Docker - Mongo DB instance not connecting with application

Question

I am using docker mongo with my aspnet core application but I am unable to make connection with mongodb which is running under container. Although I am able to connect MongoDB compass GUI with MongoDB running under docker But my application is not connecting. Here are my steps

First I pull Mongo DB Image

docker pull mongo:latest

Then I create network bridge for mongo

docker network create --driver bridge mongo_db

Then I run mongo image with bridge network

docker run -d -p 27017:27017 --net=mongo_db --name mongodb mongo

after above steps I created my aspnetcore image file

docker build -t lmsapp/v2 .

FROM mcr.microsoft.com/dotnet/core/sdk:3.1 AS build
WORKDIR /app
EXPOSE 5000
EXPOSE 5001

COPY ["SharedKernal/SharedKernal.csproj", "SharedKernal/"]
COPY ["LMS.Entities/LMS.Entities.csproj", "LMS.Entities/"]
COPY ["LMS.Core/LMS.Core.csproj", "LMS.Core/"]
COPY ["LMS.Infrastructure/LMS.Infrastructure.csproj", "LMS.Infrastructure/"]
COPY ["LMS.Web/LMS.Web.csproj", "LMS.Web/"]

RUN dotnet restore "LMS.Web/LMS.Web.csproj"

COPY . .
WORKDIR "/app/LMS.Web"

CMD [ "/bin/bash","-c","dotnet restore && dotnet watch run" ]

and in the last step I run my custom image using the following command

docker run -d --net=mongo_db --name lms -p 5000:5000 -p 5001:5001 -v "$(pwd):/app".ToLower() -w "/app/LMS.Web" lmsapp/v2

Now when I browse the application I am unable to connect with mongo. Here is my connectionstring

"ConnectionString": "mongodb://localhost:27017"

I tried different verion of connection string but none is working except one

"ConnectionString": "mongodb://0.0.0.0:27017"
"ConnectionString": "mongodb://127.0.0.1:27017"
"ConnectionString": "mongodb://api:27017"

When I find the container IP and try to connect mongo with my application only then it works

"ConnectionString": "mongodb://172.1.8.1:27017"

But I am able to successfully connect my MongoDB compass GUI with mongo instance running in container.

Whats the issue behind all this?

Answer 1

Your connection string should be mongodb://CONTAINER_NAME, so mongodb://mongo in your case.

Here is a command that will work with your setup, and start a mongo client, just to demonstrate the point:

$ docker run --rm -it --net=mongo_db mongo mongo "mongodb://mongodb"

You can make life easier for you if you work with docker compose. Here is a working sample:

volumes:
  mongodb:

services:
  mongo:
    image: mongo
    ports: ["27017:27017"] # only needed if you need access from the host
    volumes:
    - mongodb:/data/db

  client:
    image: mongo
    depends_on: [mongo]
    entrypoint: mongo
    command: mongodb://mongo

Run with:

$ docker-compose up -d mongo
$ docker-compose run client