Monday 26 October 2015

Register/Deregister EC2 Servers under ELB using AWS .NET Toolkit

I have been working with AWS toolkit for some time in last week. I prepared some tools to automate our infra team tasks and for our internal development and testing purpose.

Here I will show you how to register/de-register EC2 instances with Elastic Load Balancer programmatically using AWS .NET toolkit.

First get your awsSecretAccessKey and awsAccessKey,


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 string awsSecretAccessKey = ConfigurationManager.AppSettings["awsSecretAccessKey"];
 string awsAccessKey = ConfigurationManager.AppSettings["awsAccessKey"];

Note: The user account you use here for Secret Key and Access Key must have full access to EC2 service of AWS

Create EC2 Client,


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 var client = AWSClientFactory.CreateAmazonElasticLoadBalancingClient(awsAccessKey, awsSecretAccessKey, RegionEndpoint.USWest2);

Make sure you specify correct RegionEndPoint where your EC2 instances exist. Here I have used USWest2 region end point.

Now lets check whether the instance you want to register/de-register already exist under the given ELB.

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DescribeLoadBalancersResponse loadBalancers = client.DescribeLoadBalancers(new DescribeLoadBalancersRequest
                        {
                            LoadBalancerNames = new List<string>() { ELBName }
                        });
                        if (loadBalancers != null && loadBalancers.LoadBalancerDescriptions.Count > 0)
                        {
                            //Instance to add in ELB
                            Amazon.ElasticLoadBalancing.Model.Instance EC2Instance = new Amazon.ElasticLoadBalancing.Model.Instance(InstanceId);

                            List<Amazon.ElasticLoadBalancing.Model.Instance> registeredInstances = loadBalancers.LoadBalancerDescriptions.FirstOrDefault().Instances;

                            if (registeredInstances == null)
                                registeredInstances = new List<Amazon.ElasticLoadBalancing.Model.Instance>();

                            //Check if the current instance to be added exists in already registered instances of elb
                            if (registeredInstances.Any(instance => instance.InstanceId == EC2Instance.InstanceId))
                            {
                                InstanceExists = true;
                            }
                        }

If the instance already exist under ELB then let's de-register it,


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if(InstanceExists)
    {
        client.DeregisterInstancesFromLoadBalancer(new DeregisterInstancesFromLoadBalancerRequest
             {
                  Instances = new List<Amazon.ElasticLoadBalancing.Model.Instance> { EC2Instance  },
                                LoadBalancerName = ELBName
             });
    }

If the instance does not exist under ELB then let's register it,


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 if (!InstanceExists)
         {
           client.RegisterInstancesWithLoadBalancer(new RegisterInstancesWithLoadBalancerRequest
                 {
                       Instances = new List<Amazon.ElasticLoadBalancing.Model.Instance> { EC2Instance },
                                    LoadBalancerName = ELBName
                 });
         }

Here is the full code for registering/de-registering EC2 instances with an elastic load balancer. The idea here is to attach a single server at a time.


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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Amazon;
using Amazon.EC2.Model;
using Amazon.ElasticLoadBalancing.Model;
using System.Web.Services;
using System.Configuration;

public string RegisterServerToLoadBalancer(string ELBName, string InstanceName)
    {
        try
        {
          string message = string.Empty;
          string awsSecretAccessKey = ConfigurationManager.AppSettings["awsSecretAccessKey"];    
          string awsAccessKey = ConfigurationManager.AppSettings["awsAccessKey"];

             if (!string.IsNullOrEmpty(ELBName) && !string.IsNullOrEmpty(InstanceName))                {
                    //Check If the InstanceName is valid
               Amazon.EC2.IAmazonEC2 Ec2Client = AWSClientFactory.CreateAmazonEC2Client(awsAccessKey, awsSecretAccessKey, RegionEndpoint.USWest2);
                    var lstInstances = Ec2Client.DescribeInstances();

                    String InstanceId = lstInstances.Reservations.SelectMany(c => c.Instances.Where(p => p.Tags.Any(d => d.Value.Equals(InstanceName, StringComparison.OrdinalIgnoreCase))).Select(k => k.InstanceId)).FirstOrDefault();

                    if (!string.IsNullOrEmpty(InstanceId))
                    {
                        bool InstanceExists = false;
                        var client = AWSClientFactory.CreateAmazonElasticLoadBalancingClient(awsAccessKey, awsSecretAccessKey, RegionEndpoint.USWest2);
                        DescribeLoadBalancersResponse loadBalancers = client.DescribeLoadBalancers(new DescribeLoadBalancersRequest
                        {
                            LoadBalancerNames = new List<string>() { ELBName }
                        });
                        if (loadBalancers != null && loadBalancers.LoadBalancerDescriptions.Count > 0)
                        {
                            //Instance to add in ELB
                            Amazon.ElasticLoadBalancing.Model.Instance EC2Instance = new Amazon.ElasticLoadBalancing.Model.Instance(InstanceId);
                            List<Amazon.ElasticLoadBalancing.Model.Instance> registeredInstances = loadBalancers.LoadBalancerDescriptions.FirstOrDefault().Instances;
                            if (registeredInstances == null)
                                registeredInstances = new List<Amazon.ElasticLoadBalancing.Model.Instance>();
                            //Check if the current instance to be added exists in already registered instances of elb
                            if (registeredInstances.Any(instance => instance.InstanceId == EC2Instance.InstanceId))
                            {
                                InstanceExists = true;
                                registeredInstances = registeredInstances.Where(c => c.InstanceId != EC2Instance.InstanceId).ToList();
                            }
                            //Remove all registered instances from ELB except current instance to be attached
                            if (registeredInstances.Count > 0)
                            {
                                client.DeregisterInstancesFromLoadBalancer(new DeregisterInstancesFromLoadBalancerRequest
                                {
                                    Instances = registeredInstances,
                                    LoadBalancerName = ELBName
                                });
                                //Console.WriteLine("Instances Detached:");
                                //foreach (Amazon.ElasticLoadBalancing.Model.Instance instance in registeredInstances)
                                //{
                                //    Console.WriteLine(instance.InstanceId);
                                //}
                            }
                            if (!InstanceExists)
                            {
                                //Attach current instance
                                client.RegisterInstancesWithLoadBalancer(new RegisterInstancesWithLoadBalancerRequest
                                {
                                    Instances = new List<Amazon.ElasticLoadBalancing.Model.Instance> { EC2Instance },
                                    LoadBalancerName = ELBName
                                });
                                //Console.WriteLine("Instance Attached, ID : " + EC2Instance.InstanceId);
                            }
                            message = "Success";
                        }
                        else
                        {
                            message = "Invalid Load Balancer Name";
                        }
                    }
                    else
                    {
                        message = "Invalid Instance Name";
                    }
                }
                else
                {
                    message = "Specify Elastic Load Balancer Name and Instance Name to Register";
                }
            return message;
        }
        catch(Exception ex)
        {
            return ex.Message;
        }
    }

Hope you like it. More coming soon.
Happy programming :)
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