In order to improve the experience of cross-cluster search, we are changing
the default value of the remote cluster `skip_unavailable` setting from `false` to `true`.
This setting causes any cross-cluster _search (or _async_search) to entirely fail when
any remote cluster with `skip_unavailable=false` is either unavailable (connection to it fails)
or if the search on it fails on all shards.
Setting `skip_unavailable=true` allows partial results from other clusters to be
returned. In that case, the search response cluster metadata will show a `skipped`
status, so the user can see that no data came in from that cluster. Kibana also
now leverages this metadata in the cross-cluster search responses to allow users
to see how many clusters returned data and drill down into which clusters did not
(including failure messages).
Currently, the user/admin has to specifically set the value to `true` in the configs, like so:
```
cluster:
remote:
remote1:
seeds: 10.10.10.10:9300
skip_unavailable: true
```
even though that is probably what search admins want in the vast majority of cases.
Setting `skip_unavailable=false` should be a conscious (and probably rare) choice
by an Elasticsearch admin that a particular cluster's results are so essential to a
search (or visualization in dashboard or Discover panel) that no results at all should
be shown if it cannot return any results.
* New docs structure for remote clusters
* Fix broken cross-book link errors
* More broken cross-book link errors
* Remove redirects for new pages
* Link to generic remote cluster docs instead
* Drop 'API' from the abbreviated title
* Add 'Establish trust with a remote cluster' section
* Restructure 'Establish trust' section into Prprequisite/local/remote instructions
* Add 'Configure roles and users' section
* Add 'Connect to a remote cluster' section
* Move version compatibility to prerequisites
* Fix test errors
* Incorporate review feedback
* Mention version 8.10 or later in the intro for API keys
* Add license prerequisite
* [DOCS] Update remote cluster docs
* Add files, rename files, write new stuff
* Plethora of changes
* Add test and update snippets
* Redirects, moved files, and test updates
* Moved file to x-pack for tests
* Remove older CCS page and add redirects
* Cleanup, link updates, and some rewrites
* Update image
* Incorporating user feedback and rewriting much of the remote clusters page
* More changes from review feedback
* Numerous updates, including request examples for CCS and Kibana
* More changes from review feedback
* Minor clarifications on security for remote clusters
* Incorporate review feedback
Co-authored-by: Yang Wang <ywangd@gmail.com>
* Some review feedback and some editorial changes
Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
Co-authored-by: Yang Wang <ywangd@gmail.com>
