Create read replicas

MySQL | PostgreSQL | SQL Server

This page describes how to create a read replica for a Cloud SQL instance.

To set up a Cloud SQL instance to act as a publisher to an externalsubscriber, seeConfigure external replicas.

Important: Before using this feature, reviewAbout replication in Cloud SQL,including theLimitations.

A read replica is a copy of the primary instance that reflects changes to theprimary in almost real time, in normal circumstances. You can use a read replicato offload read requests or analytics traffic from the primary instance.

Additionally, for disaster recovery, you can perform a regional migration. Ifa replica is across-region replica, you can perform a failover to another region;specifically, you can promote a replica to a standalone instance(in which case, existing replicas would not consider that instance as primary).

For more information about how replication works, seeReplication in Cloud SQL.

Before you begin

If you are creating the first replica for this instance, ensure that theinstance meets the requirements for primary instances.Learn more.

Create a read replica

When creating a read replica, keep the following considerations in mind:

You can create a maximum of 8 read replicas per primary instance.
If an edition isn't specified, then Cloud SQL Enterprise edition is the default.
If, when creating a read replica or cascading replica, the primary is an Cloud SQL Enterprise Plus edition instance, then you must indicate the edition and tier you want to use.

The steps for creating a read replica are below.

Note:If the primary instance has a private IP connection and the instance accepts database connections fromCloud SQL Language Connectors only, then you can't create read replicas for the instance.

Console

In the Google Cloud console, go to theCloud SQL Instances page.
Go to Cloud SQL Instances
Find the instance for which you want to create a replica, and then open themore actions menu next to the listing.
SelectCreate read replica.
If you don't see that choice, then the instance is a replica; you can't create a replica of a replica.
In theCustomize your instance section, update settings for your replica. Begin by clickingShow configuration options to display the groups of settings. Then, expand the desired groups to review and customize the settings. ASummary of all the options you select appears on the right. Customizing these settings is optional. Defaults are assigned in every case where no customizations are made.
For more details about each setting, see theAbout instance settings page.
ClickCreate replica.
Cloud SQL creates a backup, if needed, and creates the replica. You are returned to the instance page for the primary.

gcloud

Create the replica:

gcloudsqlinstancescreateREPLICA_NAME\--master-instance-name=PRIMARY_INSTANCE_NAME

You can specify a different tier size using the--tier parameter, if needed.

You can specify a different region using the--region parameter.

If the primary instance has an internal IP address only, then add the--no-assign-ip parameter to the command.

You can add more parameters for other instance settings. To learn more, seegcloud sql instances create.

You must create the replica in the same VPC network as the primary instance. You can also specify anallocated-ip-range-name in that VPC network. If no range is specified, the replica is created in a random range.

Terraform

To create a read replica, use aTerraform resource.

resource "google_sql_database_instance" "read_replica" {  name                 = "sqlserver-replica-instance-name"  master_instance_name = google_sql_database_instance.primary.name  region               = "europe-west4"  database_version     = "SQLSERVER_2019_ENTERPRISE"  root_password        = "INSERT-PASSWORD-HERE"  replica_configuration {    failover_target = false  }  settings {    tier              = "db-custom-2-7680"    availability_type = "ZONAL"    disk_size         = "100"  }  # set `deletion_protection` to true, will ensure that one cannot accidentally delete this instance by  # use of Terraform whereas `deletion_protection_enabled` flag protects this instance at the GCP level.  deletion_protection = false}

REST v1beta4

Use theinsert method of the instances resource to create the read replica. The region and databaseVersion properties must be the same as the master.

Before using any of the request data, make the following replacements:

project-id: The project ID
database-version: Enum version string (for example, SQLSERVER_2017_ENTERPRISE)
primary-instance-name: The name of the primary instance
primary-instance-region: The region of the primary instance
replica-region: The region of the replica instance
replica-name: The name of the replica instance
machine-type: Enum string of the machine type. For example: "db-custom-1-3840"

You set the value of theipv4Enabled parameter tofalse because you want the Cloud SQL instance to be associated with a private IP address, not a public IP one.

