Impl. Proposal for Merging of Subscriptions ( Positive Scenarios )

References

CPS-1870 - Getting issue details... STATUS

Assumptions

Issues & Decisions

Overview

This page only contains the details used for starting the development on the Merging of Subscriptions use case. Just the straight forward scenarios will be covered and the overall solution will be build on top of it.

Schema Definitions

1. DME to NCMP Subscription Request
   
   

   DME to NCMP Subscription Request Expand source

   Header values ( all cloud events header )
   
   
   {
     "data": {
       "subscriptionId": "unique subscription id",
       "predicates": [
   	{
           “targets” :  list of cmhandles
           "datastore": “ncmp-datastore:passthrough-operational or ncmp-datastore:passthrough-running",
           "datastore-xpath-filter": list of valid xpaths
     
       }
   	]
   }

2. NCMP to DMI-Plugin Subscription Request
   
   

   NCMP to DMI-Plugin Subscription Request Expand source

   // correlationId for tracking
   {
     "data": {
      
   	"cmhandles" : [
   	{
   		"cmHandleId": "cmhandle1",
   		"private-properties": {...} 
   	},
   	{
   		"cmHandleId": "cmhandle2",
   		"private-properties": {...}
   	},
   	{
   		"cmHandleId": "cmhandle3",
   		"private-properties": {...}
   	}
   	]
       "predicates": [
   	{
           “targets” :  [“cmHandle1”, “cmHandle2”, "cmhandle3"]
           "datastore": “ncmp-datastore:passthrough-operational",
           "datastore-xpath-filter": ["p1/c1", "p2/c2"]
     
       },
   	{
           “targets” :  [“cmHandle1”]
           "datastore": “ncmp-datastore:passthrough-running",
           "datastore-xpath-filter": ["p3/c3", "p4/c4"]
       }
   	]
   }

3. DMI-Plugin to NCMP Subscription Response
   
   

   DMI-Plugin to NCMP Subscription Response Expand source

   Headers will have relevant fields including the subscriptionId
   
   // correlationId for tracking - to link with NCMP. ( get clarity )
   { 
   "data" : {
   
      "dmiName":"<dmiName>", 
      "statusCode": "1", // open issue for the status codes ( whether to use the same for DMI to NCMP  as for NCMP to Clients)
      "statusMessage" : "accepted/rejected"
   }
   }

4. NCMP to DME Subscription Response
   
   

   NCMP to DME Subscription Response Expand source

   Headers will have relevant fields including the subscriptionId
   
   {
     "data": {
   		"subscriptionId": "sample-subscription-id",
   		"accepted-targets" : ["ch-1", ...],
   		"rejected-targets" : ["ch-1", ...],
   		"pending-targets" : ["ch-1", ...],
     }
   }

Storage Solutions

Proposed Data Storage

Use a combination of

1. Database (yang modelled) for permanent subscription details, subscribers, predicates
2. In-Memory (hazelcast) for transient subscription details:  state (acceptep, rejected, pending)

Example Flow 1: First Subscription

• We have the below configuration managed by CPS-NCMP
  
  

  #	cmhandle	dmi-plugin
  1	ch-1	dmi-1
  2	ch-2	dmi-1
  3	ch-3	dmi-2
  4	ch-4	dmi-2
  5	ch-5	non-responding-dmi

1. We get a Subscription Create Request with unique subscription-id and a list of predicates(list of targets , datastore and list of filters)
   
   

   Subscription Create Message Expand source

   {
   "subscriptionId" : "A-10",
   "predicates" : [
     {
       "targets": [ch-1,ch-2],
       "datastore" : "ncmp-datastore:passthrough-operational",
       "datastore-xpath-filter" : ["p1/c1","p2/c2"]
       },
     { "targets": [ch-3],
       "datastore" : "ncmp-datastore:passthrough-operational",
       "datastore-xpath-filter" : ["p3/c3"]
       }
   ] 
   }

   
   

2. We persist the incoming request as is in our persistent store using a relevant subscription model ( this model also needs to be revised )

3. We also maintain a distributed datastructure in Hazelcast to keep track of the request and response to the client.
   
   

   SubscriptionId	dmi-plugin	affectedCmHandles	status
   A-10	dmi-1	["ch-1","ch-2"]	PENDING
   A-10	dmi-2	["ch-3"]	PENDING

4. Read the requests from the distributed data structure and form the request for the DMI-Plugin and publish it to the internal kafka channel.
5. If the DMI-Plugin responds back within the configured time , so the request will either be ACCEPTED or REJECTED.
   1. if whole subscription request is ACCEPTED , update the distributed data structure and then store the subscription to the ActiveSubscriptions in cps-cache.
   2. if whole subscription request is REJECTED , update the distributed data structure and send back the response to the client.

