Troubleshooting Amazon ECS TaskFailedToStart errors

The following are some TaskFailedToStart error messages and actions that you can take to fix the errors.

Unexpected EC2 error while attempting to Create Network Interface with public IP assignment enabled in subnet 'subnet-id

This happens when a Fargate task that uses the aswsvpc network mode and runs in a subnet with a public IP address, and the subnet does not have enough IP addresses.

The number of available IP addresses is available on the subnet details page in the Amazon EC2 console, or by using describe-subnets. For more information, see View your subnet in the Amazon VPC User Guide.

To fix this issue, you can create a new subnet to run your task in.

InternalError: <reason>

This error occurs when an ENI attachment is requested. Amazon EC2 asynchronously handles the provisioning of the ENI. The provisioning process takes time. Amazon ECS has a timeout in case there are long wait times or unreported failures. There are times when the ENI is provisioned, but the report comes to Amazon ECS after the failure timeout. In this case, Amazon ECS sees the reported task failure with an in-use ENI.

The selected task definition is not compatible with the selected compute strategy

This error occurs when you chose a task definition with a launch type that does not match the cluster capacity type. For more information, see Amazon ECS launch types. You need to select a task definition that matches the capacity provider assigned to your cluster.

Unable to attach network interface to unused device index

This error occurs when When using awsvpc networking type and there is not enough CPU/memory for the task. First, check the CPU for the instances. For more information, see Amazon EC2 instance type specifications in Amazon EC2 instance types. Take the CPU value for the instance and multiply it by the number of ENIs for the instance. Use that value e in the task definition.