The main issue is that when running ECS containers inside LocalStack, they need to be configured to use LocalStack's internal networking to access other AWS services like S3.

1. Configure the ECS container to use LocalStack's internal networking:

• Set the AWS_ENDPOINT_URL environment variable to point to LocalStack's internal endpoint

• Use the LocalStack hostname for S3 access

1. Create a task definition that includes the necessary environment variables and networking configuration

2. Create a service that uses this task definition and connects to the same network as LocalStack

3. In your application code, configure the AWS SDK to use the LocalStack endpoint

4. Make sure your LocalStack container and ECS tasks are on the same network.

5. When creating the S3 bucket in LocalStack, make sure to use the same region and credentials that your ECS task is configured to use