[[resiliency]]
== Data Resiliency

As data flows through the event processing pipeline, Logstash may encounter
situations that prevent it from delivering events to the configured
output. For example, the data might contain unexpected data types, or
Logstash might terminate abnormally. 

To guard against data loss and ensure that events flow through the
pipeline without interruption, Logstash provides the following data resiliency
features. 

* <<persistent-queues>> protect against data loss by storing events in an
internal queue on disk. 

* <<dead-letter-queues>> provide on-disk storage for events that Logstash is
unable to process. You can easily reprocess events in the dead letter queue by
using the `dead_letter_queue` input plugin.

//TODO: Make dead_letter_queue an active link after the plugin docs are published.

These resiliency features are disabled by default. To turn on these features,
you must explicitly enable them in the Logstash <<logstash-settings-file,settings file>>.
