Allow Podman containers to resolve each other by container name on an Oracle Compute Instance

Allow Podman containers to resolve each other by container name on an Oracle Compute Instance

Matt Mulvaney's photo
Matt Mulvaney
·

3 min read

This was driving me potty. Although I have finally found a solution by using the dnsname CNI plugin for Podman.

First, let's confirm we have a problem on our box, by creating a new network and 2 test containers, to see if they can communicate with each other

docker network create mynetwork
podman run -d --name node0 --network mynetwork docker.io/alpine:latest sleep inf
podman run -d --name node1 --network mynetwork docker.io/alpine:latest sleep inf
podman exec -it node0 ping -c2 node1

A successful result would be

PING node1 (10.89.0.17): 56 data bytes
64 bytes from 10.89.0.17: seq=0 ttl=64 time=0.159 ms
64 bytes from 10.89.0.17: seq=1 ttl=64 time=0.069 ms

--- node1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.069/0.114/0.159 ms

However, if the result is...

ping: bad address 'node1'

...then we need to follow these steps to fix this & all future networks.

  1. Install the following tools

     sudo dnf install git -y
 sudo dnf install golang -y
 sudo dnf install dnsmasq -y
 sudo dnf install nano -y

  2. Clone the dnsname repository:

     git clone https://github.com/containers/dnsname.git

  3. Build the plugin using golang

     cd dnsname
 make

  4. Copy the plugin into the directory with the other CNI plugins:

     sudo cp bin/dnsname /usr/libexec/cni

  5. Add support for dnsname to one or more Podman networks. All networks will appear in /home/opc/.config/cni/net.d so in this example, we will edit the mynetwork network

     nano /home/opc/.config/cni/net.d/mynetwork.conflist

  6. Paste the following

      {
     "type": "dnsname",
     "domainName": "dns.podman",
     "capabilities": {
        "aliases": true
     }
  },

    at a new line directly after "plugins": [ so that it looks like this at the top of the file.

     {
    "cniVersion": "0.4.0",
    "name": "mynetwork",
    "plugins": [
  {
     "type": "dnsname",
     "domainName": "dns.podman",
     "capabilities": {
        "aliases": true
     }
  },
       {
          "type": "bridge",
          "bridge": "cni-podman1",
          "isGateway": true,
          "ipMasq": true,

  7. CTRL+X to save the file & exit the editor

  8. Remove the containers & retest

     # Remove
 podman stop node0
 podman stop node1
 podman rm node0
 podman rm node1
 podman network rm mynetwork
 # create
 docker network create mynetwork
 podman run -d --name node0 --network mynetwork docker.io/alpine:latest sleep inf
 podman run -d --name node1 --network mynetwork docker.io/alpine:latest sleep inf
 podman exec -it node0 ping -c2 node1

  9. If this works, we should see a ping success

     PING node1 (10.89.0.17): 56 data bytes
 64 bytes from 10.89.0.17: seq=0 ttl=64 time=0.159 ms
 64 bytes from 10.89.0.17: seq=1 ttl=64 time=0.069 ms

 --- node1 ping statistics ---
 2 packets transmitted, 2 packets received, 0% packet loss
 round-trip min/avg/max = 0.069/0.114/0.159 ms

  10. Tidy up the test by removing the test containers

    # Remove
podman stop node0
podman stop node1
podman rm node0
podman rm node1
podman network rm mynetwork

  11. BONUS FEATURE: Once the dnsname plugin is installed, it will be enabled by default on all new networks. I.e after installing dnsname, all new networks on my Compute box had the plugin enabled

  12. ENJOY

Credits to Larsks for this post. I adapted his solution to Oracle Compute Unix.

What's the picture? It's Brothers Water in Cumbria. Visit Cumbria ... and Yorkshire too.

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