ELB Web Server on VPC

September 6, 2013

aws vpc ruby

The background for this article is mostly spelled out in the last post I did on how to create a SSH Gateway Server on VPC. This builds on that, and shows how to create a public-facing web server on using an Elastic Load Balancer (ELB). However, this article may be run standalone.

Note: In order to create a quick web server, I made an AMI out of a stock Ubuntu 13.04 server that I used sudo apt-get apache2 php5, and then added a info.php script to just get some output about the machine. If you are following along, you can do the same, or configure the web sever however you’d like.

Again, all of my examples will be in ruby using the aws-sdk gem, but the same results can be achieved using any of their other SDKs.

Assumptions

You have a basic undertsanding of AWS
You already have an active AWS account
You have a keypair called key-lab located at ~/.ec2/key-lab.pem (rename where appropriate)
All commands are probably best done in irb, this way you can inspect objects as you go along. Make sure to look at the aws-sdk docs.

Creating the VPC

First, let’s set up the VPC basics like we did with the last article.

    require 'aws-sdk'

    AWS.config(access_key_id: "....", secret_access_key: "....")
    $ec2 = AWS::EC2.new
    $vpc = $ec2.vpcs.create("10.0.0.0/16")

    gateway = $ec2.internet_gateways.create
    gateway.attach($vpc)

    public_route = $vpc.route_tables.first
    public_route.create_route("0.0.0.0/0", internet_gateway: gateway.id)

    public_subnet = $vpc.subnets.create("10.0.0.0/24", availability_zone: "us-east-1d")
    private_subnet = $vpc.subnets.create("10.0.1.0/24", availability_zone: "us-east-1d")

With ELBs in VPC, you give them their own security group. Since this one will accept http traffic, we should open tcp/80 to the world.

    elb_security_group = $ec2.security_groups.create("elb", vpc_id: $vpc.id)
    elb_security_group.authorize_ingress(:tcp, 80, "0.0.0.0/0")

Since the load balancer needs to talk to our web server that will get the private_security_group, we should allow incoming requests on tcp/80 and from elb_security_group through.

    private_security_group = $ec2.security_groups.create("private", vpc_id: $vpc.id)
    private_security_group.authorize_ingress(:tcp, 80, {group_id: elb_security_group.id})

Launching the Instances

Now it’s time to bring up the web server inside the private subnet

    web_server = $ec2.instances.create(
        subnet: private_subnet,
        security_groups: private_security_group,
        availability_zone: "us-east-1d",
        instance_type: "t1.micro",
        key_name: "key-lab",
        image_id: 'ami-efd79886' ## Ubuntu 13.04 amd64 with apache/php running
    )

    ## wait around 30-60 seconds for the instance to launch
    sleep 2 until web_server.status == :running

Creating the Elastic Load Balancer

Finally, create the ELB. We will put it in the public subnet since it needs to communicate to the outside world though the internet gateway. We also specify the elb_security_group and listener.

    web_elb = $elb.load_balancers.create("test-web",
      security_groups: [elb_security_group],
      subnets: [public_subnet],
      listeners: [
        { protocol: :tcp, port: 80, instance_protocol: :tcp, instance_port: 80 }
      ]
    )

After we’ve created the ELB, we need to tell it about the instances that it should use. Normally, you should have servers in multiple availbility zones, but for this demonstration, we’ll just use one.

    web_elb.instances.add(web_server)
    sleep 2 until web_elb.instances.health.first[:state] == "InService"

You might need to wait a bit for the DNS to propagate. sudo dscacheutil -flushcache on OS X may help

Finally, your instance should be up and available through the ELB!

    system("curl -s http://#{web_elb.dns_name}/info.php | grep 'SERVER_ADDR'")
    #  <tr><td class="e">SERVER_ADDR </td><td class="v">10.0.1.12 </td></tr>
    #  <tr><td class="e">_SERVER["SERVER_ADDR"]</td><td class="v">10.0.1.12</td></tr>

Clean-up

Amazon charges you per hour, so if you’re just testing and want to shut everything down, here are some clean-up steps. There’s a mess of dependencies, so you need to do it in a specific order.

    web_server.terminate
    sleep 2 until web_server.status == :terminated
    
    ## Delete ELB
    web_elb.delete
    sleep 2 until web_elb.exists? == false
    
    ## Delete the security groups
    private_security_group.delete
    elb_security_group.delete
    
    ## Delete the subnets
    private_subnet.delete
    public_subnet.delete
    
    ## Get rid of the routes
    public_route.routes.last.delete
    
    ## Detach and delete the Internet Gateway
    gateway.detach($vpc)
    gateway.delete
    
    ## Finally, delete the VPC
    $vpc.delete