You can use thesqlNetworkArchitecture field to enforce the use of the new networkarchitecture for the instance upon creation, even if the project isn't fully upgraded.For more details about the new network architecture and its implications, see Upgrade an instance to the new network architecture andAllocate an IP address range.

HTTP method and URL:

POST https://sqladmin.googleapis.com/sql/v1beta4/projects/project-id/instances

Request JSON body:

{  "masterInstanceName": "primary-instance-name",  "project": "project-id",  "databaseVersion": "database-version",  "name": "replica-name",  "region": "replica-region",  "settings":  {    "tier": "machine-type",    "settingsVersion": 0,      },  "sqlNetworkArchitecture": "NEW_NETWORK_ARCHITECTURE"}

To send your request, expand one of these options:

curl (Linux, macOS, or Cloud Shell)

Note: The following command assumes that you have logged in to thegcloud CLI with your user account by running gcloud init orgcloud auth login , or by usingCloud Shell, which automatically logs you into thegcloud CLI . You can check the currently active account by runninggcloud auth list.

Save the request body in a file namedrequest.json, and execute the following command:

curl -X POST \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json; charset=utf-8" \
     -d @request.json \
     "https://sqladmin.googleapis.com/sql/v1beta4/projects/project-id/instances"

PowerShell (Windows)

Note: The following command assumes that you have logged in to thegcloud CLI with your user account by running gcloud init orgcloud auth login . You can check the currently active account by runninggcloud auth list.

Save the request body in a file namedrequest.json, and execute the following command:

$cred = gcloud auth print-access-token
$headers = @{ "Authorization" = "Bearer $cred" }

Invoke-WebRequest `
    -Method POST `
    -Headers $headers `
    -ContentType: "application/json; charset=utf-8" `
    -InFile request.json `
    -Uri "https://sqladmin.googleapis.com/sql/v1beta4/projects/project-id/instances" | Select-Object -Expand Content

You should receive a JSON response similar to the following:

Response

{  "kind": "sql#operation",  "targetLink": "https://sqladmin.googleapis.com/sql/v1beta4/projects/project-id/instances/instance-id",  "status": "PENDING",  "user": "user@example.com",  "insertTime": "2020-01-21T22:43:37.981Z",  "operationType": "CREATE_REPLICA",  "name": "operation-id",  "targetId": "instance-id",  "selfLink": "https://sqladmin.googleapis.com/sql/v1beta4/projects/project-id/operations/operation-id",  "targetProject": "project-id"}

Create a read replica of an instance with Private Service Connect enabled

To create a read replica of an instance withPrivate Service Connect enabled, use gcloud CLI or the API. You can create this replica in either the same region or in a different region from the primary instance (cross-region read replica).

The read replica can't replicate from an instance with a different connectivity type. For example, an instance with Private Service Connect enabled can replicate only from another Private Service Connect instance. It also can't replicate from an instance that supports external IP connections or from an instance that's configured withprivate services access.

gcloud

To create a read replica of an instance, use thegcloud sql instances create command:

gcloudsqlinstancescreateREPLICA_INSTANCE_NAME\--master-instance-name=PRIMARY_INSTANCE_NAME\--project=PROJECT_ID\--region=REGION_NAME\--enable-private-service-connect\--allowed-psc-projects=ALLOWED_PROJECTS\--availability-type=AVAILABILITY_TYPE\--no-assign-ip

Make the following replacements:

REPLICA_INSTANCE_NAME: the name of the replica instance.
PRIMARY_INSTANCE_NAME: the name of the primary instance.
PROJECT_ID: the ID orproject number of the Google Cloud project that contains the instance.
REGION_NAME: the region name for the replica instance.
ALLOWED_PROJECTS: a list of allowed project IDs or numbers, separated by commas. If a project isn't contained in this list, then you can't use it to create an instance and enable Private Service Connect for it.
Cloud SQL doesn't copy the allowed projects for the primary instance over to the replica. For each replica, you must create aPrivate Service Connect endpoint. If you're using theCloud SQL Auth Proxy orCloud SQL Language Connectors, then create aDNS zone andDNS record for the replicas.
AVAILABILITY_TYPE: enable high availability for the instance. For this parameter, specify one of the following values:
- REGIONAL: enable high availability and is recommended for production instances. The instance fails over to another zone within your selected region.
- ZONAL: provide no failover capability. This is the default value.
For more information about setting and removing high availability for instances, seeConfigure an existing instance for high availability andDeactivate high availability for an instance.

