Using the dnsname plugin with Podman

The dnsname plugin allows containers to resolve each other by name. The plugin adds each container's name to an instance of a dnsmasq server. The plugin is enabled through adding it to a network's CNI configuration. The containers will only be able to resolve each other if they are on the same CNI network.

This tutorial assumes you already have Podman, containernetworking-plugins, and a golang development environment installed.

Install dnsmasq

Using your package manager, install the dnsmasq package. For Fedora, this would be: sudo dnf install dnsmasq

AppArmor

If your system uses AppArmor, it can prevent dnsmasq to open the necessary files. To fix this, add the following lines to /etc/apparmor.d/local/usr.sbin.dnsmasq:

# required by the dnsname plugin in podman
/run/containers/cni/dnsname/*/dnsmasq.conf r,
/run/containers/cni/dnsname/*/addnhosts r,
/run/containers/cni/dnsname/*/pidfile rw,

Then reload the main dnsmasq profile:

sudo apparmor_parser -r /etc/apparmor.d/usr.sbin.dnsmasq

Build and install

1. using git, clone the github.com/containers/dnsname repository.
2. make install PREFIX=/usr -- this will install the dnsname plugin into /usr/libexec/cni where your CNI plugins should already exist.

Configure a CNI network for Podman

1. Create a new network using podman network create. For example, podman network create foobar will suffice.

The following example configuration file shows a usable example for Podman.

2. (optional)+The configuration will be automatically enabled for newly created networks via podman network create. If you want to add this feature to an exisiting network add the needed lines to /etc/cni/net.d/foobar.conflist using your favorite editor. For example:

{
  "cniVersion": "0.4.0",
  "name": "foobar",
  "plugins": [
     ...
     {
        "type": "dnsname",
        "domainName": "dns.podman",
        "capabilities": {
           "aliases": true
        }
     }
  ]
}

Example: container name resolution

In this test image, the nginx server will respond with podman rulez on an http request. Note: we use the --network foobar here.

sudo podman run -dt --name web --network foobar quay.io/libpod/alpine_nginx:latest
5139d65d22135e9ecab511559d863754550894a32285befd94dab231017048c2

sudo podman run -it --name client --network foobar quay.io/libpod/alpine_nginx:latest curl http://web.dns.podman/
podman rulez

Enabling name resolution on the default Podman network

After making sure the dnsplugin is functioning properly, you can add name resolution to your default Podman network. This can be done two different ways:

1. Add the dnsname plugin as described in above to your default Podman network. This default network is usually /etc/cni/net.d/87-podman-bridge.conflist.