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Modifying a Cluster with Zodan

Zodan provides tools to add or remove a node with zero downtime. The scripts are located in the samples/Z0DAN directory of the Spock GitHub repository.

During node addition, Zodan seamlessly manages creation of the new node, subscription management (both to and from the node), replication slot creation, data synchronization, replication slot advancement, and final activation of subscriptions.

During node removal, Zodan simplifies removing fully-functional or failed nodes from a cluster. When you remove a node from a cluster, the removal does not delete Postgres artifacts (the database, data directory, log files, etc.).

Hint

Zodan simplifies removing partially added nodes created during failed node add operations. Additional cleanup steps may be required before attempting another node deployment on the target host.

Note

Each script must be run from the target node being added or removed.

Zodan Use Cases

The following table describes when to use the Python scripts versus the SQL scripts:

Use Case Use zodan.py & zodremove.py Use zodan.sql & zodremove.sql
CLI automation or scripting Good
SQL-only environments Good
No Python or shell access Good
Postgres extension workflows Good Good

Key Differences Between using Zodan and the Manual Process

The following differences highlight how Zodan automates and simplifies node addition:

  • Zodan stores sync LSNs and uses them later to ensure subscriptions start from the correct point even if hours pass between steps.

  • Zodan automatically detects existing schemas on n4 and populates the skip_schema parameter, preventing conflicts during structure sync.

  • Zodan verifies all nodes run the same Spock version before starting.

  • Zodan includes the verify_subscription_replicating() function after enabling subscriptions to ensure they reach replicating status.

  • Zodan handles 2-node scenarios differently. No disabled subscriptions are needed when adding to a single-node cluster.

  • Zodan shows final status of all nodes and subscriptions across the entire cluster, not just the new node.

For more information, review the following resources: