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I want to get the IP address of a container, I've looked around and chose to add this shell script in my ~/.bashrc:

docker_ip() {
  docker inspect --format '{{ .NetworkSettings.IPAddress }}' "$@"
}

But cuz the containers were connected by custom network, so as below:

"NetworkSettings": {
        "Bridge": "",
        "SandboxID": "e5b42ebd28c5e00e72ab1b7036bf4b1def4036f75ef66994d14a895fd82929bf",
        "HairpinMode": false,
        "LinkLocalIPv6Address": "",
        "LinkLocalIPv6PrefixLen": 0,
        "Ports": {},
        "SandboxKey": "/var/run/docker/netns/e5b42ebd28c5",
        "SecondaryIPAddresses": null,
        "SecondaryIPv6Addresses": null,
        "EndpointID": "",
        "Gateway": "",
        "GlobalIPv6Address": "",
        "GlobalIPv6PrefixLen": 0,
        "IPAddress": "",
        "IPPrefixLen": 0,
        "IPv6Gateway": "",
        "MacAddress": "",
        "Networks": {
            "mynet": {
                "IPAMConfig": null,
                "Links": null,
                "Aliases": [
                    "0819292faeb4"
                ],
                "NetworkID": "4d63adc0879a36550310b50d284718772fe81d01d4ec19a6dc919ad7817c1a3d",
                "EndpointID": "5bfa1bbaa2c446bc5e93d4f14628b8b9e482dd876ae9b89d558fdcc7cf7d0da1",
                "Gateway": "172.18.0.1",
                "IPAddress": "172.18.0.5",
                "IPPrefixLen": 16,
                "IPv6Gateway": "",
                "GlobalIPv6Address": "",
                "GlobalIPv6PrefixLen": 0,
                "MacAddress": "02:42:ac:12:00:05",
                "DriverOpts": null
            }
        }
    }

the IP is not in 

.NetworkSettings.IPAddress

but in : 

.NetworkSettings.Networks.${network_name}.IPAddress

as the ${network_name} is not fixed, I have to modify the shell script in ~/.bashrc to parse the network name, the code in ~/.bashrc is as follow:

function docker_ip(){
    IP=".NetworkSettings.IPAddress" #initialize IP by the default path
    while getopts "n:c:" OPT # n represents custom network name and c represents container ID
    do
         case "$OPT" in
              "n") IP=".NetworkSettings.Networks.${OPTARG}.IPAddress" ;;
              #if n is followed by an argument, it indicates that the network is customized, and thus the default path is replaced.
              "c") containerID=${OPTARG};;
              "?") echo "unrecognized option";;
         esac
    done
    echo"${IP}"
    echo"${containerID}"
    sudo docker inspect --format "{{${IP}}}" ${containerID} #to get the container's IP
}

The main idea of this script is that if the function is called with arguments such as :

$docker_ip -n ${network name} -c containerID

then the script will use .NetworkSettings.Networks.${network_name}.IPAddress to get the IP address. If without argument, such as :

docker_ip -p containerID

which represents that the container is connected by default network, then the script will use .NetworkSettings.IPAddress to get the IP address.

While this does not work properly. When I type $docker_ip -n mynet -c 0819 in the shell prompt the output is supposed to be :

$docker_ip -n mynet -c 0819
.NetworkSettings.Networks.mynet.IPAddress
0819
172.18.0.5

while in fact the output is as follow:

$docker_ip -n mynet -c 0819
.NetworkSettings.IPAddress
0819

As you can see, since the path should be .NetworkSettings.Networks.mynet.IPAddress rather than .NetworkSettings.IPAddress so the IP address of container 0819 cannot be found.

Why this variable cannot change? I am a novice to shell script so I wanted to know if it's right to do so and what would be the best way to do that? Additionally, is there simpler way to get the IP address? Thanks in advance :)

DDelphine
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    Does `docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' $container_id` work? – atline Sep 07 '18 at 09:54
  • @DDelphine I have tried @atline ‘s method, it works well in both cases — with and without user-defined network. And I tried your shell script, it works well too. I swear it. You may try to cut `docker_ip` out as a separated shell script and add `-x` to debug it. – Light.G Sep 07 '18 at 10:27
  • @Light.G The shell script works well for the first time (the output is just what I want) while when I run it for the second time it seems very strange. – DDelphine Sep 07 '18 at 12:17
  • @atline I try your method and it works very well. Thanks very much! – DDelphine Sep 07 '18 at 12:55
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    Possible duplicate: [How to get a Docker container's IP address from the host?](https://stackoverflow.com/q/17157721/596285) – BMitch Sep 07 '18 at 14:18

0 Answers0