In the current implementation, ACM supports multi-participant with same supported element Type but different participantId, so they need different properties file.
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Participant replicas can be a kubernetes StatefulSets that consume different properties file with unique consumer groups and unique UUIDs/replica (participants with same UUIDs have different replica number).
The StatefulSet uses the SPRING_CONFIG_NAME environment variable pointing to the spring application properties file unique to each of the participant replica.
Each of the properties file with the names pod-0.yaml, pod-1.yaml is mounted to the volumes. And the SPRING_CONFIG_NAME variable can be set to /path/to/$HOSTNAME.yaml to use the corresponding
properties file.
By this approach the participant can have multiple replicas to work with a shared data.
env:
- name: HOSTNAME
valueFrom:
fieldRef:
fieldPath: metadata.name
- name: SPRING_CONFIG_NAME
value: /path/to/${HOSTNAME}.yaml
For example considering the http participant replica, ${HOSTNAME} will be "policy-http-ppnt-0" and "policy-http-ppnt-1" and their
corresponding properties files with the names "http-ppnt-0.yaml" and "http-ppnt-1.yaml" is volume mounted.
Note: In a scenario of two participants in replicas (we are calling "policy-http-ppnt-0" and "policy-http-ppnt-1"), ACM-Runtime will assignee as before any composition definition in prime time to specific participant based of supported element definition type. All participants will receive the same messages and store same data, so all participants are synchronized with ACM-R. Into all messages from ACM-R to participants will be present the replica number to indicate what participant will do the job (like prime or deploy). Example ACM-R send deploy message with replica 0, so "policy-http-ppnt-0" save the new instance and deploy and "policy-http-ppnt-1" just save that instance. When "policy-http-ppnt-0" send outProperties, then ACM-R and "policy-http-ppnt-1" receive the message and save that properties. When "policy-http-ppnt-0" has completed the deploy, the send the message and then then ACM-R and "policy-http-ppnt-1" receive the message and save the result. No issue if ACM-R send an undeploy message with replica 1, because all applications are synchronized.
Changes in Participant:
- Register, Status and Unregister message have to contain the replica number
- store data from messages from ACM-R if the participantId is matching and enable the actions only if the participantId and replica number are matching with the message
- store data (outProperties, and action completed) from messages from participants with same participantId and different replica
- implement time-out to stop the process if is running out of time
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- Participant Design backward compatibility is preserved, there is no change to the participant intermediary interface for participant implementations
- Participant Configuration Backward compatibility is preserved, apart from a new "replicas" parameter (optional, default is 1), there is no change to participant configuration
- ACM-R introduces a new REST API for replica management
- ACM-R is made HA so that it itself can scale
- We can use Kafka load balancing on the participants and get the load balancing functionality for nothing
Optimal Solution:
After analysis, it is clear that the best solution to use is number 3.
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