REST v1

Before using any of the request data, make the following replacements:

PRIMARY_INSTANCE_NAME: the name of the primary instance.
PROJECT_ID: the ID orproject number of the Google Cloud project that contains the instance.
REPLICA_INSTANCE_NAME: the name of the replica instance.
REGION_NAME: the region name for the replica instance.
MACHINE_TYPE: the machine type for the instance.
AVAILABILITY_TYPE: enable high availability for the instance. For this parameter, specify one of the following values:
- REGIONAL: enable high availability and is recommended for production instances. The instance fails over to another zone within your selected region.
- ZONAL: provide no failover capability. This is the default value.
For more information about setting and removing high availability for instances, seeConfigure an existing instance for high availability andDeactivate high availability for an instance.
ALLOWED_PROJECTS: a list of allowed project IDs or numbers, separated by commas. If a project isn't contained in this list, then you can't use it to create an instance and enable Private Service Connect for it.
Cloud SQL doesn't copy the allowed projects for the primary instance over to the replica. For each replica, you must create aPrivate Service Connect endpoint. If you're using theCloud SQL Auth proxy orCloud SQL Language Connectors, then you must create aDNS zone andDNS record for the replicas.

HTTP method and URL:

POST https://sqladmin.googleapis.com/v1/projects/PROJECT_ID/instances

Request JSON body:

{  "masterInstanceName": "PRIMARY_INSTANCE_NAME",  "project": "PROJECT_ID",  "databaseVersion": "SQLSERVER_2019_STANDARD",  "name": "REPLICA_INSTANCE_NAME",  "region": "REGION_NAME",  "kind": "sql#instance",  "settings":  {    "tier": "MACHINE_TYPE",    "availabilityType": "AVAILABILITY_TYPE",    "settingsVersion": 0,    "ipConfiguration": {      "ipv4Enabled": false,      "pscConfig": {        "allowedConsumerProjects": [ALLOWED_PROJECTS],        "pscEnabled": true      }    },    "kind": "sql#settings",    "pricingPlan": "PER_USE",    "replicationType": "ASYNCHRONOUS",    "tier": "MACHINE_TYPE"  }}

To send your request, expand one of these options:

curl (Linux, macOS, or Cloud Shell)

Save the request body in a file namedrequest.json, and execute the following command:

curl -X POST \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json; charset=utf-8" \
     -d @request.json \
     "https://sqladmin.googleapis.com/v1/projects/PROJECT_ID/instances"

PowerShell (Windows)

Save the request body in a file namedrequest.json, and execute the following command:

$cred = gcloud auth print-access-token
$headers = @{ "Authorization" = "Bearer $cred" }

Invoke-WebRequest `
    -Method POST `
    -Headers $headers `
    -ContentType: "application/json; charset=utf-8" `
    -InFile request.json `
    -Uri "https://sqladmin.googleapis.com/v1/projects/PROJECT_ID/instances" | Select-Object -Expand Content

You should receive a JSON response similar to the following:

{  "kind": "sql#operation",  "targetLink": "https://sqladmin.googleapis.com/v1/projects/PROJECT_ID/instances/REPLICA_INSTANCE_NAME",  "status": "PENDING",  "user": "user@example.com",  "insertTime": "2020-01-16T02:32:12.281Z",  "operationType": "CREATE_REPLICA",  "name": "OPERATION_ID",  "targetId": "REPLICA_INSTANCE_NAME",  "selfLink": "https://sqladmin.googleapis.com/v1/projects/PROJECT_ID/operations/OPERATION_ID",  "targetProject": "PROJECT_ID"}

REST v1beta4

Before using any of the request data, make the following replacements:

