I try to containerise my ASP.NET WebAPI with a PostgreSQL database with Docker but it won’t.

I have this connection string definition in appsettings.json:

"ConnectionStrings": {
  "EShopConnectionString": "Host=eshop.database;Port=5432;Database=eshop;User Id=postgres;Password=superuser;"
}

Dockerfile for WebAPI project is

FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS base
WORKDIR /app
EXPOSE 5000

FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
WORKDIR /src
COPY ["EShop.Web/EShop.Web.csproj", "EShop.Web/"]
COPY ["EShop.Application/EShop.Application.csproj", "EShop.Application/"]
COPY ["EShop.Domain/EShop.Domain.csproj", "EShop.Domain/"]
COPY ["EShop.Infrastructure/EShop.Infrastructure.csproj", "EShop.Infrastructure/"]
RUN dotnet restore "./EShop.Web/EShop.Web.csproj"
COPY . .
WORKDIR "/src/EShop.Web"
RUN dotnet build "EShop.Web.csproj" -c Release -o /app/build

FROM build AS publish
RUN dotnet publish "EShop.Web.csproj" -c Release -o /app/publish /p:UseAppHost=false

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "EShop.Web.dll"]

And my docker-compose file looks like this:

services:

  eshop.web:
    image: eshop.backend:v1
    container_name: EShop.Backend
    restart: always
    build:
      context: .
      dockerfile: ./Dockerfile
    ports:
      - 5000:5000
    networks:
      - eshop_network
    depends_on:
      -  eshop.database
    environment:
      # - ConnectionStrings__EShopConnectionString=Host=eshop.database;Port=5432;Database=eshop;User Id=postgres;Password=superuser;
      - ASPNETCORE_ENVIRONMENT=Development
      - ASPNETCORE_HTTP_PORTS=5000

  eshop.database:
    image: postgres:latest
    container_name: EShop.Database
    environment:
      - POSTGRES_DB=eshop
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=superuser
    volumes:
      - ./.containers/eshop-db:/var/lib/postgresql/data
    ports:
      - 5432:5432
    networks:
      - eshop_network

You can notice that I made a comment on a line in the docker-compose file with connection string. If I try to run containers this way my WebAPI says Failed to connect to 127.0.0.1:5432. But if I uncomment that line and left the connection string in appsettings.json like “”, WebAPI will successfully connect to the database. Why so?