Connect with database - docker-compose up - sql-server

Question

I'm trying to make one Docker Compose file to up an WEB (reactJS), API (.NET Core 2.1) and an SQL Server instance.
When I init the database and run .NET with dotnet cli, it works (using a connection string Server=localhost). However what I've been googling is that localhost does not work on containers. And when using container I can't get my .NET Core to connect with my SQL Server.
Can anyone shed some light what am I doing wrong?
I have this repo:
https://github.com/lucasgozzi/sagetest
And I'm currently using a branch names 'docker'. Here is my Docker files and composer in case you don't want to clone the repo.
Backend dockerfile:
FROM mcr.microsoft.com/dotnet/core/aspnet:2.1
WORKDIR /app
FROM mcr.microsoft.com/dotnet/core/sdk:2.1
WORKDIR /src
COPY . .
RUN dotnet restore "./Api/Api.csproj"
RUN dotnet build "Api/Api.csproj" -c Release -o /app/build
RUN dotnet publish "Api/Api.csproj" -c Release -o /app/publish
EXPOSE 5000
WORKDIR /app/publish
ENTRYPOINT ["dotnet", "Api.dll"]
Frontend dockerfile:
# base image
FROM node:12.2.0-alpine
# set working directory
WORKDIR /app
EXPOSE 3000
# add `/app/node_modules/.bin` to $PATH
ENV PATH /app/node_modules/.bin:$PATH
# install and cache app dependencies
COPY . .
RUN npm install --silent
RUN npm install react-scripts -g --silent
# start app
CMD ["npm", "start"]
Docker compose:
version: '3.1'
services:
api:
container_name: "teste-sage-api"
image: 'teste-sage-api'
build:
context: ./backend
dockerfile: Dockerfile
volumes:
- ./backend:/var/www/backend
ports:
- "5000:5000"
depends_on:
- "database"
networks:
- sagetest-network
web:
container_name: "teste-sage-web"
image: 'teste-sage-web'
build:
context: ./frontend_react
dockerfile: Dockerfile
ports:
- "3000:3000"
depends_on:
- "api"
networks:
- sagetest-network
database:
container_name: "sql-server"
image: "mcr.microsoft.com/mssql/server"
environment:
SA_PASSWORD: "Teste#123"
ACCEPT_EULA: "Y"
ports:
- "1433:1433"
networks:
- sagetest-network
networks:
sagetest-network:
driver: bridge

Answer 1

You can access the database form your containers on the service name, in your case this will be database. But you need to make sure that the database container is up and running before trying to connect to it. depends_on is not enough for this case. you may need to implement a waitfor in your dotnet container. check this for more info https://docs.docker.com/compose/startup-order/