From ed035e83f9c5509a1167dc2da96d09a3b4dcdb47 Mon Sep 17 00:00:00 2001 From: Michele Cereda Date: Wed, 1 Oct 2025 10:04:51 +0200 Subject: [PATCH] chore(kb/aws/rds): revise multi-az section --- knowledge base/cloud computing/aws/rds.md | 43 ++++++++++++++++++----- 1 file changed, 34 insertions(+), 9 deletions(-) diff --git a/knowledge base/cloud computing/aws/rds.md b/knowledge base/cloud computing/aws/rds.md index dfe4fa7..84cd254 100644 --- a/knowledge base/cloud computing/aws/rds.md +++ b/knowledge base/cloud computing/aws/rds.md @@ -15,6 +15,7 @@ 1. [Export snapshots to S3](#export-snapshots-to-s3) 1. [Restore](#restore) 1. [Multi-AZ instances](#multi-az-instances) + 1. [Converting instances between Multi-AZ and Single-AZ](#converting-instances-between-multi-az-and-single-az) 1. [Operations](#operations) 1. [PostgreSQL: reduce allocated storage by migrating using transportable databases](#postgresql-reduce-allocated-storage-by-migrating-using-transportable-databases) 1. [Stop instances](#stop-instances) @@ -529,14 +530,9 @@ Refer the [Backup] section for what this means. ## Multi-AZ instances -Refer [Multi-AZ DB instance deployments for Amazon RDS] and -[When modifying a Multi-AZ RDS to Single Instance the AZ was changed!!]. +Refer [Multi-AZ DB instance deployments for Amazon RDS]. -RDS DB instances can be configured for high availability and failover support by using Multi-AZ deployments. - -RDS uses several different technologies to provide failover support. It supports MariaDB, MySQL, Oracle, PostgreSQL, -and RDS Custom for SQL Server DB instances.
-Microsoft SQL Server DB instances use SQL Server Database Mirroring or Always On Availability Groups. +DB instances can be configured for high availability and failover support by using Multi-AZ deployments. RDS provisions and maintains a synchronous standby replica in a different AZ, which continuously syncs with the primary DB instance.
@@ -550,6 +546,13 @@ system maintenance, and helps protect the database against DB instance failure a Multi-AZ DB instance deployments have increased costs, and write and commit latency compared to Single-AZ deployments due to the synchronous data replication to the standby replica. +A Single-AZ configuration deploys a DB instance and its EBS storage volumes in one AZ.
+A Multi-AZ configuration deploys a DB instance and its EBS storage volumes across two or more AZs. + +RDS uses several different technologies to provide failover support. It supports MariaDB, MySQL, Oracle, PostgreSQL, +and RDS Custom for SQL Server DB instances.
+Microsoft SQL Server DB instances use SQL Server Database Mirroring or Always On Availability Groups. + If an infrastructure defect results in any outage of a Multi-AZ DB instance, RDS automatically switches to the standby replica.
The failover typically takes 60 to 120 seconds, but it depends on the database activity and other conditions at the time @@ -557,6 +560,25 @@ the primary DB instance became unavailable. Large transactions or a lengthy reco time.
When the failover is complete, it can take additional time for the RDS console to reflect the new AZ. +For a Multi-AZ deployment, RDS creates DB snapshots and automated backups **from the secondary instance** during the +automatic backup window. This prevents the backup process from suspending I/O activity on the primary instance on all +engines but SQL Server.
+In a Single-AZ deployment, the backup process does result in a brief I/O suspension that can last from a few seconds to +a few minutes. The amount of time depends on the size and class of the DB instance. + +A Single-AZ instance is unavailable during a scaling operation.
+For Multi-AZ deployments, RDS achieves minimal downtime during certain OS patches or scaling operations by: + +1. Applying OS maintenance and scaling operations to the secondary instance first. +1. Promoting the secondary instance to primary, and demoting the old primary instance to secondary. +1. Performing maintenance or modifications on the old primary, now secondary instance. + +### Converting instances between Multi-AZ and Single-AZ + +Refer +[What happens when I change my RDS DB instance from a Single-AZ to a Multi-AZ deployment or a Multi-AZ to a Single-AZ deployment?] +and [When modifying a Multi-AZ RDS to Single Instance the AZ was changed!!]. + One can convert existing Single-AZ DB instances to Multi-AZ deployments just by modifying the DB instance.
This process involves minimal to no downtime, but requires planning around storage and performance impacts if done on active instances. @@ -564,14 +586,16 @@ active instances. During a Single-AZ to Multi-AZ conversion, RDS: 1. Takes a snapshot of the primary DB instance's EBS volumes. -1. Creates new volumes for the standby replica from that snapshot. +1. Creates new volumes for the standby replica from that snapshot in another AZ. 1. Turns on synchronous block-level replication between the volumes of the primary and standby replicas. +1. Creates the new standby replica instance in the AZ where the volumes were created, and attaches them to it. One can convert existing Multi-AZ DB instances to Single-AZ deployments just by modifying the DB instance.
This process involves minimal to no downtime, but requires planning around storage and performance impacts if done on active instances. -During a Multi-AZ to Single-AZ conversion, RDS typically keeps the instance in the AZ where the primary was located. +During a Multi-AZ to Single-AZ conversion, RDS typically keeps the instance in the AZ where the primary was located and +deletes only the secondary instance and volumes. The change does **not** typically affect the primary instance. ## Operations @@ -1037,6 +1061,7 @@ or write workloads and exceeds the instance type quotas. [transporting postgresql databases between db instances]: https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/PostgreSQL.TransportableDB.html [understanding postgresql roles and permissions]: https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Appendix.PostgreSQL.CommonDBATasks.Roles.html [viewing instance status]: https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/accessing-monitoring.html +[What happens when I change my RDS DB instance from a Single-AZ to a Multi-AZ deployment or a Multi-AZ to a Single-AZ deployment?]: https://repost.aws/knowledge-center/rds-convert-single-az-multi-az [what is aws database migration service?]: https://docs.aws.amazon.com/dms/latest/userguide/Welcome.html [When modifying a Multi-AZ RDS to Single Instance the AZ was changed!!]: https://repost.aws/questions/QUmpYrb5etT0-de8woCv4rYQ/when-modifying-a-multi-az-rds-to-single-instance-the-az-was-changed [Why is my Amazon RDS DB instance in the storage-optimization state for a long time?]: https://repost.aws/knowledge-center/rds-stuck-in-storage-optimization