title: kops create cluster inside existing AWS vpc and subnets
body: <p>I am having a trouble creating a kubernets using kops inside existing AWS vpc and subnets.
  I have an existing vpc with the following CIDR blocks:</p>
  
  <p><strong>IPv4 CIDR:</strong> 10.10.16.0/20</p>
  
  <p>And in that VPC I have my subnets with their assigned CIDR blocks:</p>
  
  <p><strong>SubnetDatabaseA:</strong> 10.10.23.0/24</p>
  
  <p><strong>SubnetDatabaseB:</strong> 10.10.24.0/24</p>
  
  <p><strong>SubnetDatabaseC:</strong> 10.10.20.0/24</p>
  
  <p>And so on...</p>
  
  <p>when trying to create the cluster using kops I get this error:</p>
  
  <pre><code> error running task "Subnet/ap-southeast-2a.clusters.dev1.k8s.local" (9m58s remaining to succeed): error creating subnet: InvalidSubnet.Conflict: The CIDR '10.10.18.0/23' conflicts with another subnet
          status code: 400, request id: 252367d1-d693-47b9-a6c5-a44908a0f6f7
  </code></pre>
  
  <p>Which means that one of my subnets is already using that IP range.</p>
  
  <p>How can I assign kops to use a specific CIDR of my choice?</p>
  
  <p>Because I can see that every time I try to create the cluster it assigns a different CIDR (example- CIDR                    10.10.18.0/23)?</p>