Managing a Multi-AZ deployment for RDS Custom for SQL Server - Amazon Relational Database Service
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Managing a Multi-AZ deployment for RDS Custom for SQL Server

In a Multi-AZ DB instance deployment for RDS Custom for SQL Server, Amazon RDS automatically provisions and maintains a synchronous standby replica in a different Availability Zone (AZ). The primary DB instance is synchronously replicated across Availability Zones to a standby replica to provide data redundancy.

Important

A Multi-AZ deployment for RDS Custom for SQL Server is different than Multi-AZ for RDS for SQL Server. Unlike Multi-AZ for RDS for SQL Server, you must set up prerequisites for RDS Custom for SQL Server before creating your Multi-AZ DB instance because RDS Custom runs inside your own account, which requires permissions.

If you don't complete the prerequisites, your Multi-AZ DB instance might fail to run, or automatically revert to a Single-AZ DB instance. For more information about prerequisites, see Prerequisites for a Multi-AZ deployment with RDS Custom for SQL Server.

Running a DB instance with high availability can enhance availability during planned system maintenance. In the event of planned database maintenance or unplanned service disruption, Amazon RDS automatically fails over to the up-to-date secondary DB instance. This functionality lets database operations resume quickly without manual intervention. The primary and standby instances use the same endpoint, whose physical network address transitions to the secondary replica as part of the failover process. You don't have to reconfigure your application when a failover occurs.

RDS Custom for SQL Server supports Multi-AZ.

You can create an RDS Custom for SQL Server Multi-AZ deployment by specifying Multi-AZ when creating an RDS Custom DB instance. You can use the console to convert existing RDS Custom for SQL Server DB instances to Multi-AZ deployments by modifying the DB instance and specifying the Multi-AZ option. You can also specify a Multi-AZ DB instance deployment with the Amazon CLI or Amazon RDS API.

The RDS console shows the Availability Zone of the standby replica (the secondary AZ). You can also use the describe-db-instances CLI command or the DescribeDBInstances API operation to find the secondary AZ.

RDS Custom for SQL Server DB instances with Multi-AZ deployment can have increased write and commit latency compared to a Single-AZ deployment. This increase can happen because of the synchronous data replication between DB instances. You might have a change in latency if your deployment fails over to the standby replica, although Amazon is engineered with low-latency network connectivity between Availability Zones.

Note

For production workloads, we recommend that you use a DB instance class with Provisioned IOPS (input/output operations per second) for fast, consistent performance. For more information about DB instance classes, see Requirements and limitations for Amazon RDS Custom for SQL Server.

Region and version availability

Multi-AZ deployments for RDS Custom for SQL Server are supported for the following SQL Server editions:

  • SQL Server 2022 and 2019: Enterprise, Standard, Web, and Developer Edition

Note

Multi-AZ deployments for RDS Custom for SQL Server aren't supported on SQL Server 2019 CU8 (15.00.4073.23) or lower versions.

Multi-AZ deployments for RDS Custom for SQL Server are available in all Regions where RDS Custom for SQL Server is available. For more information on Region availability of Multi-AZ deployments for RDS Custom for SQL Server, see Supported Regions and DB engines for RDS Custom for SQL Server.

Limitations for a Multi-AZ deployment with RDS Custom for SQL Server

Multi-AZ deployments with RDS Custom for SQL Server have the following limitations:

  • Cross-Region Multi-AZ deployments aren't supported.

  • You can’t configure the secondary DB instance to accept database read activity.

  • When you use a Custom Engine Version (CEV) with a Multi-AZ deployment, your secondary DB instance will also use the same CEV. The secondary DB instance can't use a different CEV.

Prerequisites for a Multi-AZ deployment with RDS Custom for SQL Server

If you have an existing RDS Custom for SQL Server Single-AZ deployment, the following additional prerequisites are required before modifying it to a Multi-AZ deployment. You can choose to complete the prerequisites manually or with the provided CloudFormation template. The latest CloudFormation template contains the prerequisites for both Single-AZ and Multi-AZ deployments.

Important

To simplify setup, we recommend that you use the latest Amazon CloudFormation template file provided in the network setup instructions to create the prerequisites. For more information, see Configuring with Amazon CloudFormation.

Note

When you modify an existing RDS Custom for SQL Server Single-AZ deployment to a Multi-AZ deployment, you must complete these prerequisites. If you don't complete the prerequisites, the Multi-AZ setup will fail. To complete the prerequisites, follow the steps in Modifying an RDS Custom for SQL Server Single-AZ deployment to a Multi-AZ deployment.

  • Update the RDS security group inbound and outbound rules to allow port 1120.

