devilbox/docs/advanced/connect-to-host-os.rst

Connect to host OS

This section explains how to connect from inside a Devilbox container to the host operating system.

Table of Contents

local

Prerequisites

When you want to connect from inside a Docker container to a port on your host operating system, ensure the host service is listening on all interfaces for simplicity.

The following sections will give you the IP address and/or the CNAME where the host os can be reached from within a container.

Docker on Linux

If you run Docker on Linux the host IP is always 172.16.238.1, which is the default gateway IP address within the Devilbox bridge network (see docker-compose.yml).

Important

Ensure services on the host listen on that IP address or on all interfaces.

By default Docker on Linux does not have CNAME's of the host computer as for example with MacOS or Windows, therefore two custom CNAME's have been added by the Devilbox in order to emulate the same behaviour:

• CNAME: docker.for.lin.host.internal
• CNAME: docker.for.lin.localhost

Docker for Mac

If you run Docker for Mac, an IP address is not necessary as it already provides a CNAME which will always point to the IP address of your host operating system. Depending on the Docker version this CNAME will differ:

Docker 18.03.0-ce+ and Docker compose 1.20.1+

CNAME: host.docker.internal

Docker 17.12.0-ce+ and Docker compose 1.18.0+

CNAME: docker.for.mac.host.internal

Docker 17.06.0-ce+ and Docker compose 1.14.0+

CNAME: docker.for.mac.localhost

Docker for Windows

If you run Docker for Windows, an IP address is not necessary as it already provides a CNAME which will always point to the IP address of your host operating system. Depending on the Docker version this CNAME will differ:

Important

Ensure your firewall is not blocking Docker to host connections.

Docker 18.03.0-ce+ and Docker compose 1.20.1+

• CNAME: docker.for.win.host.internal
• CNAME: host.docker.internal

Docker 17.06.0-ce+ and Docker compose 1.14.0+

CNAME: docker.for.win.host.localhost

Docker Toolbox

Note

This section applies for both, Docker Toolbox on MacOS and Docker Toolbox on Windows.

Docker Toolbox behaves the same way as Docker on Linux, with one major difference. The Devilbox IP address or the custom provided CNAMEs actually refer to the Docker Toolbox machine.

In order to connect from inside the Docker container (which is inside the Docker Toolbox machine) to your host os, you need to create:

1. either a local port-forward on the Docker Toolbox machine (ssh -L)
2. or a remote port-forward on your host os (ssh -R)

For both examples we assume the following:

• MySQL database exists on your host os and listens on 127.0.0.1 on port 3306
• Docker Toolbox IP address is 192.168.99.100
• Host IP address where SSH is listening on 172.16.0.1
• Host SSH username is user
• Devilbox Docker container wants to access MySQL on host os

Local port forward on Docker Toolbox

Important

For that to work, your host operating system requires an SSH server to be up and running.

Initiator	From host	From port	To host	To port
Docker Toolbox	127.0.0.1	3306	192.168.99.100	3306

# From Docker Toolbox forward port 3306 (on host 172.16.0.1) to myself (192.168.99.100)
toolbox> ssh -L 3306:127.0.0.1:3306 user@172.16.0.1

* howto_find_docker_toolbox_ip_address * howto_ssh_into_docker_toolbox * howto_ssh_port_forward_on_docker_toolbox_from_host

Remote port-forward on host os

Important

For that to work, your host operating system requires an SSH client (ssh binary).

Initiator	From host	From port	To host	To port
Host os	127.0.0.1	3306	192.168.99.100	3306

# From host os forward port 3306 (from loopback 127.0.0.1) to Docker Toolbox (192.168.99.100)
host> ssh -R 3306:127.0.0.1:3306 docker@192.168.99.100

* howto_find_docker_toolbox_ip_address * howto_ssh_into_docker_toolbox * howto_ssh_port_forward_on_host_to_docker_toolbox

Post steps

With either of the above you have achieved the exact behaviour as connect_to_host_os_docker_on_linux for one single service/port (MySQL port 3306).

You must now follow the steps for connect_to_host_os_docker_on_linux to actually connect to that service from within the Devilbox Docker container.