Unable to Connect to the New Linux Based Emulator from a Docker Container (cosmosEmulatorVnextPreview)

[tnguyen2206]

I'm giving the new Linux-based emulator a try and running into an issue when trying to connect to it from a ASP.Net Core 8 app running in a Docker container. The request just times out after a while. I'm able to connect to the emulator from a console app just fine. I ran into the same issue when using the Windows local installed emulator but was able to get past the same issue by passing the /AllowNetworkAccess flag when running the emulator. I don't see any Docker command in this list https://learn.microsoft.com/en-us/azure/cosmos-db/emulator-linux#docker-commands that will allow me to set the AllowNetworkAccess flag. Is allowing network access not supported?

[alaye-ms]

You're right that we don't have the AllowNetworkAccess flag as part of the linux based emulator at this time. However, there might be something you can do with docker to allow for network access.

If you run your containers on the host network using the --network host flag, then they should be able to communicate with each other on localhost. See here for more details: https://docs.docker.com/engine/network/tutorials/host/

Alternatively, if you could try to point your client container to the emulator container using it's docker-assigned IP address (if they are both on the default bridge network). You can get that ip by running docker inspect <container_id>.

[tnguyen2206]

I tried the workarounds but no luck. When running the emulator container using the --network host flag, I could not access the explorer in the browser. When trying to connect to the emulator container using its docker-assigned IP, the request sent from my client app just timed out after a while.

[alaye-ms]

Would you be able to give me more details about how you're running this? Like how are you deploying these containers, what platform are you using, and what's your host OS? Maybe if you could post some output of the commands it could help to debug as well.

Here's how I tested things specifically. Running Docker in WSL Ubuntu on Windows.

docker run --rm --network host mcr.microsoft.com/cosmosdb/linux/azure-cosmos-emulator:vnext-preview
For this workaround I had to turn on the feature on Docker Desktop following this instruction:
"To enable this feature, navigate to the Resources tab in Settings, and then under Network select Enable host networking."

And then also allow networking to WSL from host windows with:
New-NetFirewallRule -DisplayName "WSL" -Direction Inbound -InterfaceAlias "vEthernet (WSL (Hyper-V firewall))" -Action Allow

---

For the bridge network test, I ran the container like this:
docker run --rm mcr.microsoft.com/cosmosdb/linux/azure-cosmos-emulator:vnext-preview
and then ran in a new terminal
docker inspect happy_elion
and got the ip address 172.17.0.2

From there I checked the connection with
docker run -it --rm busybox
inside which I ran
wget 172.17.0.2:8081 -O -
which successfully connected to the endpoint.

[breaker05]

Having the same issue here. When I run the emulator standalone and my Api project standlone as well I can reach the CosmosDb and explorer, however when the two are in the same compose as below the connection just times out. The k-api has the correct connection string too.

k-api can not resolve the k-cosmo

name: k

services:
  
  k-cosmosdb:
    container_name: k-cosmosdb
    image: mcr.microsoft.com/cosmosdb/linux/azure-cosmos-emulator:vnext-preview
    command: --enable-telemetry true
    ports:
      - "8081:8081"
      - "1234:1234"

  k-api:
    container_name: k-api
    build:
      dockerfile: Dockerfile
      args:   
       - DbConfiguration__EndpointUrl=http://k-cosmosdb:8081
    ports:
      - "5180:8080"
    depends_on:
      - k-cosmosdb

[alaye-ms]

I used a modified version of your compose file with just a busybox:

name: k

services:

  k-cosmosdb:
    container_name: k-cosmosdb
    image: mcr.microsoft.com/cosmosdb/linux/azure-cosmos-emulator:vnext-preview
    command: --enable-telemetry false
    ports:
      - "8081:8081"
      - "1234:1234"

  k-api:
    container_name: k-api
    image: busybox
    command: tail -F anything
    environment:
       - EndpointUrl=http://k-cosmosdb:8081
    depends_on:
      - k-cosmosdb

and then connected to the k-api: docker exec -it k-api /bin/sh
and ran wget $EndpointUri -O -
And was able to get a response.

Would you be able to provide me some more details about your app? Like what cosmosdb API does it use, I know .NET and java don't yet support http connection.

[breaker05]

@alaye-ms
This works for me too this way, however that is simply checking if it can reach the container by doing a wget and attempting to connect to the actual emulator.

I am using .NET 8 and Entity Framework. When it attempts to establish a connection that's when it throws the connection refused timeout. This is the case as well when using the --protocol https command flag.