# File lib/fog/aws/requests/ecs/describe_container_instances.rb, line 30
        def describe_container_instances(params={})
          response = Excon::Response.new
          response.status = 200

          cluster = params.delete('cluster') || 'default'

          instances_id = params.delete('containerInstances')
          msg = 'ClientException => Container instance cannot be empty.'
          raise Fog::AWS::ECS::Error, msg unless instances_id

          result = []
          [*instances_id].each do |inst|
            if match = inst.match(/^arn:aws:ecs:.+:\d{1,12}:container-instance\/(.+)$/)
              result = self.data[:container_instances].select { |i| i['containerInstanceArn'].eql?(inst) }
            else
              result = self.data[:container_instances].select { |i| i['containerInstanceArn'].match(/#{inst}$/) }
            end
          end

          instances = result
          response.body = {
            'DescribeContainerInstancesResult' => {
              'containerInstances' => instances,
              'failures'           => []
            },
            'ResponseMetadata' => {
              'RequestId' => Fog::AWS::Mock.request_id
            }
          }
          response
        end