References:

CPS-1005 - Getting issue details... STATUS

Overview:

This POC is for finding ways to create a resource (NCMP for this instance).

Few possibilities were discussed during the Grooming session which are listed as below.

1. init-container
2. k8s hooks
3. Events in Spring.
4. Sidecar container

Issues and decisions

Analysis

1. init-container
   
   Init containers are exactly like regular containers, except:
       -  Init containers always run to completion.
       -  Each init container must complete successfully before the next one starts.
   
   Since our application container would not be running the before the init-container so we cant invoke any endpoint to create a resource and we dont want to go with DB related script(SQL) to create a resource (insert a row in the database) so I am not exploring this further for this use case.
   
   
2. k8s hooks
   
   - postStart hook : It runs only once and if it fails the container is unable to start. No provision to restart / retry.
   
   

3. Events in Spring
   
   We can use the ApplicationReadyEvent which is published when the application is ready to service requests.
   We can listen to this event , which is thrown by the SpringApplication itself and then execute some code (which is creating a dataspace in our scenario)
   
   Example
   
   

   ApplicationReadyEvent

   @EventListener(ApplicationReadyEvent.class)
       public void initializeNcmp() {
           log.info("Initializing NCMP when the ApplicationReadyEvent is received");
           try {
               cpsAdminService.createDataspace("NCMP-CmHandle-Operational-Data");
           } catch (final AlreadyDefinedException ex) {
               log.info("Already defined : {} ", ex.getMessage());
           } catch (final Exception ex) {
               log.warn("Failed to create dataspace, cause : {}", ex.getMessage());
           }
       }

4. Sidecar container
   
    - Wait for the readiness check of the main container to pass and then execute the script to create a dataspace.

References

https://docs.spring.io/spring-boot/docs/current/api/org/springframework/boot/context/event/ApplicationReadyEvent.html

https://kubernetes.io/docs/concepts/workloads/pods/init-containers/