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From GitBox <...@apache.org>
Subject [GitHub] [incubator-openwhisk] rabbah commented on a change in pull request #4314: CosmosDB Cache Invalidation Service
Date Wed, 20 Mar 2019 15:29:05 GMT
rabbah commented on a change in pull request #4314: CosmosDB Cache Invalidation Service
URL: https://github.com/apache/incubator-openwhisk/pull/4314#discussion_r267392081
 
 

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 File path: core/cosmosdb/cache-invalidator/README.md
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+# OpenWhisk Cache Invalidator Service
+
+This service performs cache invalidation in OpenWhisk cluster to enable cache event propagation
in multi region setups.
+
+## Design
+
+OpenWhisk cluster uses a Kafka topic `cacheInvalidation` to communicate changes to any cached
entity. Messages on this
+topic are of the form
+
+```json
+{"instanceId":"controller0","key":{"mainId":"guest/hello"}}
+```
+
+When deploying multiple seprate cluster of OpenWhisk which do not share same Kafka instance
we would need a way to
+propagate the cache change event across cluster. For CosmosDB based setups this can be done
by using [CosmosDB ChangeFeed][1]
+support. It enables reading changes that are made to any specific collection.
+
+This service makes use of [change feed processor java][2] library and listen to changes happening
in `whisks` and `subject`
+collection and then convert them into Kafka message events which can be sent to `cacheInvalidation`
topic of local cluster
 
 Review comment:
   collection -> collections.

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