AWS Auto Scaling and Elastic Load Balancing

Today we will explore two critical components of building scalable, high-availability applications on AWS : Auto Scaling and Elastic Load Balancing (ELB). AWS Auto Scaling ensures that you have the right number of EC2 instances running to handle the load for your application while ELB automatically distributes incoming application traffic across multiple targets such as EC2 instances, containers and IP addresses. This blog will cover the fundamentals of Auto Scaling groups, configuring load balancers and best practices for achieving high availability and fault tolerance.

What is AWS Auto Scaling?

AWS Auto Scaling allows you to automatically adjust the number of EC2 instances in your application in response to changing demand. This helps you maintain performance and minimize costs by scaling out (adding instances) when demand increases and scaling in (removing instances) when demand decreases.

Key Features of AWS Auto Scaling

1. Dynamic Scaling : Automatically adjust capacity based on demand.

2. Predictive Scaling : Forecast and scale ahead of predicted traffic spikes.

3. Scheduled Scaling : Predefine scaling actions based on known usage patterns.

4. High Availability : Ensure your application remains available under high traffic.

5. Cost Management : Optimize costs by scaling in when resources are not needed.

What is Elastic Load Balancing?

Elastic Load Balancing (ELB) automatically distributes incoming application traffic across multiple targets to ensure that no single target becomes overwhelmed. ELB increases the fault tolerance of your applications by redirecting traffic to healthy targets and away from unhealthy ones.

Key Features of Elastic Load Balancing

1. Traffic Distribution : Distribute incoming traffic across multiple targets.

2. Health Checks : Monitor the health of targets and route traffic only to healthy ones.

3. Integration with Auto Scaling : Work seamlessly with Auto Scaling groups.

4. Support for Multiple Protocols : HTTP, HTTPS, TCP and UDP.

5. SSL Termination : Manage SSL certificates and terminate SSL connections.

Getting Started with AWS Auto Scaling

Step 1 : Creating a Launch Configuration

A launch configuration is an instance configuration template that an Auto Scaling group uses to launch EC2 instances.

1. Navigate to the EC2 Console :

   • Log in to the AWS Management Console.

   • Search for "EC2" in the AWS services search bar and select it.

2. Create a Launch Configuration :

   • Click "Launch Configurations" in the left navigation pane.

   • Click "Create launch configuration".

   • AMI : Choose an Amazon Machine Image (AMI).

   • Instance Type : Select an instance type (e.g. t2.micro).

   • Configuration Details : Enter a name for the launch configuration.

   • Key Pair : Select an existing key pair or create a new one.

   • Security Groups : Choose an existing security group or create a new one.

   • Click "Create launch configuration".

Step 2 : Creating an Auto Scaling Group

An Auto Scaling group contains a collection of EC2 instances that are treated as a logical grouping for the purposes of automatic scaling and management.

1. Create an Auto Scaling Group :

   • Click "Auto Scaling Groups" in the left navigation pane.

   • Click "Create Auto Scaling group".

   • Group Name : Enter a name for your Auto Scaling group.

   • Launch Configuration : Select the launch configuration created earlier.

   • VPC and Subnets : Select the VPC and subnets where the Auto Scaling group will launch instances.

   • Scaling Policies : Configure scaling policies (e.g. target tracking scaling policy).

   • Health Checks : Choose the health check type (EC2 or ELB).

   • Click "Create Auto Scaling group".

Step 3 : Configuring Scaling Policies

Scaling policies define how your Auto Scaling group should scale in and out.

1. Target Tracking Scaling Policy :

   • In the Auto Scaling group details click "Scaling Policies".

   • Click "Create scaling policy".

   • Policy Type : Select "Target tracking scaling policy".

   • Metric Type : Choose a predefined metric (e.g. Average CPU Utilization).

   • Target Value : Set a target value for the metric (e.g. 50% CPU utilization).

   • Click "Create".

2. Step Scaling Policy (optional) :

   • Click "Create scaling policy".

   • Policy Type : Select "Step scaling policy".

   • Metric : Choose a metric and set thresholds for scaling actions.

   • Click "Create".

Getting Started with Elastic Load Balancing

Step 1 : Creating a Load Balancer

Elastic Load Balancing supports different types of load balancers : Application Load Balancers (ALB), Network Load Balancers (NLB) and Gateway Load Balancers (GWLB). For this example we will use an Application Load Balancer.

