I'm trying to get two containers to talk via host name. However, the host names don't seem to resolve. They can ping each other happily via IP. I'm using a user created network which I understand is required for automatic host name resolution.

I haven't used Podman before. Is there some additional setup required for container name resolution?

Simplified docker-compose.yml which demonstrates the issue

---
version: "3"

services:
  app1:
    image: docker.io/wbitt/network-multitool:latest
    container_name: app1
    networks:
      - internal-network

  app2:
    image: docker.io/wbitt/network-multitool:latest
    container_name: app2
    networks:
      - internal-network

networks:
  internal-network:
    driver: bridge

Inspecting each container does show that they are connected to the user defined network.

App1

"Networks": {
    "network-issue_internal-network": {
        "IPAMConfig": null,
        "Links": null,
        "Aliases": [
            "4d2425e5c3e5",
            "app1"
        ],
        "NetworkID": "network-issue_internal-network",
        "EndpointID": "",
        "Gateway": "10.88.4.1",
        "IPAddress": "10.88.4.27",
        "IPPrefixLen": 24,
        "IPv6Gateway": "",
        "GlobalIPv6Address": "",
        "GlobalIPv6PrefixLen": 0,
        "MacAddress": "86:d1:52:53:84:b3",
        "DriverOpts": null
    }
}

App2

"Networks": {
    "network-issue_internal-network": {
        "IPAMConfig": null,
        "Links": null,
        "Aliases": [
            "3f6ed535b139",
            "app2"
        ],
        "NetworkID": "network-issue_internal-network",
        "EndpointID": "",
        "Gateway": "10.88.4.1",
        "IPAddress": "10.88.4.26",
        "IPPrefixLen": 24,
        "IPv6Gateway": "",
        "GlobalIPv6Address": "",
        "GlobalIPv6PrefixLen": 0,
        "MacAddress": "fe:1f:cf:e7:80:52",
        "DriverOpts": null
    }
}

Oddly, when I inspect the user defined network it doesn't list any containers.

[
    {
        "args": {
            "podman_labels": {
                "com.docker.compose.network": "internal-network",
                "com.docker.compose.project": "network-issue",
                "com.docker.compose.version": "1.25.0"
            }
        },
        "cniVersion": "0.4.0",
        "name": "network-issue_internal-network",
        "plugins": [
            {
                "bridge": "cni-podman2",
                "hairpinMode": true,
                "ipMasq": true,
                "ipam": {
                    "ranges": [
                        [
                            {
                                "gateway": "10.88.4.1",
                                "subnet": "10.88.4.0/24"
                            }
                        ]
                    ],
                    "routes": [
                        {
                            "dst": "0.0.0.0/0"
                        }
                    ],
                    "type": "host-local"
                },
                "isGateway": true,
                "type": "bridge"
            },
            {
                "capabilities": {
                    "portMappings": true
                },
                "type": "portmap"
            },
            {
                "backend": "",
                "type": "firewall"
            },
            {
                "type": "tuning"
            }
        ]
    }
]

Dig output from app2 looking up app1

# dig app1

; <<>> DiG 9.16.22 <<>> app1
;; global options:  cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 3565
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1280
;; QUESTION SECTION:
;app1.                          IN      A

;; AUTHORITY SECTION:
.                       1356    IN      SOA     a.root-servers.net. nstld.verisign-grs.com. 2022100302 1800 900 604800 86400

;; Query time: 0 msec
;; SERVER: 192.168.1.1#53(192.168.1.1)
;; WHEN: Tue Oct 04 00:12:49 UTC 2022
;; MSG SIZE  rcvd: 108

Other details

• Distro: Raspbian GNU/Linux 11
• Podman Version: 3.0.1

CodePudding user response：

It looks like the Podman package on Raspbian 11 does not ship with the dnsname plugin. It's relatively easy to install.

1. Clone the repository:

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

2. Build the plugin. You'll need to install the golang package first:

   sudo apt -y install golang
   

   And then:

   cd dnsname
   make
   

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

   sudo cp bin/dnsname /usr/lib/cni/
   

4. Add support for dnsname to one or more podman networks. That means adding a stanza like this to the plugins list of the appropriate file under /etc/cni/net.d:

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

With these changes in place, I can successfully start up two containers on a user-defined network and have them communicate by name:

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

Running the above commands (as root) produces:

PING node1 (10.88.2.4): 56 data bytes
64 bytes from 10.88.2.4: seq=0 ttl=42 time=0.308 ms
64 bytes from 10.88.2.4: seq=1 ttl=42 time=0.543 ms

--- node1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.308/0.425/0.543 ms