AWS recently announced the general availability of RDS Blue/Green Deployments, a new feature for RDS and Aurora to perform blue/green database updates. One of the aspects that caught my eye is how fast a switchover is.
In as fast as a minute, you can promote the staging environment to be the new production environment with no data loss.Channy Yun, principal developer advocate at AWS
Let’s give it a try! How can we check how long a switchover really takes? We will perform the simplest test, using only a MySQL client and a while loop in Bash:
while true; do mysql -s -N -h renato-cluster.***.eu-west-1.rds.amazonaws.com -u renato -e "select now()"; sleep 1; done (...) 2022-12-09 07:58:55 2022-12-09 07:58:56 2022-12-09 07:58:57 2022-12-09 07:58:58 (...)
We keep asking every second for the current date and time to the RDS server and we will check what happens when we trigger a switchover. We will compare the results with a reboot and a reboot with failover. To perform the test we will use an m6g.large Multi-AZ instance with some production traffic, a cluster where the Seconds_Behind_Master value of a replica hardly goes above a single-digit number.
Rebooting an instance
Using the CLI, we can perform a reboot of an RDS instance without forcing a failover of the database server.
aws rds reboot-db-instance --db-instance-identifier renato-cluster --no-force-failover (...) 2022-12-09 08:00:01 2022-12-09 08:00:02 2022-12-09 08:00:03 2022-12-09 08:00:23 2022-12-09 08:00:24 2022-12-09 08:00:25 (...)
That is just about 20 seconds for a reboot of an RDS instance.
Rebooting with failover
We can now repeat the test forcing a failover:
aws rds reboot-db-instance --db-instance-identifier renato-cluster --force-failover (...) 2022-12-09 08:01:11 2022-12-09 08:01:12 2022-12-09 08:01:13 2022-12-09 08:03:28 2022-12-09 08:03:29 2022-12-09 08:03:30 (...)
This time it takes longer, including the time required to switch the CNAME of our database to the new IP address: 2 minutes and 15 seconds.
Switching a blue/green deployment
Finally, we can trigger a switchover in our blue/green deployment calling:
aws rds switchover-blue-green-deployment --blue-green-deployment-identifier renato-cluster-bg (...) 2022-12-09 08:06:59 2022-12-09 08:07:00 2022-12-09 08:07:01 2022-12-09 08:08:07 2022-12-09 08:08:08 2022-12-09 08:08:09 (...)
The switchover time of the RDS Blue/Green Deployments is just about a minute: 1 minute and 6 seconds.
- Reboot: 20 seconds
- Reboot with failover: 135 seconds
- Switchover: 66 seconds
The switchover of an RDS for MySQL instance is “as fast as a minute” and significantly faster than a reboot with failover of a Multi-AZ instance. Of course, the switchover can take significantly longer according to the write load of your production database. This was only a basic test to validate the minimum downtime for a switchover.
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