How to wait for MSSQL in Docker Compose?

Question

I have a service (an ASP.NET Core Web application) that depends on MSSQL. The services are orchestrated using Docker compose, and I want docker compose to first start the database and wait for it to be ready before running my service. For that, I am defining the docker-compose.yml as:

version: '3.7'  services:    sql.data:     container_name: db_service     image: microsoft/mssql-server-linux:2017-latest     healthcheck:       test: ["CMD", "/opt/mssql-tools/bin/sqlcmd", "-S", "http://localhost:1433", "-U", "sa", "-P", "Pass_word", "-Q", "SELECT 1", "||", "exit 1"]    my_service:     container_name: my_service_container     image: ${DOCKER_REGISTRY-}my_service     build:       context: .       dockerfile: MyService/Dockerfile     depends_on:       - sql.data 

With this health-check, Docker compose does not wait for the database service to be ready, and starts my_service immediately after, and, as expected, my_service fails connecting to the database. Part of the log is:

Recreating db_service ... done Recreating my_service_container ... done Attaching to db_service, my_service_container  my_service_container | info: ...Context[0] my_service_container |       Migrating database associated with context Context my_service_container | info: Microsoft.EntityFrameworkCore.Infrastructure[10403] my_service_container |       Entity Framework Core 3.1.1 initialized 'Context' using provider 'Microsoft.EntityFrameworkCore.SqlServer' with options: MigrationsAssembly=MyService my_service_container | fail: Context[0] my_service_container |       An error occurred while migrating the database used on context Context my_service_container | Microsoft.Data.SqlClient.SqlException (0x80131904): 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: 40 - Could not open a connection to SQL Server) ... exception details ... my_service_container | ClientConnectionId:00000000-0000-0000-0000-000000000000 my_service_container exited with code 0 db_service | 2020-03-05 05:45:51.82 Server      Microsoft SQL Server 2017 (RTM-CU13) (KB4466404) - 14.0.3048.4 (X64)         Nov 30 2018 12:57:58         Copyright (C) 2017 Microsoft Corporation         Developer Edition (64-bit) on Linux (Ubuntu 16.04.5 LTS) 2020-03-05 05:45:51.82 Server      UTC adjustment: 0:00 2020-03-05 05:45:51.82 Server      (c) Microsoft Corporation. 2020-03-05 05:45:51.82 Server      All rights reserved. 2020-03-05 05:45:51.82 Server      Server process ID is 4120. 2020-03-05 05:45:51.82 Server      Logging SQL Server messages in file '/var/opt/mssql/log/errorlog'. 2020-03-05 05:45:51.82 Server      Registry startup parameters:          -d /var/opt/mssql/data/master.mdf          -l /var/opt/mssql/data/mastlog.ldf          -e /var/opt/mssql/log/errorlog 

As shown in the logs, the docker compose first starts the DB, but does not wait for it become ready before running my service.

I tried different syntax for the healthcheck, e.g.,:

test: /opt/mssql-tools/bin/sqlcmd -S http://localhost:1433 -U sa -P ${SA_PASSWORD} -Q "SELECT 1" || exit 1 

But neither worked as expected.

I have checked the following sources online, but using neither I was able to solve the problem:

• stackoverflow answer
• github comment
• github sample

Is this functionality even supported in version 3.7? because of this confusing comment

---

Question

Any thoughts on how best I can wait for MSSQL service to start?