Connecting to MS SQL Server in container

Question

We've got a Python-based app server running on a Linux image. We're trying to connect to a Linux container running SQL Server on port 1433. We're using unixODBC and FreeTDS, and everything works when creating a local network (`docker network create --driver bridge --subnet 172.21.0.0/24 our_network.bridge`), then adding the containers to the network. Then we can access SQL Server's data source by name (`docker run -itd --network=our_network.bridge --name local-mssql microsoft/mssql`), local-mssql in this case. We can `telnet 127.0.0.1 1433`, so the port is open. But using unixODBC command line tool isql (parameters: server name, username, password), this is the result: + isql -v sqlserver sa supersecret
[ISQL]ERROR: Could not SQLConnect
[S1000][unixODBC][FreeTDS][SQL Server]Unable to connect to data source
[01000][unixODBC][FreeTDS][SQL Server]Unknown host machine name. Any idea how we can access to our database?

SebC · Answer

Hey @[deleted], I'm not super familiar with unixODBC, but I can talk about the general network set up. When using Pipelines services, the processes running inside these containers all share a network interface with the main step execution container. This is why you can access everything via localhost / 127.0.0.1, and why there can be no port conflicts between services (can't run nginx and apache on port 80 for example). As a common rule, each service must listen for connections from localhost/127.0.0.1, and the clients should connect to localhost. Is it possible your command isql -v sqlserver sa supersecret is trying to connect to a remote host named 'sqlserver' and not `localhost` ?