Client Changes in Fluid Server Cluster Discovery Feature

[tianzhu007]

To implement Fluid Server Cluster discovery, we need to add the following changes to the Client side:

1. New interface (ISession): Used to store the Fluid server cluster’s URLs and session alive flag. This session information will be returned by the discovery call in create session and join session flow. This interface would be deleted and be consumed from service-client package later, once the server-side code is checked-in.
2. New API to get session information in the driver side: A GET API is called during the join flow to return the correct session information to the client. This api will return the session information if there is an existing session and will create a session and update the session information and then return the session details if there is no live session.
3. The discoveryEndpoint URL and the enableDiscovery flag will let the driver know if the current workflow needs discovery or not.
4. We added the noCacheGitManager for historian. When the client creates a new session, we bypass the cache and fetch the summary from storage, and then update the cache. Otherwise, the client might read an outdated summary from a cache in the old cluster. For example:
   • Client A opens a document in the US, generates some ops and closes the session. The final summary with the sequence # 20 is cached.
   • Client B then opens the same document and creates a session in the EU, generates some ops, and closes the session. The final summary with the sequence # 30 is cached in EU.
   • Client A reopens the document from the US and a new session is created. If we do not disable the cache, client A reads the summary with the summary sequence number of 20 which would be incorrect. Therefore, we need to let client A read the summary directly from the storage, instead of the cache, and update the cache with the fetched summary (sequence number 30).

[tianzhu007]

    return new socketStorage.DocumentStorageService(

(nit) include parameter names for a better readability?

Refers to: packages/drivers/local-driver/src/localDocumentService.ts:42 in 626fa4e. [](commit_id = 626fa4e, deletion_comment = False)

This is to create a new service based on the existing constructor. We can open the documentStorageService.ts to read the parameter names.

[tianzhu007]

    return new socketStorage.DocumentStorageService(

(nit) include parameter names for a better readability?

Refers to: packages/drivers/local-driver/src/localDocumentService.ts:42 in 626fa4e. [](commit_id = 626fa4e, deletion_comment = False)

I am unable to add the parameter names when creating this object. Based on https://stackoverflow.com/questions/45507428/typescript-create-class-via-constructor-passing-in-named-parameters, we need to rewrite the constructor to realize it. We can keep it as it is right now. :)