PRIMARY_INSTANCE_NAME: the name of the primary instance.
PROJECT_ID: the ID orproject number of the Google Cloud project that contains the instance.
REPLICA_INSTANCE_NAME: the name of the replica instance.
REGION_NAME: the region name for the replica instance.
MACHINE_TYPE: the machine type for the instance.
AVAILABILITY_TYPE: enable high availability for the instance. For this parameter, specify one of the following values:
- REGIONAL: enable high availability and is recommended for production instances. The instance fails over to another zone within your selected region.
- ZONAL: provide no failover capability. This is the default value.
For more information about setting and removing high availability for instances, seeConfigure an existing instance for high availability andDeactivate high availability for an instance.
ALLOWED_PROJECTS: a list of allowed project IDs or numbers, separated by commas. If a project isn't contained in this list, then you can't use it to create an instance and enable Private Service Connect for it.
Cloud SQL doesn't copy the allowed projects for the primary instance over to the replica. For each replica, you must create aPrivate Service Connect endpoint. If you're using theCloud SQL Auth proxy orCloud SQL Language Connectors, then you must create aDNS zone andDNS record for the replicas.

HTTP method and URL:

PATCH https://sqladmin.googleapis.com/sql/v1beta4/projects/PROJECT_ID/instances

Request JSON body:

{  "masterInstanceName": "PRIMARY_INSTANCE_NAME",  "project": "PROJECT_ID",  "databaseVersion": "SQLSERVER_2019_STANDARD",  "name": "REPLICA_INSTANCE_NAME",  "region": "REGION_NAME",  "kind": "sql#instance",  "settings":  {    "tier": "MACHINE_TYPE",    "availabilityType": "AVAILABILITY_TYPE",    "settingsVersion": 0,    "ipConfiguration": {      "ipv4Enabled": false,      "pscConfig": {        "allowedConsumerProjects": [ALLOWED_PROJECTS],          "pscEnabled": true      }    },    "kind": "sql#settings",    "pricingPlan": "PER_USE",    "replicationType": "ASYNCHRONOUS",    "tier": "MACHINE_TYPE"  }}

To send your request, expand one of these options:

curl (Linux, macOS, or Cloud Shell)

Save the request body in a file namedrequest.json, and execute the following command:

curl -X PATCH \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json; charset=utf-8" \
     -d @request.json \
     "https://sqladmin.googleapis.com/sql/v1beta4/projects/PROJECT_ID/instances"

PowerShell (Windows)

Save the request body in a file namedrequest.json, and execute the following command:

$cred = gcloud auth print-access-token
$headers = @{ "Authorization" = "Bearer $cred" }

Invoke-WebRequest `
    -Method PATCH `
    -Headers $headers `
    -ContentType: "application/json; charset=utf-8" `
    -InFile request.json `
    -Uri "https://sqladmin.googleapis.com/sql/v1beta4/projects/PROJECT_ID/instances" | Select-Object -Expand Content

You should receive a JSON response similar to the following:

{  "kind": "sql#operation",  "targetLink": "https://sqladmin.googleapis.com/sql/v1beta4/projects/PROJECT_ID/instances/REPLICA_INSTANCE_NAME",  "status": "PENDING",  "user": "user@example.com",  "insertTime": "2020-01-16T02:32:12.281Z",  "operationType": "CREATE_REPLICA",  "name": "OPERATION_ID",  "targetId": "REPLICA_INSTANCE_NAME",  "selfLink": "https://sqladmin.googleapis.com/sql/v1beta4/projects/PROJECT_ID/operations/OPERATION_ID",  "targetProject": "PROJECT_ID"}

Create cascading replicas

This section describes how to create and manage cascading replicas.

For information about how cascading replicas work, seeCascading replicas.

Before you begin

The primary instance must have a cascadable replica. The following section provides the steps to create a cascadable replica.

Steps to create a cascadable replica

When you create a cascadable replica, you must create thereplica in a different region than the primary instance.You configure a cascadable replica by setting thecascadable-replica flag.

gcloud

Create the new replica by specifying the primary instance using the--master-instance-name flag and using the--cascadable-replica flag:

gcloudsqlinstancescreateREPLICA_NAME\--master-instance-name=PRIMARY_INSTANCE_NAME\--cascadable-replica\--region=REGION

Replace the following:

REPLICA_NAME: the unique ID for the replica that you are creating.
PRIMARY_INSTANCE_NAME: the name of the primary instance.
REGION: the region where you want to create the new replica.This region must be different from the region of the primary instance.

