How to access host DB from Docker container?

Question

I have PostgreSQL DB running locally and a Docker container with an application that wants to connect there.

How can I access localhost DB from inside docker?

docker run --rm -e "DATABASE_URL=postgresql://postgres:postgres@127.0.0.1:5432/my_db" --network="host" -p 4000:4000 my_image

The above doesn't seem to work. Neither this one: From inside of a Docker container, how do I connect to the localhost of the machine?

Possible duplicate of [From inside of a Docker container, how do I connect to the localhost of the machine?](https://stackoverflow.com/questions/24319662/from-inside-of-a-docker-container-how-do-i-connect-to-the-localhost-of-the-mach) — G07cha, Jun 13 '17 at 14:44
`failed to connect: ** (DBConnection.ConnectionError) tcp connect (127.0.0.1:5432): connection refused - :econnrefused` — Kamil Lelonek, Jun 13 '17 at 17:30
If you execute this command `nc -vz localhost:5432` inside the container, what is the output? -- If you dont have nc command, you can install with apt-get install -y netcat. — German, Jun 13 '17 at 19:06

German · Answer 1 · 2017-06-13T16:15:19.227

0

I think your problem is in param net. In the documentation talk about --network

docker run --rm -e "DATABASE_URL=postgresql://postgres:postgres@127.0.0.1:5432/my_db" --network="host" -p 4000:4000 my_image

edited Jun 13 '17 at 16:15

answered Jun 13 '17 at 14:45

German

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There's no difference actually. – Kamil Lelonek Jun 13 '17 at 18:12
What is the base image you are using? – German Jun 13 '17 at 18:44

score 0 · Answer 2 · answered Jun 13 '17 at 21:01

The settings you have should work correctly, so the problem might be with the configuration of PostgreSQL. The first potential configuration setting I can think of is the bind address. By default this is set to only accept connections from localhost, but since the Docker container will have its own ip address PostgreSQL won't accept traffic from the container. Try setting it to listen_addresses(0.0.0.0) to see if this fixes your problem.

Also be careful to always use 127.0.0.1 as the address because localhost does not always work.

I have currently `listen_addresses = '*'`. – Kamil Lelonek Jun 13 '17 at 22:22 — Kamil Lelonek, Jun 13 '17 at 22:22

gmode · Answer 3 · 2018-10-01T12:39:10.607

I will plagiarize my own answer from here:

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

Sharing host network --net=host:
```
docker run -it --net=host  myimage
```

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:

Edit postgresql.conf to listen on all addresses. By default it will point to localhost.
```
listen_addresses = '*'
```
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.

How to access host DB from Docker container?

3 Answers3