Concepts
DNS Failover utilizes Amazon Route 53 to redirect traffic from unhealthy instances or endpoints to healthy ones. It works by continuously checking the health of your website or application endpoints and, if an outage is detected, Route 53 will reroute traffic to pre-configured healthy endpoints.
For example, imagine you have two EC2 instances in separate Availability Zones. If one fails, Route 53 can redirect traffic to the healthy instance, minimizing downtime.
Multi-AZ Deployments for RDS
Amazon Relational Database Service (RDS) offers Multi-AZ deployments for high availability. This feature automatically provisions and maintains a synchronous standby replica in a different Availability Zone. The data is replicated to this standby to enable failover without intervention in the event of an outage or planned maintenance.
A comparison of RDS deployment types could be:
| Deployment Type | Use Case | Availability | Cost |
|---|---|---|---|
| Single-AZ | Development/testing | Low to moderate | Lower |
| Multi-AZ | Production workloads | High availability | Higher |
For a Multi-AZ deployment, the switching process during failover is automatic, and application changes are typically not required.
Auto Scaling
Auto Scaling ensures that you maintain application availability. It can detect when an instance is unhealthy, terminate it, and launch a new one. You can define desired capacity, minimum and maximum number of instances, and scaling strategies.
You might configure an Auto Scaling policy like this:
{
“AutoScalingGroupName”: “MyAutoScalingGroup”,
“PolicyName”: “ScaleOut”,
“AdjustmentType”: “ChangeInCapacity”,
“ScalingAdjustment”: 1,
“Cooldown”: 300
}
This JSON snippet defines a scaling policy that increases the number of instances in the group by 1 after a cooldown period of 300 seconds.
Cross-Region Failover
You can design your architecture to failover across AWS regions for extremely high availability. This strategy involves running instances in multiple regions and using Route 53 or other DNS services to switch traffic between regions during a failover scenario.
An example scenario might involve primary infrastructure in the US West (Oregon) region and a failover setup in the US East (N. Virginia) region. You’d have a Route 53 health check and failover configuration that would re-route traffic from Oregon to N. Virginia if the primary setup failed.
Elastic IP and Load Balancers
AWS’s Elastic IP addresses are static IP addresses designed for dynamic cloud computing. By associating an Elastic IP to a healthy instance, you can facilitate a quick failover since the IP address does not change even if the underlying instances do.
Also, AWS Elastic Load Balancing (ELB) automatically distributes incoming application traffic across multiple targets, such as EC2 instances, containers, and IP addresses. When an instance fails, the ELB removes it from the pool and reroutes traffic to the remaining healthy instances.
You can use ELBs with Auto Scaling Groups to ensure that a minimum number of healthy instances are always serving traffic.
Conclusion
The failover strategies in AWS allow a solutions architect to design resilient, high-availability systems capable of withstanding instance failures, AZ disruptions, and even full region outages. It is essential to consider the balance between cost and availability requirements when designing your failover approach to suit your application’s needs. By combining DNS routing, Multi-AZ RDS deployments, Auto Scaling, cross-region strategies, and the judicious use of Elastic IPs and ELBs, you can ensure that your AWS-hosted applications are robust against a variety of failure modes.
Answer the Questions in Comment Section
True/False: A failover strategy generally involves switching to a redundant or standby computing infrastructure.
Answer: True
Explanation: Failover strategies usually involve automatically switching over to a standby database, server, or network upon the failure or abnormal termination of the previously active application, server, network, or system.
True/False: AWS Elastic Beanstalk provides built-in failover features across multiple AWS Regions.
Answer: False
Explanation: AWS Elastic Beanstalk does not inherently provide failover features across multiple AWS Regions. You would need to implement a custom solution for regional failover.
Which AWS service provides a failover mechanism for incoming user traffic based on health checks?
