All resources should be in the same security group and VPC.
Create the task definition for the Bold BI application using the following details. Follow this document to learn more about ECS task definitions.
Go to the Cluster and create the service by following below steps: Navigate to = Amazon Elastic Container Service —> Clusters —> Cluster name —> Services —> Create
Follow the document below to create the Load balancer with target group in ECS service
https://docs.aws.amazon.com/AmazonECS/latest/userguide/create-load-balancer.html
Now, create the service.
Once service is Up and running you can access the Application using Application Load Balancer DNS.