Reindex UI

[markwalkom]

Now that we have this, I am thinking a UI that allows users to specify things like the below would be an awesome way to improve the UX.

It'd contain a page with things like;

1. Host (default to localhost) - mandatory
2. Source + destination index names - mandatory
   1. Optional settings like size etc
3. A script editor - optional
4. Any of the other settings - optional

And then (ideally), a section on the same page that shows the status of any existing reindex jobs, along with a cancel button.

[chakrayadavalli]

+1

[kobelb]

/cc @elastic/kibana-management

[cjcenizal]

We're planning on implementing a Reindex Wizard in Index Management which will address these needs. Users can click a "Reindex data" button, or select indices in Index Management and choose a "Reindex data from indices" option, or select a single index and choose "Reindex data into index". Here's a mockup of what we have in mind:

[cjcenizal]

Note that the list of running reindex tasks is a subset of the Tasks UI functionality (#42621). We should share this code as much as possible, e.g. exported components, services, hooks, de/serializers.

[cjcenizal]

A core use case for reindexing is to fix mappings with the original data. This workflow consists of two parts:

1. Create a new index with the desired mappings
2. Reindex data into the new index

If I were using this wizard, I'd like to answer a few questions and perform a few actions:

1. What will the resulting mappings be in my destination index? This would be an aggregation of the existing mappings in that index plus any mappings in the source indices which aren't defined by the destination index.
2. How can I choose the right destination index? As I select a destination index, I would want to see how many documents it contains, number of fields, date created, and any other metadata that will inform my choice. I'd also like to be able to easily choose a destination index and preview its mappings. If I've picked the wrong index I want to be able to easily choose another one.
3. If I select a bunch of source indices and then realize my destination index doesn't have the mappings I want, what's the easiest way for me to create that index without losing my work? Can we link out to a "Create index" form an link back to this wizard without losing state?
4. Can the wizard create a destination index automatically for me?
5. Can I queue up multiple reindexing tasks at once?
6. Can I throttle the reindexing rate?
7. Can I switch the source index's alias to the destination index once the reindex is complete, to ensure zero downtime?

[cjcenizal]

Closing in favor of #46755