1. Navigate to the EC2 Console :

   • Log in to the AWS Management Console.

   • Search for "EC2" in the AWS services search bar and select it.

2. Create an Application Load Balancer :

   • Click "Load Balancers" in the left navigation pane.

   • Click "Create Load Balancer".

   • Load Balancer Type : Select "Application Load Balancer".

   • Name : Enter a name for the load balancer.

   • Scheme : Choose "Internet-facing" or "Internal".

   • Listeners : Set up listeners (e.g. HTTP, HTTPS).

   • VPC and Subnets : Select the VPC and subnets where the load balancer will operate.

   • Security Groups : Select or create a security group.

   • Click "Next : Configure Security Settings".

Step 2 : Configuring Target Groups

A target group routes requests to one or more registered targets (e.g. EC2 instances) using the protocol and port number specified.

1. Create a Target Group :

   • Click "Create target group".

   • Name : Enter a name for the target group.

   • Target Type : Select "Instance".

   • Protocol : Choose a protocol (e.g. HTTP).

   • Port : Enter a port (e.g. 80).

   • VPC : Select the VPC where the targets are located.

   • Click "Next".

2. Register Targets :

   • Select the instances to add to the target group.

   • Click "Include as pending below".

   • Click "Create target group".

Step 3 : Configuring Listeners and Rules

Listeners check for connection requests from clients using the protocol and port you specify and forward requests to one or more target groups based on rules.

1. Configure Listeners :

   • In the load balancer details click "Listeners".

   • Click "Add listener".

   • Protocol and Port : Specify the protocol and port for the listener (e.g. HTTP, port 80).

   • Default Action : Select "Forward to" and choose the target group created earlier.

   • Click "Save".

2. Add Rules (optional) :

   • Click "View/edit rules" under the listener configuration.

   • Add rules to route traffic based on conditions (e.g. URL paths).

   • Click "Save".

Best Practices for High Availability and Fault Tolerance

Step 4 : Multi-AZ Deployments

Deploy your EC2 instances, Auto Scaling groups and load balancers across multiple Availability Zones (AZs) to ensure high availability and fault tolerance.

1. Auto Scaling Group Configuration :

   • In the Auto Scaling group details select "Subnets" under "Network".

   • Choose subnets from multiple AZs.

2. Load Balancer Configuration :

   • When creating the load balancer select subnets from multiple AZs.

Step 5 : Health Checks

Configure health checks to monitor the health of your EC2 instances and ensure that traffic is only routed to healthy instances.

1. Auto Scaling Group Health Checks :

   • In the Auto Scaling group details select "Health checks".

   • Choose "ELB" health checks to integrate with your load balancer.

2. Load Balancer Health Checks :

   • In the target group details configure health check settings (e.g. path, interval, timeout).

Step 6 : Scaling Policies and Cooldown Periods

Define appropriate scaling policies and cooldown periods to avoid excessive scaling actions.

1. Scaling Policies :

   • Set target tracking, step or simple scaling policies based on your application's requirements.

2. Cooldown Periods :

   • Configure cooldown periods to ensure stable scaling behavior.

Step 7 : Monitoring and Alerts

Use Amazon CloudWatch to monitor the performance of your Auto Scaling groups and load balancers and set up alerts to notify you of any issues.

1. CloudWatch Metrics :

   • Monitor metrics such as CPU utilization, request count and healthy/unhealthy host counts.

2. CloudWatch Alarms :

   • Create alarms to trigger notifications or automated actions based on metric thresholds.

Step 8 : Security Best Practices

Ensure that your Auto Scaling groups and load balancers are secure.

1. Security Groups :

   • Define least-privilege security group rules for your instances and load balancers.

2. IAM Roles :

   • Use IAM roles to grant necessary permissions to your Auto Scaling groups and load balancers.

3. SSL/TLS :

   • Terminate SSL/TLS at the load balancer to secure traffic between clients and the load balancer.

Conclusion

AWS Auto Scaling and Elastic Load Balancing are essential components for building scalable, high-availability applications. By understanding how to configure Auto Scaling groups, load balancers and scaling policies you can ensure that your applications can handle varying levels of traffic while maintaining performance and minimizing costs. Follow best practices for multi-AZ deployments, health checks, monitoring and security to achieve robust and fault-tolerant architectures.

Stay tuned for more insights and best practices in our upcoming blog posts.

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Sudha Yadav