Rebuild elasticsearch index with zero downtime

elasticsearch.rake

require 'elasticsearch/rails/tasks/import'

namespace :elasticsearch do
  desc 'Rebuild index with zerodown time'
  task rebuild: :environment do
    size = (ENV['size'].presence || 1000).to_i
    model = ENV['model'].to_s.classify.constantize
    delete_old_index = ENV['delete'].present?
    es = model.__elasticsearch__

    count = 0
    total = model.count
    origin_index_name = model.index_name
    new_index_name = "#{origin_index_name}_#{Time.current.strftime('%Y%m%d%H%M%S')}"

    model.find_in_batches(batch_size: size) do |group|
      actions = group.map do |record|
        count += 1
        puts "Import #{model} to #{new_index_name} #{count}/#{total}"
        { index: { _id: record.id, data: record.as_indexed_json } }
      end

      es.client.bulk(
        index: new_index_name,
        type: model.document_type,
        body: actions
      )
    end

    old_indices = begin
      es.client.indices.get_alias(name: origin_index_name).keys
    rescue Elasticsearch::Transport::Transport::Errors::NotFound
      {}
    end

    actions = old_indices.map do |old_index_name|
      { remove: { index: old_index_name, alias: origin_index_name } }
    end

    actions << { add: { index: new_index_name, alias: origin_index_name } }

    es.client.indices.update_aliases(body: { actions: actions })

    puts "Alias #{new_index_name} to #{origin_index_name}"

    next unless delete_old_index
    old_indices.each do |old_index_name|
      puts "Delete #{old_index_name}"
      es.client.indices.delete(index: old_index_name)
    end
  end
end

bundle exec rake elasticsearch:rebuild model=post # rebuild index
bundle exec rake elasticsearch:rebuild model=post delete=true # rebuild index and delete old index