Cannot create a Load Balancer in EC2: Error Internal Failure

There are several potential causes for the "Error Internal Failure" when creating a load balancer in EC2. One common reason is that you might be using an IP address that is already assigned or allocated elsewhere in your network, such as a secondary IP address for an EC2 instance. This IP address conflict prevents the load balancer from being set up properly, resulting in a failed state.

To resolve this issue, you should:

1. Check if any of the IP addresses you're trying to use for your load balancer are already allocated elsewhere in your network.
2. De-allocate any conflicting IP addresses and retry the creation process.

If you're creating an internal load balancer, ensure it's placed in the appropriate subnet type. While internal load balancers can technically be placed in public subnets, it's a best practice to place them in private subnets.

If the problem persists after checking for IP conflicts, you might be experiencing a transient issue with the Elastic Load Balancing service. In this case:

1. Wait approximately 15 minutes and try again.
2. If the issue continues, you may need to contact AWS Support for assistance.
   Sources
   Troubleshoot your Network Load Balancer - Elastic Load Balancing
   Troubleshoot a Classic Load Balancer: API errors - Elastic Load Balancing
   Internal ALB is placed in a public subnet. | AWS re:Post