Dead lettering is done on a best effort basis. The same message might be dead lettered multiple times. If validation on any of the fields fails at subscription creation/updation, the create/update subscription request will fail.

Attributes

• deadLetterTopic (type: String.t, default: nil) - Optional. The name of the topic to which dead letter messages should be published. Format is projects/{project}/topics/{topic}.The Pub/Sub service account associated with the enclosing subscription's parent project (i.e., service-{project_number}@gcp-sa-pubsub.iam.gserviceaccount.com) must have permission to Publish() to this topic. The operation will fail if the topic does not exist. Users should ensure that there is a subscription attached to this topic since messages published to a topic with no subscriptions are lost.
• maxDeliveryAttempts (type: integer(), default: nil) - Optional. The maximum number of delivery attempts for any message. The value must be between 5 and 100. The number of delivery attempts is defined as 1 + (the sum of number of NACKs and number of times the acknowledgement deadline has been exceeded for the message). A NACK is any call to ModifyAckDeadline with a 0 deadline. Note that client libraries may automatically extend ack_deadlines. This field will be honored on a best effort basis. If this parameter is 0, a default value of 5 is used.