imjyz opened a new issue, #9754:
URL: https://github.com/apache/rocketmq/issues/9754
### Is Your Feature Request Related to a Problem?
No
### Describe the Solution You'd Like
**The consumer client supports defining a consumer-tag and
consumer-tag-filter-conditions.**
* **consumer-tag**: The label defined by the consumer client for itself, not
to the message. Different consumers within the same consumer-group can be
configured with different tags.
* **consumer-tag-filter-conditions**: Filtering criteria defined by the
consumer client based on message attributes, determining which messages can
match the current consumer-tag; this is different from the filtering
expressions used in subscription.
**Constraints**
* Each consumer is allowed to have only one tag (consumer-tag).
* There must be a one-to-one correspondence between consumer-tag and
filter-conditions; within the same consumer group, it is strictly prohibited to
have one consumer-tag associated with multiple filter-conditions.
* Consumers without a configured tag will be treated as having the default
tag.
* Only pop consumers are supported.
**Changes on the broker side**
When a consumer pulls messages, it can only retrieve messages that match
its consumer-tag.
**Fallback**
Perhaps we can incorporate the fallback configuration into the subscription.
When fallback is allowed, messages that fail to match a specific consumer-tag
will be consumed by the consumer with the default tag; when fallback is not
allowed, unmatched messages can be routed to a dead-letter queue.
**Note📢**
The subscription remains unchanged; the consumer-tag is only used to
determine which specific consumer within the consumer group will consume the
messages delivered to the group.
**Scenario without consumer-tag**
<img width="804" height="278" alt="Image"
src="https://github.com/user-attachments/assets/3121d4f2-17ea-4990-9100-b369b469317f";
/>
**Scenario with consumer-tag**
<img width="781" height="353" alt="Image"
src="https://github.com/user-attachments/assets/ff17d7dd-7cb1-46bf-b0a4-2da50a3b7811";
/>
### Describe Alternatives You've Considered
Reference: https://github.com/apache/rocketmq/issues/8468
This approach requires producers to cooperate in tagging, involves heavier
publishing overhead, and cannot flexibly support multiple environments.
### Additional Context
In RocketMQ, all consumers under a consumer group evenly consume messages
from the subscription. However, in certain scenarios, it is desired for
different consumers to consume different messages (e.g., multi-environment
deployments, canary releases, etc.).
Although this can be achieved by creating separate consumer groups, it
introduces additional operational overhead and lacks flexibility, making it
unable to support fallback scenarios.
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