  • Add a rule in your private network Access Control List (ACL) that allows TCP ports 0-65535 for the DB instance VPC.

  • Create new Amazon SQS VPC endpoints that allow the RDS Custom for SQL Server DB instance to communicate with SQS.

  • Update the SQS permissions in the instance profile role.

Creating an RDS Custom for SQL Server Multi-AZ deployment

To create an RDS Custom for SQL Server Multi-AZ deployment, follow the steps in Creating and connecting to a DB instance for Amazon RDS Custom for SQL Server.

Important

To simplify setup, we recommend that you use the latest Amazon CloudFormation template file provided in the network setup instructions. For more information, see Configuring with Amazon CloudFormation.

Creating a Multi-AZ deployment takes a few minutes to complete.

Modifying an RDS Custom for SQL Server Single-AZ deployment to a Multi-AZ deployment

You can modify an existing RDS Custom for SQL Server DB instance from a Single-AZ deployment to a Multi-AZ deployment. When you modify the DB instance,Amazon RDS performs several actions:

  • Takes a snapshot of the primary DB instance.

  • Creates new volumes for the standby replica from the snapshot. These volumes initialize in the background, and maximum volume performance is achieved after the data is fully initialized.

  • Turns on synchronous block-level replication between the primary and secondary DB instances.

Important

We recommend that you avoid modifying your RDS Custom for SQL Server DB instance from a Single-AZ to a Multi-AZ deployment on a production DB instance during periods of peak activity.

Amazon uses a snapshot to create the standby instance to avoid downtime when you convert from Single-AZ to Multi-AZ, but performance might be impacted during and after converting to Multi-AZ. This impact can be significant for workloads that are sensitive to write latency. While this capability allows large volumes to quickly be restored from snapshots, it can cause increase in the latency of I/O operations because of the synchronous replication. This latency can impact your database performance.

Configuring prerequisites to modify a Single-AZ to a Multi-AZ deployment using CloudFormation

To use a Multi-AZ deployment, you must ensure you've applied the latest CloudFormation template with prerequisites, or manually configure the latest prerequisites. If you've already applied the latest CloudFormation prerequisite template, you can skip these steps.

To configure the RDS Custom for SQL Server Multi-AZ deployment prerequisites using CloudFormation

  1. Open the CloudFormation console at https://console.amazonaws.cn/cloudformation.

  2. To start the Create Stack wizard, select the existing stack you used to create a Single-AZ deployment and choose Update.

    The Update stack page appears.

  3. For Prerequisite - Prepare template, choose Replace current template.

  4. For Specify template, do the following:

    1. Download the latest Amazon CloudFormation template file. Open the context (right-click) menu for the link custom-sqlserver-onboard.zip and choose Save Link As.

    2. Save and extract the custom-sqlserver-onboard.json file to your computer.

    3. For Template source, choose Upload a template file.

    4. For Choose file, navigate to and then choose custom-sqlserver-onboard.json.

  5. Choose Next.

    The Specify stack details page appears.

  6. To keep the default options, choose Next.

    The Advanced Options page appears.

  7. To keep the default options, choose Next.

  8. To keep the default options, choose Next.

  9. On the Review Changes page, do the following:

    1. For Capabilities, select the I acknowledge that Amazon CloudFormation might create IAM resources with custom names check box.

    2. Choose Submit.

  10. Verify the update is successful. The status of a successful operation shows UPDATE_COMPLETE.

If the update fails, any new configuration specified in the update process will be rolled back. The existing resource will still be usable. For example, if you add network ACL rules numbered 18 and 19, but there were existing rules with same numbers, the update would return the following error: Resource handler returned message: "The network acl entry identified by 18 already exists. In this scenario you can modify the existing ACL rules to use a number lower than 18, then retry the update.

Configuring prerequisites to modify a Single-AZ to a Multi-AZ deployment manually

Important

To simplify setup, we recommend that you use the latest Amazon CloudFormation template file provided in the network setup instructions. For more information, see Configuring prerequisites to modify a Single-AZ to a Multi-AZ deployment using CloudFormation.

If you choose to configure the prerequisites manually, perform the following tasks.

