restore_latest_backup_to_debug_database_job.rb

class RestoreLatestBackupToDebugDatabaseJob < ActiveJob::Base                                                                                                                                                                                
  queue_as :default

  def perform
    # Open the S3 bucket
    bucket = Aws::S3::Resource.new.bucket(ENV.fetch('PGBACKUPS_BUCKET'))

    # Get the key of the latest backup
    Rails.logger.info "Determining the latest backup"
    backup_key = key_of_latest_backup(bucket)

    # Download and write to a temporary file
    backup_path = "#{Dir.tmpdir}/backup_#{backup_key.split('/')[-1]}"
    Rails.logger.info "Downloading backup #{backup_key} to #{backup_path}"
    bucket.object(backup_key).get(response_target: backup_path)

    # Import the dump into the debug database
    host = ENV.fetch('DEBUG_DB_HOST')
    port = ENV.fetch('DEBUG_DB_PORT')
    username = ENV.fetch('DEBUG_DB_USERNAME')
    database = ENV.fetch('DEBUG_DB_DATABASE')
    password = ENV.fetch('DEBUG_DB_PASSWORD')
    restore_cmd = "PGPASSWORD=#{password} pg_restore --verbose --clean --no-acl --no-owner -h #{host} -p #{port} -U #{username} -d #{database} #{backup_path}"
    Rails.logger.info "Restoring the backup: #{restore_cmd}"
    system restore_cmd
  end

  private

  def key_of_latest_backup(bucket)
    # First we get only the metadata of all backups and we select the one that was modified most recently.
    latest_object_summary = nil
    bucket.objects(prefix: "DIRECTORY").each do |object_summary|
      if latest_object_summary.nil? || latest_object_summary.last_modified < object_summary.last_modified
        latest_object_summary = object_summary
      end
    end

    # Raise an error if the backup is older than a week ago. Then we have a problem.
    if latest_object_summary.last_modified < 1.week.ago
      raise "The last database backup is from #{latest_object_summary.last_modified}, which is more than a week ago."
    end

    # Returns its key
    return latest_object_summary.key
  end
end