Here are a few terms used throughout the DataStax Zero Downtime Migration documentation and code.
An optional testing phase in which reads are sent to both Origin and Target, enabling you to check that the intended Target of your migration can handle the full workload of reads and writes before finalizing the migration and moving off the ZDM Proxy instances. For details, see Enable asynchronous dual reads.
Cassandra Query Language (CQL) is a query language for the Cassandra database. It includes DDL and DML statements. For details, see the CQL quick reference.
ZDM Proxy handles your client application’s real-time write requests and forwards them to two Cassandra-based clusters (Origin and Target) simultaneously. The dual-write logic in ZDM Proxy means that you do not need to modify your client application to perform dual writes manually during a migration: ZDM Proxy takes care of it for you. See the diagram in the workflow introduction.
Your existing Cassandra-based cluster, whether it’s open-source Apache Cassandra®, DataStax Enterprise (DSE), or Astra DB.
The cluster that is currently considered the "primary" source of truth. While writes are always sent to both clusters, the primary cluster is the one to which all synchronous reads are always sent, and their results are returned to the client application. During a migration, Origin is typically the primary cluster. Near the end of the migration, you’ll shift the primary cluster to be Target.
Generally speaking, a proxy is a software class functioning as an interface to something else. The proxy could interface to anything: a network connection, a large object in memory, a file, or some other resource. A proxy is a wrapper or agent object that is being called by the client to access the real serving object behind the scenes. In our context here, see ZDM Proxy.
The new cluster to which you want to migrate client applications and data with zero downtime.
An Ansible-based tool that allows you to deploy and manage the ZDM Proxy instances and associated monitoring stack. To simplify its setup, the suite includes the ZDM Utility. This interactive utility creates a Docker container acting as the Ansible Control Host. The Ansible playbooks constitute the ZDM Automation.
An open-source component designed to seamlessly handle the real-time client application activity while a migration is in progress.