  1. Open the Amazon VPC console at https://console.amazonaws.cn/vpc/.

  2. Choose Endpoint. The Create Endpoint page appears.

  3. For Service Category, choose Amazon services.

  4. In Services, search for SQS

  5. In VPC, choose the VPC where your RDS Custom for SQL Server DB instance is deployed.

  6. In Subnets, choose the subnets where your RDS Custom for SQL Server DB instance is deployed.

  7. In Security Groups, choose the -vpc-endpoint-sg group.

  8. For Policy, choose Custom

  9. In your custom policy, replace the Amazon partition, Region, accountId,and IAM-Instance-role with your own values.

    { "Version": "2012-10-17", "Statement": [ { "Condition": { "StringLike": { "aws:ResourceTag/AWSRDSCustom": "custom-sqlserver" } }, "Action": [ "SQS:SendMessage", "SQS:ReceiveMessage", "SQS:DeleteMessage", "SQS:GetQueueUrl" ], "Resource": "arn:${AWS::Partition}:sqs:${AWS::Region}:${AWS::AccountId}:do-not-delete-rds-custom-*", "Effect": "Allow", "Principal": { "AWS": "arn:${AWS::Partition}:iam::${AWS::AccountId}:role/{IAM-Instance-role}" } } ] }
  10. Update the Instance profile with permission to access Amazon SQS. Replace the Amazon partition, Region, and accountId with your own values.

    { "Sid": "SendMessageToSQSQueue", "Effect": "Allow", "Action": [ "SQS:SendMessage", "SQS:ReceiveMessage", "SQS:DeleteMessage", "SQS:GetQueueUrl" ], "Resource": [ { "Fn::Sub": "arn:${AWS::Partition}:sqs:${AWS::Region}:${AWS::AccountId}:do-not-delete-rds-custom-*" } ], "Condition": { "StringLike": { "aws:ResourceTag/AWSRDSCustom": "custom-sqlserver" } } } >
  11. Update the Amazon RDS security group inbound and outbound rules to allow port 1120.

    1. In Security Groups, choose the -rds-custom-instance-sg group.

    2. For Inbound Rules, create a Custom TCP rule to allow port 1120 from the source -rds-custom-instance-sg group.

    3. For Outbound Rules, create a Custom TCP rule to allow port 1120 to the destination -rds-custom-instance-sg group.

  12. Add a rule in your private network Access Control List (ACL) that allows TCP ports 0-65535 for the source subnet of the DB instance.

    Note

    When creating an Inbound Rule and Outbound Rule, take note of the highest existing Rule number. The new rules you create must have a Rule number lower than 100 and not match any existing Rule number.

    1. In Network ACLs, choose the -private-network-acl group.

    2. For Inbound Rules, create an All TCP rule to allow TCP ports 0-65535 with a source from privatesubnet1 and privatesubnet2.

    3. For Outbound Rules, create an All TCP rule to allow TCP ports 0-65535 to destination privatesubnet1 and privatesubnet2.

Modify using the RDS console, Amazon CLI, or RDS API.

After you've completed the prerequisites, you can modify an RDS Custom for SQL Server DB instance from a Single-AZ to Multi-AZ deployment using the RDS console, Amazon CLI, or RDS API.

To modify an existing RDS Custom for SQL Server Single-AZ to Multi-AZ deployment
  1. Sign in to the Amazon Web Services Management Console and open the Amazon RDS console at https://console.amazonaws.cn/rds/.

  2. In the Amazon RDS console, choose Databases.

    The Databases pane appears.

  3. Choose the RDS Custom for SQL Server DB instance that you want to modify.

  4. For Actions, choose Convert to Multi-AZ deployment.

  5. On the Confirmation page, choose Apply immediately to apply the changes immediately. Choosing this option doesn't cause downtime, but there is a possible performance impact. Alternatively, you can choose to apply the update during the next maintenance window. For more information, see Schedule modifications setting.

  6. On the Confirmation page, choose Convert to Multi-AZ.

To convert to a Multi-AZ DB instance deployment by using the Amazon CLI, call the modify-db-instance command and set the --multi-az option. Specify the DB instance identifier and the values for other options that you want to modify. For information about each option, see Settings for DB instances.

Example

The following code modifies mycustomdbinstance by including the --multi-az option. The changes are applied during the next maintenance window by using --no-apply-immediately. Use --apply-immediately to apply the changes immediately. For more information, see Schedule modifications setting.

For Linux, macOS, or Unix:

aws rds modify-db-instance \ --db-instance-identifier mycustomdbinstance \ --multi-az \ --no-apply-immediately

For Windows:

aws rds modify-db-instance ^ --db-instance-identifier mycustomdbinstance ^ --multi-az \ ^ --no-apply-immediately

To convert to a Multi-AZ DB instance deployment with the RDS API, call the ModifyDBInstance operation and set the MultiAZ parameter to true.

Modifying an RDS Custom for SQL Server Multi-AZ deployment to a Single-AZ deployment

You can modify an existing RDS Custom for SQL Server DB instance from a Multi-AZ to a Single-AZ deployment.

To modify an RDS Custom for SQL Server DB instance from a Multi-AZ to Single-AZ deployment.
  1. Sign in to the Amazon Web Services Management Console and open the Amazon RDS console at https://console.amazonaws.cn/rds/.