   3. if the DMI Plugin fails to respond then the status would remain PENDING only as there is no change.
      
      

      SubscriptionId	dmi-plugin	affectedCmHandles	status
      A-10	dmi-1	["ch-1","ch-2"]	ACCEPTED
      A-10	dmi-2	["ch-3"]	REJECTED

      
      If there are no more PENDING requests , then we can right away send the response without updating the cache.

6. We store the "ActiveSubscriptions" using a new model which will look like below.
   
   

   SubscriptionId	cmHandle	filter	datastore
   A-10	ch-1	p1/c1	ncmp-datastore:passthrough-operational
   A-10	ch-1	p2/c2	ncmp-datastore:passthrough-operational
   A-10	ch-2	p1/c1	ncmp-datastore:passthrough-operational
   A-10	ch-2	p2/c2	ncmp-datastore:passthrough-operational

7. Now based on whatever we have in the distributed map , we will send the response to the clients and may be clear the in-memory structure if required.

Example Flow 2: Second Subscription (merge)

1. We get a new subscription create request.
   
   

   2nd Subscription Create Message Expand source

   {
   "subscriptionId" : "B-52",
   "predicates" : [
     {
       "targets": [ch-2],
       "datastore" : "ncmp-datastore:passthrough-operational",
       "datastore-xpath-filter" : ["p2/c2" , "p3/c3"]
       }
   ]
   }

   
   

2. We now look at the "ActiveSubscriptions"  if we already have an active subscription either for a combination of "cmhandle and xpath filter and the datastore".
   
   Current view of ActiveSubscriptions
   
   

   SubscriptionId	cmHandle	filter	datastore
   A-10	ch-1	p1/c1	ncmp-datastore:passthrough-operational
   A-10	ch-1	p2/c2	ncmp-datastore:passthrough-operational
   A-10	ch-2	p1/c1	ncmp-datastore:passthrough-operational
   A-10	ch-2	p2/c2	ncmp-datastore:passthrough-operational

   Check if we have ch-2 , p2/c2 and ncmp-datastore:passthrough-operational then directly add to the ActiveSubscription. Similarly check for ch-3 , p3/c3 and ncmp-datastore:passthrough-operational ( which in this case will not be directly to the active subscription)

   
   

3. Now the state of ActiveSubscription is :
   
   

   SubscriptionId	cmHandle	filter	datastore
   A-10	ch-1	p1/c1	ncmp-datastore:passthrough-operational
   A-10	ch-1	p2/c2	ncmp-datastore:passthrough-operational
   A-10	ch-2	p1/c1	ncmp-datastore:passthrough-operational
   A-10	ch-2	p2/c2	ncmp-datastore:passthrough-operational
   B-52	ch-2	p2/c2	ncmp-datastore:passthrough-operational

   and state of the in-memory data structure is as follows.
   
   

   SubscriptionId	dmi-plugin	affectedCmHandles	status
   B-52	dmi-1	["ch-2"]	PENDING

4. Now we send the request to DMI plugin (dmi-1) with just the private properties of the ch-2 with the delta xpath.
   
   1. DMI Plugin could either apply the whole subscription request or reject the whole subscription. i.e respond with accepted/rejected

5. Based on the response from DMI plugin the in-memory structure is updated and response is sent back to the clients.
   
   if DMI says it is accepted then : 

   SubscriptionId	dmi-plugin	affectedCmHandles	status
   B-52	dmi-1	["ch-2"]	ACCEPTED

   
   if DMI says it is rejected then : 

   SubscriptionId	dmi-plugin	affectedCmHandles	status
   B-52	dmi-1	["ch-2"]	REJECTED

   
   if we get no response within the configured time then :

   SubscriptionId	dmi-plugin	affectedCmHandles	status
   B-52	dmi-1	["ch-2"]	PENDING

   
   But we still send some response within the pre-configured time.
   
   
   

6. if the above request was accepted then we should add it to the list of "ActiveSubscriptions" as well.
   
   

   SubscriptionId	cmHandle	filter	datastore
   A-10	ch-1	p1/c1	ncmp-datastore:passthrough-operational
   A-10	ch-1	p2/c2	ncmp-datastore:passthrough-operational
   A-10	ch-2	p1/c1	ncmp-datastore:passthrough-operational
   A-10	ch-2	p2/c2	ncmp-datastore:passthrough-operational
   B-52	ch-2	p2/c2	ncmp-datastore:passthrough-operational
   B-52	ch-2	p3/c3	ncmp-datastore:passthrough-operational

7. If the status was accepted/rejected then after sending the response to the client we can clear the in-memory structure for subscriptionId B-52.