How do I access the specific method of the native of host in Docker

Question

Docker needs to access the native database, how to access. Using 127.0.0.1 is definitely not possible, as this refers to the container itself within the Docker container. Therefore, the need to move the channel to solve.

Solution

The following methods, according to the type of operating system, select its 1.

DockerFile:

RUN /sbin/ip route|awk '/default/ { print $3,"\tdockerhost" }' >> /etc/hosts

RunTime:

(may not use) docker run --add-host dockerhost:`/sbin/ip route|awk '/default/ { print $3}'` [my container]
(useful) docker run --add-host=dockerhost:`docker network inspect --format='{{range .IPAM.Config}}{{.Gateway}}{{end}}' bridge` [IMAGE]

Docker for Mac (17.12+):

docker.for.mac.host.internal
MONGO_SERVER=docker.for.mac.host.internal

# docker-compose.yml
version: '3'

services:
 api:
  build: ./api
  volumes:
   - ./api:/usr/src/app:ro
  ports:
   - "8000"
  environment:
   - MONGO_SERVER
  command: /usr/local/bin/gunicorn -c /usr/src/app/gunicorn_config.py -w 1 -b :8000 wsgi

Linux

 #  Solution 1
/sbin/ip route|awk '/default/ { print $3 }'
docker run --add-host dockerhost:`/sbin/ip route|awk '/default/ { print $3}'` [my container]
 #  Solution 2
-e "DOCKER_HOST=$(ip -4 addr show docker0 | grep -Po 'inet \K[\d.]+')"

Principle

To understand the principle, you need to understand the model of the computer network and the model of the docker implementation. docker internal docker0 actually realizes a virtual Bridges, need to find outside of the host machine through the bridge in the virtual address of the bridge, namely docker. for. mac. host. internal, container can access external host machine. If you are interested, you can learn about Docker's network principle, computer network principle and docker compose, etc.

Reference

[1].(stackoverflow)insert-docker-parent-host-ip-into-containers-hosts-file

[2].(stackoverflow)how-to-get-the-ip-address-of-the-docker-host-from-inside-a-docker-container