- A) AWS Lambda
- B) AWS Elastic Beanstalk
- C) ELB (Elastic Load Balancing)
- D) AWS Config
Answer: C) ELB (Elastic Load Balancing)
Explanation: ELB automatically distributes incoming application traffic across multiple targets and performs health checks. It can reroute traffic if a backend target fails a health check.
True/False: Using Amazon RDS Multi-AZ deployments can help in providing high availability and failover support for database instances.
Answer: True
Explanation: Amazon RDS Multi-AZ deployments provide high availability and failover support by automatically replicating the data to a standby instance in a different Availability Zone.
What does Amazon Route 53 use to monitor the health of your resources and perform failover?
- A) Resource tagging
- B) Health checks
- C) Security groups
- D) Elastic Beanstalk
Answer: B) Health checks
Explanation: Amazon Route 53 uses health checks to monitor the health of your resources and to route traffic only to healthy endpoints or perform failover when an endpoint is unhealthy.
Multiple select: Which of the following AWS services provide features to support failover? (Select TWO)
- A) AWS Lambda
- B) Amazon RDS
- C) Amazon Redshift
- D) Amazon Route 53
- E) AWS Direct Connect
Answer: B) Amazon RDS, D) Amazon Route 53
Explanation: Amazon RDS Multi-AZ deployments provide failover capability for database instances. Amazon Route 53 can handle DNS failover and traffic routing policies.
True/False: Failback is the process of restoring a system, component, or service as the primary resource once the primary failure has been fixed.
Answer: True
Explanation: Failback is the process of returning the operation to the primary system or component after the failover system has taken over during an outage.
What does Amazon S3 Cross-Region Replication (CRR) primarily provide?
- A) Failover capabilities
- B) Data encryption
- C) Compliance requirements satisfaction
- D) Data redundancy and geographical expansion
Answer: D) Data redundancy and geographical expansion
Explanation: Amazon S3 CRR is used to replicate data across different AWS Regions for data redundancy and geographical expansion, not primarily for failover capabilities.
True/False: AWS CloudFormation provides automatic failover capabilities for your infrastructure deployments.
Answer: False
Explanation: AWS CloudFormation allows you to model, provision, and manage AWS resources, but it does not provide automatic failover capabilities; you need to design this within your template or manage it with other services.
When configuring Amazon Route 53 with an active-active failover configuration, what is expected?
- A) Traffic is distributed to multiple regions at all times.
- B) Traffic is sent to a secondary region only if the primary region fails.
- C) Route 53 monitors the health checks and routes traffic to a single active region.
- D) Route 53 does not support multiple region traffic distribution.
Answer: A) Traffic is distributed to multiple regions at all times.
Explanation: In an active-active failover configuration, all regions serve traffic under normal operations, but if one region becomes unhealthy, Route 53 will distribute its traffic among the healthy regions.
What is the primary purpose of AWS Auto Scaling?
- A) Decrease response time
- B) Increase fault tolerance
- C) Provide VPN connectivity
- D) Reduce data transfer costs
Answer: B) Increase fault tolerance
Explanation: AWS Auto Scaling ensures that you have the correct number of EC2 instances available to handle the load on your application, increasing fault tolerance.
True/False: AWS Storage Gateway provides a failover feature for on-premises to AWS data replication.
Answer: True
Explanation: AWS Storage Gateway offers storage and data replication to AWS from on-premises environments, supporting hybrid cloud storage and providing for failover capabilities.
Thanks for the detailed tutorial on AWS Certified Solutions Architect – Associate (SAA-C03). The failover strategies were well explained.
Can someone explain the difference between an active-active and active-passive failover strategy in AWS?
I appreciate how the blog covered failover strategies. This is critical for high availability systems.
Is it best to use Route 53 for DNS-based failover with AWS, or are there better alternatives?
Thanks! This helped me understand how to design more resilient architectures on AWS.
I used the info from the blog to set up my first active-active failover system in AWS!
The content on Automated Failover was very informative. Thanks!
How does ELB help in achieving failover within the AWS environment?