  2. In the Amazon RDS console, choose Databases.

    The Databases pane appears.

  3. Choose the RDS Custom for SQL Server DB instance that you want to modify.

  4. For Multi-AZ deployment, choose No.

  5. On the Confirmation page, choose Apply immediately to apply the changes immediately. Choosing this option doesn't cause downtime, but there is a possible performance impact. Alternatively, you can choose to apply the update during the next maintenance window. For more information, see Schedule modifications setting.

  6. On the Confirmation page, choose Modify DB Instance.

To modify a Multi-AZ deployment to a Single-AZ deployment by using the Amazon CLI, call the modify-db-instance command and include the --no-multi-az option. Specify the DB instance identifier and the values for other options that you want to modify. For information about each option, see Settings for DB instances.

Example

The following code modifies mycustomdbinstance by including the --no-multi-az option. The changes are applied during the next maintenance window by using --no-apply-immediately. Use --apply-immediately to apply the changes immediately. For more information, see Schedule modifications setting.

For Linux, macOS, or Unix:

aws rds modify-db-instance \ --db-instance-identifier mycustomdbinstance \ --no-multi-az \ --no-apply-immediately

For Windows:

aws rds modify-db-instance ^ --db-instance-identifier mycustomdbinstance ^ --no-multi-az \ ^ --no-apply-immediately

To modify a Multi-AZ deployment to a Single-AZ deployment by using the RDS API, call the ModifyDBInstance operation and set the MultiAZ parameter to false.

Failover process for an RDS Custom for SQL Server Multi-AZ deployment

If a planned or unplanned outage of your DB instance results from an infrastructure defect, Amazon RDS automatically switches to a standby replica in another Availability Zone if you have turned on Multi-AZ. The time that it takes for the failover to complete depends on the database activity and other conditions at the time that the primary DB instance became unavailable. Failover times are typically 60 – 120 seconds. However, large transactions or a lengthy recovery process can increase failover time. When the failover is complete, it can take additional time for the RDS console to show the new Availability Zone.

Note

You can force a failover manually when you reboot a DB instance with failover. For more information on rebooting a DB instance, see Rebooting a DB instance

Amazon RDS handles failovers automatically so you can resume database operations as quickly as possible without administrative intervention. The primary DB instance switches over automatically to the standby replica if any of the conditions described in the following table occurs. You can view these failover reasons in the RDS event log.

Failover reason Description

The operating system for the RDS Custom for SQL Server Multi-AZ DB instance is being patched in an offline operation

A failover was triggered during the maintenance window for an OS patch or a security update. For more information, see Maintaining a DB instance.

The primary host of the RDS Custom for SQL Server Multi-AZ DB instance is unhealthy.

The Multi-AZ DB instance deployment detected an impaired primary DB instance and failed over.

The primary host of the RDS Custom for SQL Server Multi-AZ DB instance is unreachable due to loss of network connectivity.

RDS monitoring detected a network reachability failure to the primary DB instance and triggered a failover.

The RDS Custom for SQL Server Multi-AZ DB instance was modified by the customer.

A DB instance modification triggered a failover. For more information, see Modifying an RDS Custom for SQL Server DB instance.

The storage volume of the primary host of the RDS Custom for SQL Server Multi-AZ DB instance experienced a failure.

The Multi-AZ DB instance deployment detected a storage issue on the primary DB instance and failed over.

The user requested a failover of the RDS Custom for SQL Server Multi-AZ DB instance.

The RDS Custom for SQL Server Multi-AZ DB instance was rebooted with failover. For more information, see Rebooting a DB instance.

The RDS Custom for SQL Server Multi-AZ primary DB instance is busy or unresponsive.

The primary DB instance is unresponsive. We recommend that you try the following steps:

To determine if your Multi-AZ DB instance has failed over, you can do the following:

  • Set up DB event subscriptions to notify you by email or SMS that a failover has been initiated. For more information about events, see Working with Amazon RDS event notification.

  • View your DB events by using the RDS console or API operations.

  • View the current state of your RDS Custom for SQL Server Multi-AZ DB instance deployment by using the RDS console, CLI, or API operations.

Time to live (TTL) settings with applications using an RDS Custom for SQL Server Multi-AZ deployment

The failover mechanism automatically changes the Domain Name System (DNS) record of the DB instance to point to the standby DB instance. As a result, you need to re-establish any existing connections to your DB instance. Ensure that any DNS cache time-to-live (TTL) configuration value is low, and validate that your application will not cache DNS for an extended time. A high TTL value might prevent your application from quickly reconnecting to the DB instance after failover.