Creating security groups

NuGet packages:

Programming elements:

using System;
using System.Threading.Tasks;
using System.Collections.Generic;
using Amazon.EC2;
using Amazon.EC2.Model;

namespace EC2CreateSecGroup
{
  // = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
  // Class to create a security group
  class Program
  {
    private const int MaxArgs = 2;

    static async Task Main(string[] args)
    {
      // Parse the command line and show help if necessary
      var parsedArgs = CommandLine.Parse(args);
      if(parsedArgs.Count == 0)
      {
        PrintHelp();
        return;
      }
      if(parsedArgs.Count > MaxArgs)
        CommandLine.ErrorExit("\nThe number of command-line arguments is incorrect." +
          "\nRun the command with no arguments to see help.");

      // Get the application arguments from the parsed list
      var groupName = CommandLine.GetArgument(parsedArgs, null, "-g", "--group-name");
      var vpcID = CommandLine.GetArgument(parsedArgs, null, "-v", "--vpc-id");
      if(string.IsNullOrEmpty(groupName))
        CommandLine.ErrorExit("\nYou must supply a name for the new group." +
          "\nRun the command with no arguments to see help.");
      if(!string.IsNullOrEmpty(vpcID) && !vpcID.StartsWith("vpc-"))
        CommandLine.ErrorExit($"\nNot a valid VPC ID: {vpcID}");

      // groupName has a value and vpcID either has a value or is null (which is fine)
      // Create the new security group and display information about it
      var securityGroups =
        await CreateSecurityGroup(new AmazonEC2Client(), groupName, vpcID);
      Console.WriteLine("Information about the security group(s):");
      foreach(var group in securityGroups)
      {
        Console.WriteLine($"\nGroupName: {group.GroupName}");
        Console.WriteLine($"GroupId: {group.GroupId}");
        Console.WriteLine($"Description: {group.Description}");
        Console.WriteLine($"VpcId (if any): {group.VpcId}");
      }
    }


    //
    // Method to create a new security group (either EC2-Classic or EC2-VPC)
    // If vpcID is empty, the security group will be for EC2-Classic
    private static async Task<List<SecurityGroup>> CreateSecurityGroup(
      IAmazonEC2 ec2Client, string groupName, string vpcID)
    {
      // See if one or more security groups with that name
      // already exist in the given VPC. If so, return the list of them.
      var securityGroups = await FindSecurityGroups(ec2Client, groupName, vpcID);
      if (securityGroups.Count > 0)
      {
        Console.WriteLine(
          $"\nOne or more security groups with name {groupName} already exist.\n");
        return securityGroups;
      }

      // If the security group doesn't already exists, create it.
      var createRequest = new CreateSecurityGroupRequest{
        GroupName = groupName
      };
      if(string.IsNullOrEmpty(vpcID))
      {
        createRequest.Description = "Security group for .NET code example (no VPC specified)";
      }
      else
      {
        createRequest.VpcId = vpcID;
        createRequest.Description = "Security group for .NET code example (VPC: " + vpcID + ")";
      }
      CreateSecurityGroupResponse createResponse =
        await ec2Client.CreateSecurityGroupAsync(createRequest);

      // Return the new security group
      DescribeSecurityGroupsResponse describeResponse =
        await ec2Client.DescribeSecurityGroupsAsync(new DescribeSecurityGroupsRequest{
          GroupIds = new List<string>() { createResponse.GroupId }
        });
      return describeResponse.SecurityGroups;
    }


    //
    // Method to determine if a security group with the specified name
    // already exists in the VPC
    private static async Task<List<SecurityGroup>> FindSecurityGroups(
      IAmazonEC2 ec2Client, string groupName, string vpcID)
    {
      var request = new DescribeSecurityGroupsRequest();
      request.Filters.Add(new Filter{
        Name = "group-name",
        Values = new List<string>() { groupName }
      });
      if(!string.IsNullOrEmpty(vpcID))
        request.Filters.Add(new Filter{
          Name = "vpc-id",
          Values = new List<string>() { vpcID }
        });

      var response = await ec2Client.DescribeSecurityGroupsAsync(request);
      return response.SecurityGroups;
    }


    //
    // Command-line help
    private static void PrintHelp()
    {
      Console.WriteLine(
        "\nUsage: EC2CreateSecGroup -g <group-name> [-v <vpc-id>]" +
        "\n  -g, --group-name: The name you would like the new security group to have." +
        "\n  -v, --vpc-id: The ID of a VPC to which the new security group will belong." +
        "\n     If vpc-id isn't present, the security group will be" +
        "\n     for EC2-Classic (if your AWS account supports this)" +
        "\n     or will use the default VCP for EC2-VPC.");
    }
  }


  // = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
  // Class that represents a command line on the console or terminal.
  // (This is the same for all examples. When you have seen it once, you can ignore it.)
  static class CommandLine
  {
    //
    // Method to parse a command line of the form: "--key value" or "-k value".
    //
    // Parameters:
    // - args: The command-line arguments passed into the application by the system.
    //
    // Returns:
    // A Dictionary with string Keys and Values.
    //
    // If a key is found without a matching value, Dictionary.Value is set to the key
    //  (including the dashes).
    // If a value is found without a matching key, Dictionary.Key is set to "--NoKeyN",
    //  where "N" represents sequential numbers.
    public static Dictionary<string,string> Parse(string[] args)
    {
      var parsedArgs = new Dictionary<string,string>();
      int i = 0, n = 0;
      while(i < args.Length)
      {
        // If the first argument in this iteration starts with a dash it's an option.
        if(args[i].StartsWith("-"))
        {
          var key = args[i++];
          var value = key;

          // Check to see if there's a value that goes with this option?
          if((i < args.Length) && (!args[i].StartsWith("-"))) value = args[i++];
          parsedArgs.Add(key, value);
        }

        // If the first argument in this iteration doesn't start with a dash, it's a value
        else
        {
          parsedArgs.Add("--NoKey" + n.ToString(), args[i++]);
          n++;
        }
      }

      return parsedArgs;
    }

    //
    // Method to get an argument from the parsed command-line arguments
    //
    // Parameters:
    // - parsedArgs: The Dictionary object returned from the Parse() method (shown above).
    // - defaultValue: The default string to return if the specified key isn't in parsedArgs.
    // - keys: An array of keys to look for in parsedArgs.
    public static string GetArgument(
      Dictionary<string,string> parsedArgs, string defaultReturn, params string[] keys)
    {
      string retval = null;
      foreach(var key in keys)
        if(parsedArgs.TryGetValue(key, out retval)) break;
      return retval ?? defaultReturn;
    }

    //
    // Method to exit the application with an error.
    public static void ErrorExit(string msg, int code=1)
    {
      Console.WriteLine("\nError");
      Console.WriteLine(msg);
      Environment.Exit(code);
    }
  }

}