Access local postgres database from podman container during build

Question

I have a Spring Boot application that runs inside a container and needs to connect to a local Postgresql database. Now it fails at build time, as that is the moment when it tries to configure Spring beans and to connect to database.

I have configured it like following:

spring  
  datasource:
    initialization-mode: always
    platform: postgres
    url: jdbc:postgresql://192.168.122.1:5432/academy
    username: myuser
    password: mypassword

but it fails to connect.

How shall I configure Dockerfile/connection string?

Erik Sjölund · Accepted Answer · 2022-07-24 08:48:43Z

4

I think you have at least two alternatives

Alternative 1: Connecting via Unix domain socket

If you could have Postgres listen on a Unix domain socket, you could then pass in that socket to the container with a bind-mount. Use podman run with one of the command-line arguments --volume or --mount.

Maybe something like:

--mount type=bind,src=/path/to/socket/on/host,target=/path/to/socket/in/container

If your system has SELINUX enabled, you would need to add the option Z

--volume /path/to/socket/on/host:/path/to/socket/in/container:Z

Alternative 2: Connecting via TCP socket

I think you could add the option

--network slirp4netns:allow_host_loopback=true

to the podman run command and connect to the IP address 10.0.2.2.

Quote "Allow the slirp4netns to reach the host loopback IP (10.0.2.2, which is added to /etc/hosts as host.containers.internal for your convenience)" from the podman run man page. See also slirp4netns.1.md.

(The IP address 10.0.2.2 is a default value hard coded in the source code of slirp4netns).

Here is an example of a container that connects to a web server running on localhost:

esjolund@laptop:~$ curl -sS http://localhost:8000/file.txt
hello
esjolund@laptop:~$ cat /etc/issue
Ubuntu 20.04.2 LTS \n \l

esjolund@laptop:~$ podman --version
podman version 3.0.1
esjolund@laptop:~$ podman run --rm docker.io/library/fedora cur-l -sS http://10.0.2.2:8000/file.txt
curl: (7) Failed to connect to 10.0.2.2 port 8000: Network is unreachable
esjolund@laptop:~$ podman run --rm --network slirp4netns:allow_host_loopback=true  docker.io/library/fedora curl -sS http://10.0.2.2:8000/file.txt
hello
esjolund@laptop:~$

edited Jul 24, 2022 at 8:48

answered Mar 16, 2021 at 22:44

Erik Sjölund

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6 Comments

meolic Over a year ago

Where did magic number 10.0.2.2 come from?

Erik Sjölund Over a year ago

Quote "Allow the slirp4netns to reach the host loopback IP (10.0.2.2, which is added to /etc/hosts as host.containers.internal for your convenience)" from podman-run.1.md See also slirp4netns.1.md

Milad Over a year ago

Still doesn't work, on podman version 3.4.2. Host is MacOS.

Milad Over a year ago

Turned out, at least in my case, it was a bug - I have created it and it's going to be fixed in the next 3.4 release, see github.com/containers/podman/issues/12507

Sergio Ocón-Cárdenas Over a year ago

0 VirtualBox: The default address of the virtual DHCP server used in the NAT mode is 10.0.2.2 (this is also the IP address of the default gateway for a VM) The answer assumes that you are using VirtualBox as the virtualization engine.

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