FQDNs of PostgreSQL hosts

To connect to a host, you need its fully qualified domain name (FQDN). You can use the FQDN of a particular host in the cluster or a special FQDN always pointing to the current master host or the most recent replica.

Here is a host FQDN example:

rc1a-goh2a9tr********.mdb.yandexcloud.net

Getting a host FQDNGetting a host FQDN

There are several ways to get a PostgreSQL host's FQDN:

• Look up the FQDN in the management console:

  1. Navigate to the cluster page.
  2. Navigate to Hosts.
  3. Copy the Host FQDN column value.

• In the management console, copy the cluster connection command (it contains the host’s FQDN). To get this command, navigate to the cluster page and click Connect.

• Get the list of cluster hosts using the CLI or API.

Special FQDNsSpecial FQDNs

Managed Service for PostgreSQL provides the following special FQDNs:

• Current master FQDN
• FQDN of the most recent replica

In multi-host clusters, special FQDNs may temporarily point to the old host, even if it has switched its role (e.g., from master to replica). If using a special FQDN which points to the current master, some write requests may fail if routed to the replica. This is because it takes time to update DNS records for special FQDNs. If your write request returns an error, repeat it later.

Current masterCurrent master

An FQDN in c-<cluster_ID>.rw.mdb.yandexcloud.net format always points to the current master host in the cluster. You can get the cluster ID from the folder’s cluster list.

When connecting to this FQDN, you can perform read and write operations.

Most recent replicaMost recent replica

An FQDN in c-<cluster_ID>.ro.mdb.yandexcloud.net format points to the replica that is most up-to-date with the current master. You can get the cluster ID with the list of clusters in the folder.

Specifics:

• When connecting to this FQDN, you can only perform read operations.
• If there are no active replicas in the cluster, this FQDN will point to the current master host.
• Replicas with a manually configured replication source cannot be selected as most up-to-date replicas when using this FQDN.

AliasesAliases

With aliases, you can access the master, most recent replica, or each particular host of your Managed Service for PostgreSQL cluster using a stable, human-readable name no matter what their internal FQDNs are. Aliases are user-defined and can be used alongside regular and special FQDNs.

Cluster aliasCluster alias

A cluster alias always points to the current master host in the Managed Service for PostgreSQL cluster. It has the following format:

c-<short_name>-pg-<folder_ID>.rw.mdb.yandexcloud.net

Where <short_name> is a name set by the user when creating the alias.

A cluster alias must be unique within the folder. You can assign only one alias per cluster.

With cluster aliases, you can switch workloads from one cluster to another, e.g., after restoring from a backup. To do this, simply reassign the alias to the new cluster, no application-side updates required.

Host aliasesHost aliases

An alias pointing to a specific cluster host has the following format:

h-<host_short_name>-pg-<folder_ID>.mdb.yandexcloud.net

Where <host_short_name> is a name set by the user when creating the host alias.

Each host alias must be unique within the folder. You can assign only one alias per host.

Selecting an FQDN and cluster connection methodSelecting an FQDN and cluster connection method

To connect to a cluster, you can use the following:

• Host FQDNs.
• Special FQDNs.
• Aliases.

If the cluster consists of several hosts, keep in mind that the current master can become a replica at any moment, and vice versa.

Use one of the following methods to connect to the master host with read and write access:

• Connect using the special FQDN pointing to the current master.

  After a master failover, this FQDN may temporarily point to the previous master, now a replica, due to the time required for the DNS record to update.

  Therefore, applications using this FQDN must be designed to handle temporary master unavailability. For example, they should retry write requests after a short delay.

  Connection example

  In this example, we use the c9qash3nb1v9******** cluster ID:

  psql "host=c-c9qash3nb1v9********.rw.mdb.yandexcloud.net \
        port=6432 \
        sslmode=verify-full \
        dbname=<DB_name> \
        user=<username>"
  

• Connect by listing all cluster hosts and specifying target_session_attrs=read-write.

  Connection example

  Here, we list all the cluster’s hosts.

  The host IDs are rc1a-be***.mdb.yandexcloud.net, rc1b-5r***.mdb.yandexcloud.net, and rc1d-t4***.mdb.yandexcloud.net:

  psql "host=rc1a-be***.mdb.yandexcloud.net,rc1b-5r***.mdb.yandexcloud.net,rc1d-t4***.mdb.yandexcloud.net \
        port=6432 \
        sslmode=verify-full \
        dbname=<DB_name> \
        user=<username> \
        target_session_attrs=read-write"
  

Use one of the following methods to connect to the host with read access:

• Connect using a special FQDN pointing to the most up-to-date replica.

  Connection example

  In this example, we use the c9qash3nb1v9******** cluster ID:

  psql "host=c-c9qash3nb1v9********.ro.mdb.yandexcloud.net \
        port=6432 \
        sslmode=verify-full \
        dbname=<DB_name> \
        user=<username>"
  

• Connect by listing all cluster hosts and specifying target_session_attrs=any.

  Connection example

  Here, we list all the cluster’s hosts.

  The host IDs are rc1a-be***.mdb.yandexcloud.net, rc1b-5r***.mdb.yandexcloud.net, and rc1d-t4***.mdb.yandexcloud.net:

  psql "host=rc1a-be***.mdb.yandexcloud.net,rc1b-5r***.mdb.yandexcloud.net,rc1d-t4***.mdb.yandexcloud.net \
        port=6432 \
        sslmode=verify-full \
        dbname=<DB_name> \
        user=<username> \
        target_session_attrs=any"