You must create the replica in the same VPC network as the primary instance.You can alsospecify an allocated IP range namein that VPC network. If no range is specified, then the replica is created in a random range.

You can add more parameters for other instance settings. For example,

You can specify a different machine tier size using the--tier parameter.
If the primary instance has a private IP address only, then add the--no-assign-ip parameter to the command.

For more information adding parameters for instance settings, seegcloud sql instances create.

After the cascadable replica is created, you can create a cascading replica.

curl

To create a cascadable replica under the primary instance, edit the following JSON code sample, and save it to a file calledrequest.json.
Before using any of the request data, make the following replacements:
- PROJECT_ID: the project ID.
- DATABASE_VERSION: enum string of the database version. For example,SQLSERVER_2017_ENTERPRISE.
- PRIMARY_INSTANCE_NAME: the name of the primary instance.
- PRIMARY_INSTANCE_REGION: the region of the primary instance.
- REPLICA_REGION: the region of the replica instance.
- REPLICA_NAME: the name of the replica instance.
- MACHINE_TYPE: enum string of the machine type. For example,db-custom-2-3840.
```
{"masterInstanceName":"PRIMARY_INSTANCE_NAME","project":"PROJECT_ID","databaseVersion":"DATABASE_VERSION""name":"REPLICA_NAME","region":"REPLICA_REGION","settings":{"tier":"MACHINE_TYPE","settingsVersion":0,}"replicaConfiguration":{"cascadableReplica":true}}
```
In thereplicaConfiguration section, make sure that thecascadadableReplica field is set totrue.

Run the following command:

curl-XPOST-H"Authorization: Bearer "$(gcloudauthprint-access-token)-H"Content-Type: application/json; charset=utf-8"-d@request.json"https://sqladmin.googleapis.com/v1/projects/PROJECT_ID/instances"

After the cascadable replica is created, you can create a cascading replica.

Terraform

To create a cascadable replica, use aTerraform resource.

The following sample creates a primary instance and a cascadable replica that you can assign as the DR replica when you perform aswitchover operation as part ofadvanced disaster recovery (DR).

resource "google_sql_database_instance" "original-primary" {  name   = "sqlserver-primary-instance-name"  region = "us-east1"  # Specify a database version that supports Cloud SQL Enterprise Plus edition.  database_version = "SQLSERVER_2022_ENTERPRISE"  instance_type    = "CLOUD_SQL_INSTANCE"  root_password    = "INSERT-PASSWORD-HERE"  replica_names    = ["sqlserver-replica-instance-name"]  settings {    tier    = "db-perf-optimized-N-2"    edition = "ENTERPRISE_PLUS"    backup_configuration {      enabled = "true"    }  }}resource "google_sql_database_instance" "dr_replica" {  name = "sqlserver-replica-instance-name"  # Specify the original primary instance as the master instance.  master_instance_name = google_sql_database_instance.original-primary.name  # DR replica must be in a different region than the region of the primary instance.  region = "us-west2"  # DR replica must be the same database version as the primary instance.  database_version = "SQLSERVER_2022_ENTERPRISE"  instance_type    = "READ_REPLICA_INSTANCE"  root_password    = "INSERT-PASSWORD-HERE"  replica_configuration {    # Make the replica a cascadable replica.    cascadable_replica = true  }  settings {    # DR replica must be in the same tier as your primary instance and support Enterprise Plus edition.    tier    = "db-perf-optimized-N-2"    edition = "ENTERPRISE_PLUS"  }}

Steps to create a cascading replica

When you create a cascading replica, you must create the replica in thesame region as the cascadable replica. You configure a cascading replicaby providing the name of the cascadable replica inthe–master-instance-name parameter.

