elasticsearch_reindex.rb

es_alias  = ENV.fetch('ALIAS')
hosts     = ENV.fetch('HOSTS')
old_index = ENV.fetch('OLD_INDEX')
old_type  = ENV.fetch('OLD_TYPE')
new_index = ENV.fetch('NEW_INDEX')
new_type  = ENV.fetch('NEW_TYPE')
size      = ENV.fetch('SCAN_SIZE', 100)

client = Elasticsearch::Client.new(hosts: hosts)
unless client.indices.exists(index: new_index)
  body = { mappings: JSON.parse("PATH/TO/MAPPING.JSON") }
  client.indices.create(index: new_index, body: body)
end

current_count = client.count(index: old_index)
puts "We will be copying #{current_count["count"]} documents from '#{old_index}' into '#{new_index}'"

# Fill up the new index with old index data.
# This currently does a match_all.
response = client.search(index: old_index, type: old_type, search_type: 'scan', scroll: '5m', size: size)
while (response = client.scroll(scroll_id: response['_scroll_id'], scroll: '5m')) do
  break if response['hits']['hits'].empty?
  body = response['hits']['hits'].map do |document|
    {
      index: {
        _index: new_index,
        _type:  new_type,
        _id:    document['_id'],
        data:   document['_source']
      }
    }
  end
  client.bulk(body: body)
  printf('.')
end

# You may wish to change this to be the last scroll id if you are running multiple scrolls!
client.clear_scroll(scroll_id: %w(_all))

puts
puts "Updating alias #{es_alias} to point from '#{old_index}' to '#{new_index}'"
body = {
  actions: [
    { remove: { index: old_index, alias: es_alias } },
    { add:    { index: new_index, alias: es_alias } }
  ]
}
client.indices.update_aliases(body: body)