Improve error messages in ES administration

Summary

This is a follow-up to !17230 (closed) / !18254 (merged) / !20421 (merged).

Currently the ES administration only implements some basic error handling for ES connection failures when creating/deleting indices, and shows them as a general validation error rather than next to the form fields with the faulty value(s).

Some information about the error data we get from ES and other involved gems:

• The ES gem gives us exceptions based on the different HTTP statuses, e.g. types like Elasticsearch::Transport::Transport::Errors::NotFound for a 404: https://github.com/elastic/elasticsearch-ruby/blob/v5.0.3/elasticsearch-transport/lib/elasticsearch/transport/transport/errors.rb#L19-L63
• The ES exception messages look like this:

  [404] {"error":{"root_cause":[{"type":"index_not_found_exception","reason":"no such index","resource.type":"index_or_alias","resource.id":"gitlab-development-v12p1","index_uuid":"_na_","index":"gitlab-development-v12p1"}],"type":"index_not_found_exception","reason":"no such index","resource.type":"index_or_alias","resource.id":"gitlab-development-v12p1","index_uuid":"_na_","index":"gitlab-development-v12p1"},"status":404})

  • ES itself returns details in structured JSON, but the ES gem combines all of it into one string with the format [$HTTP_STATUS] $JSON_BODY. This message could be parsed to identify more details.
• Some general connection errors are returned by the Faraday gem (which is the HTTP client the ES gem uses), with e.g. a type like Faraday::ConnectionFailed and a message like:

  (Connection refused - Connection refused - connect(2) for "localhost" port 9201 (localhost:9201))

Improvements

It's not clear yet which error cases could benefit most from more user-friendly error messages.

The main thing we noticed is that it would be helpful to identify which form fields are to blame for connection errors, so we could show a validation error next to the relevant urls or AWS fields.

Involved components

• ee/app/assets/javascripts/elasticsearch/
• ee/app/services/elastic/create_index_service.rb
• ee/app/services/elastic/destroy_index_service.rb
• ee/lib/api/elasticsearch_indices.rb