Console

In the Google Cloud console, go to theCloud SQL Instances page.
Go to Cloud SQL Instances
Click theReplicas tab for the replica that will act as a parent for the replica that you want to create.
ClickCreate replica.
On theCreate read replica page, update the instance ID, and any other configuration options, including the name, region, and zone.
ClickCreate.
Cloud SQL creates a replica. You're returned to the instance page for the parent replica.
Follow steps 4-6 for each new cascading replica that you want to create.

gcloud

Create the new replica by specifying the cascadable replica instance in the--master-instance-name flag:

gcloudsqlinstancescreateREPLICA_NAME\--master-instance-name=CASCADABLE_REPLICA_NAME\

REPLICA_NAME: the unique ID for the replica that you are creating
CASCADABLE_REPLICA_NAME: the name of the cascadable replica

After you create the cascading replica, you can see that the changesmade to the primary instance are replicated through all the replicas inthe cascading replicas chain.

curl

To create a cascading replica under the cascadable replica, edit the following JSON code sample, and save it to a file calledrequest.json:

{"masterInstanceName":"CASCADABLE_REPLICA_NAME","project":"PROJECT_ID","name":"REPLICA_NAME","region":"REPLICA_REGION","settings":{"tier":"MACHINE_TYPE",}}

Run the following command:

curl-XPOST-H"Authorization: Bearer "$(gcloudauthprint-access-token)-H"Content-Type: application/json; charset=utf-8"-d@request.json"https://sqladmin.googleapis.com/v1/projects/PROJECT_ID/instances"

Troubleshoot

Issue	Troubleshooting
Read replica didn't start replicating on creation.	There's probably a more specific error in the log files.Inspect the logs in Cloud Logging to find the actual error.
Unable to create read replica - invalidFlagValue error.	One of the flags in the request is invalid. It could be a flag you provided explicitly or one that was set to a default value. First, check that the value of the`max_connections` flag is greater than or equal to the value on the primary. If the`max_connections` flag is set appropriately,inspect the logs in Cloud Logging to find the actual error.
Unable to create read replica - unknown error.	There's probably a more specific error in the log files.Inspect the logs in Cloud Logging to find the actual error. If the error is:`set Service Networking service account as servicenetworking.serviceAgent role on consumer project`, then disable and re-enable the`Service Networking API`. This action creates the service account necessary to continue with the process.
Disk is full.	The primary instance disk size can become full during replica creation. Edit the primary instance to upgrade it to a larger disk size.
The replica instance is using too much memory.	The replica uses temporary memory to cache often-requested read operations, which can lead it to use more memory than the primary instance. Restart the replica instance to reclaim the temporary memory space.
Replication stopped.	The maximum storage limit was reached and automatic storage increase isn't enabled. Edit the instance to enable`automatic storage increase`.
Replication lag is consistently high.	The write load is too high for the replica to handle. Replication lag takes place when the SQL thread on a replica is unable to keep up with the IO thread. Some kinds of queries or workloads can cause temporary or permanent high replication lag for a given schema. Some of the typical causes of replication lag are: Slow queries on the replica. Find and fix them. Queries like`DELETE ... WHERE field < 50000000` cause replication lag with row-based replication since a huge number of updates are piled up on the replica. Some possible solutions include: Edit the instance to increase the size of the replica. Reduce the load on the database. Send read traffic to the read replica. Index the tables. Identify and fix slow write queries. Recreate the replica.
Replica creation fails with timeout.	Long-running uncommitted transactions on the primary instance can cause read replica creation to fail. Recreate the replica after stopping all running queries.

What's next

Learn how tomanage replicas.
Learn aboutcross-region replicas.
Learn aboutAdvanced disaster recovery (DR)

Except as otherwise noted, the content of this page is licensed under theCreative Commons Attribution 4.0 License, and code samples are licensed under theApache 2.0 License. For details, see theGoogle Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.

Last updated 2025-12-17 UTC.

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Create read replicas Stay organized with collections Save and categorize content based on your preferences.

Before you begin

Create a read replica

Console

gcloud

Terraform

REST v1beta4

curl (Linux, macOS, or Cloud Shell)

PowerShell (Windows)

Response

Create a read replica of an instance with Private Service Connect enabled

gcloud

REST v1

curl (Linux, macOS, or Cloud Shell)

PowerShell (Windows)

REST v1beta4

curl (Linux, macOS, or Cloud Shell)

PowerShell (Windows)

Create cascading replicas

Before you begin

Steps to create a cascadable replica

gcloud

curl

Terraform

Steps to create a cascading replica

Console

gcloud

curl

Troubleshoot

What's next

Create read replicas