Since you already have a key, you can connect to your instance by following the steps for using eclipse with an existing key to SSH into your instance.
Here's what you need to do:
1. Open your Eclipse SDK and go to Window->Preferences menu.
2. now navigate to General->Network Connections->SSH2
3. Here you input the location of your key and in private keys field, you provide the key.
4. Now navigate General->RemoteSystem and set your user name for SSH.
- For Amazon Linux instances: ec2-user
- For Ubuntu instance: ubuntu
Now you should be able to connect.