Docker Container: Unable to connect to SQL Server by name

Question

I created two container on the same network and one of them as a Sql Server instance running. In the other container (with SQL Tools) i'm able to connect to the SQL using the IP Address, but if i swith to machine name it fails.

I already tried do ping the machine and the dns is solving the right IP, i also tried dnslookup and it's also working. Does anyone as a clue on how to fix this?

Full test scenario:

1. Created new network

   docker network create --driver=bridge specsnet
   

2. Run SQL Container

   docker run -e 'ACCEPT_EULA=Y' -e 'SA_PASSWORD=Password!123456' -p 1401:1433 -d --name=TestDBServer --net=specsnet --rm microsoft/mssql-server-linux:latest
   

3. Run New Container with SQL Tools (to test connection)

   docker run -it --net=specsnet --rm --entrypoint "bash" mcr.microsoft.com/mssql-tools:latest
   

4. Loaded some tools for troubleshooting (into SQL Tools container)

   apt-get update | apt-get install telnet -y | apt-get install iputils-ping -y | apt-get install dnsutils -y | apt-get install nmap -y | apt-get install nano -y
   

5. Test Connection with IP (Success - IP was 172.18.0.2)

   sqlcmd -S tcp:172.18.0.2,1433 -U sa -P 'Password!123456'
   

6. Test Connection with Name (Fails)

   sqlcmd -S tcp:TestDBServer,1433 -U sa -P 'Password!123456'
   

Answer 1

So as Bjoern suggested i created a docker compose file and after doing some test i realized the issue was not fixed.

Then i started to manipulate the file, tweaking the properties, and discovered the problem was on the SQL container name (the container name had upper case letters). I set the SQL container name to "testdbserver" and everything worked fine.

1. Docker Compose File

   version: '2'
   services:
     testdbserver:
       image: microsoft/mssql-server-linux:latest
       ports:
         ["1401:1433"]
       environment:
         SA_PASSWORD: Password!123456
         ACCEPT_EULA: Y
       networks:
         - specsnet
   
     sqltools:
       image: mcr.microsoft.com/mssql-tools:latest
       depends_on:
         - testdbserver
       networks:
         - specsnet
   
   networks:
     specsnet:
       driver: bridge
       ipam:
        config:
          - subnet: 10.5.0.0/16
            gateway: 10.5.0.1
   

2. Start SQL Tools Container on Bash Mode

   docker-compose run sqltools bash
   

3. Execute SQL Test Connection (works now)

   sqlcmd -S tcp:testdbserver,1433 -U sa -P 'Password!123456'