[docker] Access host database from a docker container

If I have a mysql database running on some host machine, and that host is also running a docker container: How would I access the mysql database from within the docker container that is running on the host?.

For instance, is there a way to publish a hosts port to the container (the inverse of what docker run -p does)?

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

If you want access to a Docker container where there is a DB, you have to add a bash:

docker exec -it postgresql bash

postgresql is the container name.

Once inside, from the bash, access to DB e.g:

$psql -U postgres

Other answers did not work well for me. My container could not resolve host ip using host.docker.internal. There are two ways

1. Sharing host network --net=host:

   docker run -it --net=host  myimage
   

2. Using docker's ip address, which is usually 172.17.0.1. You can check it by calling ifconfig command and grabbing inet addr of docker interface

   user@ubuntu:~$ ifconfig
   docker0   Link encap:Ethernet  HWaddr 02:42:a4:a2:b2:f1  
     inet addr:172.17.0.1  Bcast:0.0.0.0  Mask:255.255.0.0
     inet6 addr: fe80::42:a4ff:fea2:b2f1/64 Scope:Link
   

Once you have this ip address, you can pass it as an argument to docker run and then to application or as I do it, map the location of jdbc.properties via volume to the directory on host machine, so you can manage the file externally.

  docker run -it -v /host_dir/docker_jdbc_config:${jetty_base}/var/config myimage

NOTE: Your database might not allow external connections. In case of postgresql, you need to edit 2 files, as described here and here:

1. Edit postgresql.conf to listen on all addresses. By default it will point to localhost.

   listen_addresses = '*'
   

2. Edit pg_hba.conf to allow connections from all addresses. Add on the last line:

   host     all             all             0.0.0.0/0               md5
   

IMPORTANT: Last step updating database access is not recommended for production use unless you are really sure what you are doing.

Use host.docker.internal from Docker 18.03 onwards.

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