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?

Answer 1

After searching and trying many different scenarios, I was able to add waiting using the following composer file. This is for asp.net core solution. The key is that you have to overwrite entrypoint if it is specified in dockerfile. Also, you need to make sure to save "wait-for-it.sh" LF as line ending instead of CRLF, otherwise you'll get the error of file not found.

The dockerfile should have the following (download it from here: https://raw.githubusercontent.com/vishnubob/wait-for-it/master/wait-for-it.sh, make sure to save the file):

COPY ./wait-for-it.sh /wait-for-it.sh
RUN chmod +x wait-for-it.sh

docker-compose.yml

version: '3.7'

services:

  vc-db:
    image: mcr.microsoft.com/mssql/server:latest
    ports:
      - "${DOCKER_SQL_PORT:-1433}:1433"
    expose:  
      - 1433  
    environment: 
      - ACCEPT_EULA=Y
      - MSSQL_PID=Express
      - SA_PASSWORD=v!rto_Labs!
    networks:
      - virto

  vc-platform-web:
    image: virtocommerce/platform:${DOCKER_TAG:-latest}
    ports:
      - "${DOCKER_PLATFORM_PORT:-8090}:80"
    environment:
      - ASPNETCORE_URLS=http://+
    depends_on:
      - vc-db
    entrypoint: ["/wait-for-it.sh", "vc-db:1433", "-t", "120", "--", "dotnet", "VirtoCommerce.Platform.Web.dll"]
    networks:
      - virto