How to Add Standby Nodes to PostgreSQL Database Clusters

Validated on 8 Aug 2019 • Last edited on 23 May 2024 ha | standby node | read-only node

PostgreSQL is an open source, object-relational database built for extensibility, data integrity, and speed. Its concurrency support makes it fully ACID-compliant, and it supports dynamic loading and catalog-driven operations to let users customize its data types, functions, and more.

In a database cluster, standby nodes maintain a copy of the primary node. If the primary node fails, a standby node is automatically promoted to replace it.

Clusters can have up to two standby nodes. At least one standby nodes is necessary for a high availability cluster configuration.

Note

Standby nodes differ from read-only nodes, which provide geographically distinct horizontal read scaling.

You can add standby nodes during cluster creation in the cluster configuration section of the create page.

You can also add standby nodes to an existing database cluster. From the Databases page, click the name of the cluster to go to its Overview page, then click the Settings tab.

On the Settings page, in the Cluster configuration section, click Edit. Open the Standby Nodes dropdown and choose the number of standby nodes.

Note

Due to the memory requirements of replication, standby nodes are only supported for plans with 2GB of RAM or more.

When you’re done, click Save to immediately provision the standby nodes. The time to complete varies depending on the size of the primary node and its data, but we recommend allowing at least 5 minutes.

Use Standby Nodes for Reads

You can also use standby nodes for reads, to improve your cluster’s performance. However, doing so can result in the standby nodes being too overwhelmed to properly replace the primary node in case of failure.

To use standby nodes for reads, you can find the standby nodes’ hostname via the API.

How to retrieve an existing database cluster using the DigitalOcean API

To retrieve an existing database cluster using the DigitalOcean API, follow these steps:

Create a personal access token, and save it for use with the API.

Send a GET request to https://api.digitalocean.com/v2/databases/{database_cluster_uuid}

cURL

To retrieve an existing database cluster with cURL, call:


                curl -X GET \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $DIGITALOCEAN_TOKEN" \
  "https://api.digitalocean.com/v2/databases/9cc10173-e9ea-4176-9dbc-a4cee4c4ff30"

Go

Go developers can use Godo, the official DigitalOcean V2 API client for Go. To retrieve an existing database cluster with Godo, use the following code:


                import (
    "context"
    "os"

    "github.com/digitalocean/godo"
)

func main() {
    token := os.Getenv("DIGITALOCEAN_TOKEN")

    client := godo.NewFromToken(token)
    ctx := context.TODO()

    cluster, _, err := client.Databases.Get(ctx, "9cc10173-e9ea-4176-9dbc-a4cee4c4ff30")
}

Python


                import os
from pydo import Client

client = Client(token=os.environ.get("DIGITALOCEAN_TOKEN"))

get_resp = client.databases.get_cluster(database_cluster_uuid="a7a89a")

And you can find the standby nodes’ IP addresses by querying DNS. For example:

dig +short A replica-db-redis-tutorial-redis-watch-local-do-user-0.c.db.ondigitalocean.com
123.45.67.89
123.456.78.901

Traffic you send to multiple standby nodes is not load balanced. In order to load balance this traffic, you can either use a client that does it natively or look up the IPs with a tool such as dig.

How to Add Standby Nodes to PostgreSQL Database Clusters

Use Standby Nodes for Reads

cURL

Go

Python

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