How to access and run command on host from Docker container?

Question

I want to access my host bash from Docker container and run there netstat , then get result of netstat and render it with Python/Flask as HTML page. Here is an example how i've done it without docker container.

from flask import Flask, render_template

app = Flask(__name__)

def get_ports_data():
    import subprocess
    p = subprocess.Popen(['netstat', '-ltup'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    stdout, stderr = p.communicate()
    data = stdout.decode().split('\n')
    return data

@app.route('/')
def index():
    return render_template('index.html', portsdata=get_ports_data())

if __name__ == '__main__':
    app.run(debug=True,host='0.0.0.0')

It works great, but when i run it as a docker container i face a problem with accessing my host to run netstat and get a result. How can i do this?

Answer 1

One of the benefits of Docker is that it isolates a process from the rest of the system, but that also means from inside the container it can be difficult to get information about the host operating system.

I don't know your specific requirements, but my preferred solutions to this in order would be:

1. Don't run this app inside a Docker container at all (its job seems to be gathering information about the host system, so isolating it from the host is counter-productive).

2. Perhaps if you mount /proc/net as a read-only volume inside the container, you can read those files instead of executing netstat . I don't know for sure if this would work and I'd be worried about the security implications, but it could be worth investigating.

3. Run a second service directly on the host which can execute netstat , and have this Flask app communicate with that service.

Answer 2

As stated in the docs , in order to run a command in a running container, you should:

docker exec [OPTIONS] CONTAINER COMMAND [ARG...]

In your case, it should be something like:

docker exec CONTAINER netstat -ltup

If you run

docker exec -it CONTAINER bash

You'll execute an interactive Bash shell on the container. If bash is not available, you can try sh instead.