REL11-BP04 Rely on the data plane and not the control plane during recovery - AWS Well-Architected Framework
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REL11-BP04 Rely on the data plane and not the control plane during recovery

Control planes provide the administrative APIs used to create, read and describe, update, delete, and list (CRUDL) resources, while data planes handle day-to-day service traffic. When implementing recovery or mitigation responses to potentially resiliency-impacting events, focus on using a minimal number of control plane operations to recover, rescale, restore, heal, or failover the service. Data plane action should supersede any activity during these degradation events.

For example, the following are all control plane actions: launching a new compute instance, creating block storage, and describing queue services. When you launch compute instances, the control plane has to perform multiple tasks like finding a physical host with capacity, allocating network interfaces, preparing local block storage volumes, generating credentials, and adding security rules. Control planes tend to be complicated orchestration.

Desired outcome: When a resource enters an impaired state, the system is capable of automatically or manually recovering by shifting traffic from impaired to healthy resources.

Common anti-patterns:

  • Dependence on changing DNS records to re-route traffic.

  • Dependence on control-plane scaling operations to replace impaired components due to insufficiently provisioned resources.

  • Relying on extensive, multi service, multi-API control plane actions to remediate any category of impairment.

Benefits of establishing this best practice: Increased success rate for automated remediation can reduce your mean time to recovery and improve availability of the workload.

Level of risk exposed if this best practice is not established: Medium: For certain types of service degradations, control planes are affected. Dependencies on extensive use of the control plane for remediation may increase recovery time (RTO) and mean time to recovery (MTTR).

Implementation guidance

To limit data plane actions, assess each service for what actions are required to restore service.

Leverage Amazon Route 53 Application Recovery Controller to shift the DNS traffic. These features continually monitor your application’s ability to recover from failures and allow you to control your application recovery across multiple AWS Regions, Availability Zones, and on premises.

Route 53 routing policies use the control plane, so do not rely on it for recovery. The Route 53 data planes answer DNS queries and perform and evaluate health checks. They are globally distributed and designed for a 100% availability service level agreement (SLA).

The Route 53 management APIs and consoles where you create, update, and delete Route 53 resources run on control planes that are designed to prioritize the strong consistency and durability that you need when managing DNS. To achieve this, the control planes are located in a single Region: US East (N. Virginia). While both systems are built to be very reliable, the control planes are not included in the SLA. There could be rare events in which the data plane’s resilient design allows it to maintain availability while the control planes do not. For disaster recovery and failover mechanisms, use data plane functions to provide the best possible reliability.

For Amazon EC2, use static stability designs to limit control plane actions. Control plane actions include the scaling up of resources individually or using Auto Scaling groups (ASG). For the highest levels of resilience, provision sufficient capacity in the cluster used for failover. If this capacity threshold must be limited, set throttles on the overall end-to-end system to safely limit the total traffic reaching the limited set of resources.

For services like Amazon DynamoDB, Amazon API Gateway, load balancers, and AWS Lambda serverless, using those services leverages the data plane. However, creating new functions, load balancers, API gateways, or DynamoDB tables is a control plane action and should be completed before the degradation as preparation for an event and rehearsal of failover actions. For Amazon RDS, data plane actions allow for access to data.

For more information about data planes, control planes, and how AWS builds services to meet high availability targets, see Static stability using Availability Zones.

Understand which operations are on the data plane and which are on the control plane.

Implementation steps

For each workload that needs to be restored after a degradation event, evaluate the failover runbook, high availability design, auto healing design, or HA resource restoration plan. Identity each action that might be considered a control plane action.

Consider changing the control action to a data plane action:

  • Auto Scaling (control plane) compared to pre-scaled Amazon EC2 resources (data plane)

  • Migrate to Lambda and its scaling methods (data plane) or Amazon EC2 and ASG (control plane)

  • Assess any designs using Kubernetes and the nature of the control plane actions. Adding pods is a data plane action in Kubernetes. Actions should be limited to adding pods and not adding nodes. Using over-provisioned nodes is the preferred method to limit control plane actions

Consider alternate approaches that allow for data plane actions to affect the same remediation.

Consider some services in a secondary Region, if the service is mission critical, to allow for more control plane and data plane actions in an unaffected Region.

  • Amazon EC2 Auto Scaling or Amazon EKS in a primary Region compared to Amazon EC2 Auto Scaling or Amazon EKS in a secondary Region and routing traffic to secondary Region (control plane action)

  • Make read replica in secondary primary or attempting same action in primary Region (control plane action)

Resources

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