Access host database from a docker container

There are several long standing discussions about how to do this in a consistent, well understood and portable way. No complete resolution but I'll link you to the discussions below.

In any event you many want to try using the --add-host option to docker run to add the ip address of the host into the container's /etc/host file. From there it's trivial to connect to the host on any required port:

Adding entries to a container hosts file

You can add other hosts into a container's /etc/hosts file by using one or more --add-host flags. This example adds a static address for a host named docker:

 $ docker run --add-host=docker:10.180.0.1 --rm -it debian
    $$ ping docker
    PING docker (10.180.0.1): 48 data bytes
    56 bytes from 10.180.0.1: icmp_seq=0 ttl=254 time=7.600 ms
    56 bytes from 10.180.0.1: icmp_seq=1 ttl=254 time=30.705 ms
    ^C--- docker ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max/stddev = 7.600/19.152/30.705/11.553 ms

Note: Sometimes you need to connect to the Docker host, which means getting the IP address of the host. You can use the following shell commands to simplify this process:

 $ alias hostip="ip route show 0.0.0.0/0 | grep -Eo 'via \S+' | awk '{ print $2 }'"
 $ docker run  --add-host=docker:$(hostip) --rm -it debian

Documentation:

https://docs.docker.com/engine/reference/commandline/run/

Discussions on accessing host from container:

https://github.com/docker/docker/issues/1143

https://github.com/docker/docker/issues/10023

From the 18.03 docs:

I want to connect from a container to a service on the host

The host has a changing IP address (or none if you have no network access). From 18.03 onwards our recommendation is to connect to the special DNS name host.docker.internal, which resolves to the internal IP address used by the host.

The gateway is also reachable as gateway.docker.internal.

EXAMPLE: Here's what I use for my MySQL connection string inside my container to access the MySQL instance on my host:

mysql://host.docker.internal:3306/my_awesome_database

From Docker 17.06 onwards, a special Mac-only DNS name is available in docker containers that resolves to the IP address of the host. It is:

docker.for.mac.localhost

The documentation is here: https://docs.docker.com/docker-for-mac/networking/#httphttps-proxy-support