We finally got to the bottom of this. Environment variable was right, but there was an old container hanging around in the background confusing the docker network about what should match our proget_db.

We've followed the directions as provided here, but the SQL_CONNECTION_STRING appears to be ignored by the proget container. When a connection string with DB hostname other than "proget-sql" is provided, that host is ignored and proget attempts to reach "proget-sql" anyway. When we spin up SQL server instance on the hostname "proget-sql", we get past DNS resolution, but then fail when trying to authenticate to the instance. All of this combined suggests the documented environment variable is not actually being provided to proget process.

Is there a different approach outside of the provided documentation we should be using instead?

The docker-compose file we're using is the following:

version: '3'

services:
  proget:
    image: proget.inedo.com/productimages/inedo/proget:5.3.7
    restart: unless-stopped
    environment:
      - 'SQL_CONNECTION_STRING=Data Source=proget_db;Initial Catalog=ProGet;User ID=sa;Password=******'
    volumes:
      - packages:/var/proget/packages
      - extensions:/var/proget/extensions
    ports:
      - 80:80

  proget_db:
    image: mcr.microsoft.com/mssql/server:2019-latest
    restart: unless-stopped
    volumes:
      - database:/var/opt/mssql
    ports:
      - 1433:1433
    environment:
      - ACCEPT_EULA=Y
      - MSSQL_SA_PASSWORD=******
      - MSSQL_PID=Express

volumes:
  database:
  packages:
  extensions: