Add Index Alias management capabilities

[pierrelambert]

The Alias capability of Indexes with ft.aliasadd, ft.aliasdel, FT.ALIASUPDATE permits agility in making index and apps evolving.
Would be nice to be able to handle this at SearchIndex level directly.

[tylerhutcherson]

@pierrelambert 100% Agreed - this is planned for the 0.3.0 release. Though it gets tricky without the ability to list which aliases are used per index.

Ideally the index alias would be a schema property like this:

index:
  name: users_v1
  prefix: user
  alias: users

fields:
    - name: user
      type: tag
    - name: credit_score
      type: tag

So then the alias would get added transparently as they call index.create(...)

And then a new command to update the alias:

index.update_alias("new_alias_name")

However, given we can't trace the state of the index<>alias relationships... this is pretty much impossible without footguns all over the place.

@bsbodden curious on your take?

[pierrelambert]

Define / Set an alias to an index is must have.
Change the index an alias is referring to (FT.ALIASUPDATE) is must have too

[bsbodden]

I agree with @pierrelambert that this is a must have for prod environments, since the index to alias relationship is a one-to-many we could:

• take a list of strings under aliases or a single string under alias
• We can use FT.INFO alias to determine if the alias exists and also use index_name to verify that it is attached to the current index
• Keep/manage our own per-index Redis SET of aliases (something like [index_name]_ALIASES) until a command to retrieve aliases is provided (FT._LIST_ALIASES index)
• Using a set this way is a very common pattern in Redis libraries, we just need to make sure we clean up after ourselves when/if the index is deleted

[tylerhutcherson]

I like this approach. I’ve been hesitant to create extra “metadata” generated by the library… but I think I agree that usability and functionality is most important here. We need alias support for sure.

I’ll start working on a more detailed write up for this.