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Node DNS names in Azure Cosmos DB for PostgreSQL

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APPLIES TO: Azure Cosmos DB for PostgreSQL (powered by the Citus database extension to PostgreSQL)

When an Azure Cosmos DB for PostgreSQL cluster is provisioned, every node is assigned its own fully qualified domain name (FQDN). This FQDN is used to connect to each node provided proper network security was set up to grant access. The FQDN is used in the Postgres connection string whether private or public access is used.

Domain names in Azure Cosmos DB for PostgreSQL

All node domain names in Azure Cosmos DB for PostgreSQL are created in postgres.cosmos.azure.com domain. A node's FQDN is created in the following format

<node-qualifier>-<cluster-name>.<uniqueID>.postgres.cosmos.azure.com

where node-qualifier can be 'c' for coordinator or 'w0', 'w1', etc. for worker nodes; cluster-name is the name for the cluster you selected during cluster provisioning; uniqueID is a randomly generated globally unique 14-character identifier.

For instance: c-mycluster.12345678901234.postgres.cosmos.azure.com.

This FQDN is resolved into a public IP for each node in the cluster. If public access is enabled on the cluster, this FQDN is used in the Postgres connection string to connect to a node.

When you enable private access on the cluster, Azure creates a private DNS zone for each cluster. FQDN for each node with a private endpoint is created in this private DNS zone in addition to its primary FQDN. FQDN in this private DNS zone uses the following format

<node-qualifier>-<cluster-name>.<uniqueID>.privatelink.postgres.cosmos.azure.com

where node-qualifier can be 'c' for coordinator or 'w0', 'w1', etc. for worker nodes; cluster-name is the name for the cluster you selected during cluster provisioning; uniqueID is a randomly generated globally unique 14-character identifier.

For instance: c-mycluster.12345678901234.privatelink.postgres.cosmos.azure.com.

node-qualifier-cluster-name.uniqueID.postgres.cosmos.azure.com FQDN can be used from within a virtual network (VNet) environment too. If DNS name resolution is performed from within a VNet, FQDN resolves into a private IP assigned to a node via a private endpoint. If DNS name resolution is done from the public Internet, FQDN resolves into a public IP assigned to that node.

It's important to use only FQDN to access a node as assigned public IP addresses may change during normal operations such as an HA failover or compute scaling operation.

Important

Azure Cosmos DB for PostgreSQL clusters created before June 6th, 2023 use the following legacy domain name and FQDN format:

Primary FQDN format: node-qualifier.cluster-name.postgres.database.azure.com FQDN in a private DNS zone: node-qualifier.privatelink.cluster-name.postgres.database.azure.com

where node-qualifier is 'c' for coordinator and 'w0', 'w1', etc. for worker nodes and cluster-name is the name for the cluster you selected during cluster provisioning.

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