow as:

• Global topic --> persistent://my-tenant/global/my-namespace/my-topic
• Local topic --> persistent://my-tenant/us-west/my-namespace/my-topic

This distinction leads to a few confusing side effects:

• Global it's kind of an overloaded term and everyone has a different view of it
• If a user starts with local topic in a single cluster, later this cannot be converted into a global topic directly, because the topic name already include the particular cluster
• Looking at the topic or namespace name, there is the wrong impression of a hierarchy between a tenant and a cluster, while in reality there is a many to many relationship between the two.

In reality, the difference between the two types is only coming from legacy reason and there is no practical difference between a global with just one single cluster in the replication list and a local namespace.

Given that local namespace is just a special case in the more general global namespace, this proposal is to make all the namespaces to be global.

Once all the namespaces are global, there will be no need to specify global in the namespace or topic names. Thus the names could be simplified like in:

• Namespace --> my-tenant/my-namespace
• Topic --> persistent://my-tenant/my-namespace/my-topic

Existing namespaces and topics will continue work as before. All REST APIs and tools will accept both naming schemes, though the documentation will just refer to the new naming, to avoid confusion.

Changes

• NamespaceName and DestinationName are the only classes that are used to do the naming validation and will be updated to support both old and new scheme.
• When creating a namespace we will add an option to immediately specify the replication clusters, to avoid multiple CLI commands or REST calls.
• Admin API REST URL handlers will need to be adapted because they're based on expecting a certain number of / in the URL. New handlers will be added and the old ones will be marked as "hidden" for the auto-generated documentation in Swagger.
• Examples and test will be converted to use the new convention. Most tests will not be converted at this point, to ensure both old and new scheme can coexist.