Amazon web services – Blazor App in ECS Fails to Connect to SQL Server Container: DNS Resolution Issue

Preview: Currently, the Blazor App is accessible via the internet through the public DNS. While registering through the app (which requires db access), two exceptions are thrown in the broswer:

SocketException: Name or service not known.

SqlException: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: TCP Provider, error: 35 – An internal exception was caught).

Goal: Connect Blazor App running in EC2 instance container to SQL Server running in the same EC2 instance/different container.

What I know:

• Both Containers are running (including EC2 agent) within instance.
• Port 1433 is accessible from any public IP:

• SQL Server container can be pinged from within SQL Server container by its IP Address, but not by its host/container name:

What I’ve tried (condensed):

1. Set proper security group settings:

2. Removed "1433" from connection string for the Server property ("Server=sqlserver,1433;" -> "Server=sqlserver;")

3. Added "hostname" key in the Task Definition JSON:

{
    "family": "blazor_app_task",
    "containerDefinitions": [
        {
            "name": "blazor_app_container",
            "image": "thecodeiackiller/exercise-api-blazorapp:latest",
            "cpu": 205,
            "memory": 307,
            "memoryReservation": 205,
            "portMappings": [
                {
                    "name": "blazor_app_container-8080-tcp",
                    "containerPort": 8080,
                    "hostPort": 80,
                    "protocol": "tcp"
                }
            ],
            "essential": true,
            "environment": [
                {
                    "name": "ASPNETCORE_ENVIRONMENT",
                    "value": "Development"
                },
                {
                    "name": "DB_CONNECTION_STRING",
                    "value": "Server=sqlserver;Database=fitsked;User Id=sa;Password=supahstrongpassword#69;Encrypt=False;TrustServerCertificate=True;MultipleActiveResultSets=true"
                },
                {
                    "name": "AWS_EC2",
                    "value": "true"
                }
            ],
            "mountPoints": [],
            "volumesFrom": [],
            "logConfiguration": {
                "logDriver": "awslogs",
                "options": {
                    "awslogs-group": "/ecs/blazor_app_task",
                    "mode": "non-blocking",
                    "awslogs-create-group": "true",
                    "max-buffer-size": "25m",
                    "awslogs-region": "us-east-1",
                    "awslogs-stream-prefix": "ecs"
                }
            },
            "systemControls": []
        },
        {
            "name": "sqlserver",
            "image": "mcr.microsoft.com/mssql/server:2022-latest",
            "cpu": 1024,
            "memory": 2048,
            "memoryReservation": 1536,
            "portMappings": [
                {
                    "name": "sqlserver-1433-tcp",
                    "containerPort": 1433,
                    "hostPort": 1433,
                    "protocol": "tcp"
                }
            ],
            "essential": true,
            "environment": [
                {
                    "name": "MSSQL_SA_PASSWORD",
                    "value": "supahstrongpassword#69"
                },
                {
                    "name": "ACCEPT_EULA",
                    "value": "Y"
                }
            ],
            "mountPoints": [],
            "volumesFrom": [],
            "hostname": "sqlserver",
            "systemControls": []
        }
    ],
    "taskRoleArn": "arn:aws:iam::448049819404:role/ecsTaskExecutionRole",
    "executionRoleArn": "arn:aws:iam::448049819404:role/ecsTaskExecutionRole",
    "networkMode": "bridge",
    "volumes": [],
    "placementConstraints": [],
    "requiresCompatibilities": [
        "EC2"
    ],
    "cpu": "1536",
    "memory": "3072",
    "runtimePlatform": {
        "cpuArchitecture": "X86_64",
        "operatingSystemFamily": "LINUX"
    }
}