Docker container cannot connect to Autonomous Database

Question

I have a dotnet core project that connects to an Oracle Autonomous Datawarehouse. Running the project through Visual Studio works perfectly. I want to containerise the project, but whenever I run the container, it cannot connect to the ADW, failing with "TNS:could not resolve the connect identifier"

Here is my Dockerfile:

FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY backend.csproj .
RUN dotnet restore
COPY . .
RUN dotnet publish -c release -o /app

FROM mcr.microsoft.com/dotnet/aspnet:6.0
WORKDIR /app
EXPOSE 80
EXPOSE 443
EXPOSE 1522
COPY --from=build /app .
ENTRYPOINT ["dotnet", "backend.dll"]

In my project I created a top level folder named "tns". In there I have everything from the wallet file from my ADW. I have modified the sqlnet.ora file to look like this:

WALLET_LOCATION = (SOURCE = (METHOD = file) (METHOD_DATA = (DIRECTORY="tns")))

Here is my compose file:

version: '3.4'

services: 

  frontend:
    image: pizzafrontend
    build:
      context: frontend
      dockerfile: Dockerfile
    environment: 
      - backendUrl=http://backend
    ports:
      - "5902:80"
    depends_on: 
      - backend
  
  backend:
    image: pizzabackend
    build: 
      context: backend
      dockerfile: Dockerfile
    ports: 
      - "5900:80"
      - "1522:1522"

I tried adding an environment variable TNS_ADMIN="tns" or TNS_ADMIN="src/tns", neither of which made any difference. I am at my wits end with this, I feel I am so close to the answer, so any assistance welcome.

Answer 1

I think you are confusing 2 things:

• Simple communication between 2 containers through 2 ports with TCP or UDP protocol.
• Access to a frontend or a backend over HTTP (what you need)

In docker-compose, "frontend" and "backend" values the local IP of the containers, and thus can only be used for local communication between the exposed ports.

Thus you need one more variable: BACKEND_HOSTNAME. It will values "localhost" if you test locally, and the server IP or domain name if you deploy.

And thus backendUrl values http://$BACKEND_HOSTNAME:5900 if your backend is on port 5900.