Zonal shift in Amazon Route 53 Application Recovery Controller - Amazon Route 53 Application Recovery Controller

Zonal shift in Amazon Route 53 Application Recovery Controller

With zonal shift in Amazon Route 53 Application Recovery Controller, you can move traffic for an Elastic Load Balancing resource away from an Availability Zone in an AWS Region, to quickly mitigate an issue and quickly recover your application. Note that the Elastic Load Balancing resources must have cross-zone load balancing turned off to use this capability.

When you deploy and run AWS applications on load balancers in multiple (typically three) AZs in a Region, you can quickly recover an application in an impaired AZ by starting a zonal shift. Shifting your application traffic to healthy AZs reduces the duration and severity of impact caused by power outages, or hardware or software issues in an AZ.

You might choose to shift traffic, for example, because a bad deployment is causing latency issues, or because the Availability Zone is impaired. A zonal shift requires no advance configuration steps, but your AWS configuration must support handling your client load without the Availability Zone that you shift away from. Supported load balancer resources are automatically registered with Amazon Route 53 Application Recovery Controller for you, so that you can simply start a zonal shift for the load balancer when needed.

Starting a zonal shift requires no setup or configuration. After you ensure that you have sufficient capacity to shift traffic away from an Availability Zone, choose the Availability Zone to shift away from and the resource to shift traffic away for, and then start the zonal shift. You can cancel the shift at any time, to have traffic begin returning to the Availability Zone.

All zonal shifts are temporary mitigations. You set an initial expiration when you start a zonal shift, from one hour up to three days (72 hours), which you can extend, if you need to continue the traffic shift.

Be aware that, in a few specific scenarios, zonal shift does not shift traffic from the AZ. For more information about zonal shift support, see Resources supported for zonal shift and zonal autoshift.

Ensuring that traffic shifts finish quickly

When you perform a zonal shift away from an Availability Zone, or use routing controls to shift from one AWS Region to another, the mechanism that Amazon Route 53 Application Recovery Controller uses to move your application traffic is a DNS update. This update causes all new connections to be directed away from the impaired location.

However, clients with pre-existing open connections might continue to make requests against the impaired location until they reconnect. To ensure a quick recovery, we recommend that you limit the amount of time clients stay connected to your endpoints.

If you use an Application Load Balancer, you can use its HTTP client keepalive duration option to configure how long connections continue. For more information, see HTTP client keepalive duration in the Application Load Balancer User Guide.

By default, Application Load Balancers set the HTTP client keepalive duration value to 3600 seconds, or 1 hour. We suggest that you lower the value to be inline with your recovery time goal for your application, for example, 300 seconds. When you choose an HTTP client keepalive duration time, consider that this value is a trade off between reconnecting more frequently in general, which can affect latency, and more quickly moving all clients away from an impaired AZ or Region.