Connecting to host Cosmos emulator from Docker container

Question

I have a .net application running in a docker container via docker compose. I'm using a Windows machine with Docker Desktop running Linux containers.

The application connects to a Cosmos instance. The account key is set to the emulator key by default.

Here is the section from docker-compose.yml

  customerapi:
    container_name: mycustomerapi
    image: acr.io/customer-api:master
    ports:
      - "20102:80"
    environment:
      - ASPNETCORE_ENVIRONMENT=Development
      - CosmosOptions__Endpoint=${endpoint}
      - CosmosOptions__DisableSsl=true

If I override the account key and endpoint, I can get the application to connect using a real instance hosted in Azure, but I can't get it to connect to the emulator running on the host machine.

I've tried setting ${endpoint} to the following values with no luck;

• https://host.docker.internal:8081/ Fails after about 5 mins with the error System.Net.Http.HttpRequestException: Connection refused (127.0.0.1:8081).
• https://192.168.10.110:8081/ This is my local IP address. It fails much faster (around 10 seconds) with the same error as above.

I've also tried using network_mode: host with both endpoints.

• https://host.docker.internal:8081/ Fails with the same error as above.
• https://192.168.10.110:8081/ Fails after about 10 seconds with the error System.Net.Http.HttpRequestException: No route to host (192.168.10.110:8081)

Answer 1

I needed to run Cosmos with AllowNetworkAccess

This answer shows how to start the emualtor with the /AllowNetworkAccess argument.
Azure Cosmos DB Emulator on a Local Area Network
Once that was running I was able to use https://host.docker.internal:8081/ and the container sprung to life!