how can we make http request from host server to endpoint inside docker container

Question

I want to make http request from server running on localhost currently to api endpoint inside running container. I can't use portmapping as I am creating multiple containers one container per request.

this is how my code looks I am using dockerode create,run,stop and delete container for each request. Container creation and run happens successfully but axios request gets timed out. Is there any solution for this?

 const data = await request.json();
    const { language, program, inputs } = data;
    const docker = new Docker();
    const containerId = v4();
    // 1. I am trying to spin new container using dockerode on each request
    const container = await docker.createContainer({
      Image: "project-name",
      name: containerId,
    });
    await container.start();
    const containerInfo = await container.inspect();
    const ipAddress = containerInfo.NetworkSettings.IPAddress;
    const containerUrl = `http://${ipAdress}/api/run`;
    // 2 .Send code as input to that container's api/run endpoint (Where compiler logic is)

    const response = await axios.post(containerUrl, data);
    // 3. Then stop and remove after getting output
    await container.stop();
    await container.remove();

Answer 1

Except in one very specific host setup, you can't access the container-private IP addresses. You need to publish a port and you need to access the container through its published port. However, you don't have to pick a port yourself; if you don't assign a port then Docker will choose an unused port on its own. (In docker run syntax, this is equivalent to docker run -p 12345 with only a container port number and nothing else.)

docker.createContainer({
  Image: "project-name",
  Name: containerId,
  HostConfig: {
    PortBindings: {
      "80/tcp": [ {} ]
    }
  }
});

Now when you inspect the container, the PortBindings value will be filled in.

const containerInfo = await container.inspect();
const host = 'localhost'; // but see below
const port = containerInfo.HostConfig.PortBindings['80/tcp'][0].HostPort;
const containerUrl = `http://${host}:${port}/api/run`;

The host value is harder to determine programmatically. If your application is running on plain Docker on a native-Linux host, or on Docker Desktop, then localhost will be right. If this application itself is running inside a container with access to the host's Docker socket, you will need host.docker.internal or a similar value. I generally use a Minikube VM in my day job, and its minikube ip address is what I need. You can also set up to use a remote Docker daemon and the host name will be something else entirely.

As a comment suggests, I might rethink this approach. Launching a container per request is actually kind of expensive, there are a lot of lifecycle issues to think about (what happens to the container if the main process creashes), and launching containers implies unrestricted root-level access to the host. I also hinted at some environment-specific differences in the previous paragraph, and this code won't run at all in non-Docker container environments like Kubernetes. If you can set up a single long-running server and make HTTP requests to that, it will be much more maintainable (and much easier to actually run).