Tuesday, July 11, 2017

Oracle Linux - finding your docker container IP

In our examples we are running a Docker engine on an Oracle Linux host which we use to explain how you can work with Docker and containers. In this example post we have a single Oracle NoSQL container running on our docker engine. When a Docker containers is started in a default manner it will get an internal IP which is accessible within docker by other containers. As part of your deployment model and scripting it is very well likely that you want to know the IP address assigned to a newly started conatiner without the need to go into the container. The need to get this information directly is a very likely scenario. To get more information from a host you can use the inspect command as part of the docker CLI. The inspect command provides you a JSON response containing a large set of information about a specific container.

The inspect command is used in combination with the container ID. This means we first have to get the container ID, one way of getting the container ID is using the "docker ps" command as shown below:

[root@localhost etc]# docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                          NAMES
0a52831c65e8        oracle/nosql        "java -jar lib/kvstor"   11 hours ago        Up 11 hours         5000-5001/tcp, 5010-5020/tcp   nosql_node_0
[root@localhost etc]# 

If we want to know more about the container running, and identified with container ID 0a52831c65e8 wen can execute the "docker inspect" command to retrieve the JSON response as shown in the example below:

[root@localhost etc]# docker inspect 0a52831c65e8
[
    {
        "Id": "0a52831c65e86727b248bc66c2cb5e4be037f85473a6c0645f8b81c5f2381e4f",
        "Created": "2017-07-10T19:43:49.205922395Z",
        "Path": "java",
        "Args": [
            "-jar",
            "lib/kvstore.jar",
            "kvlite",
            "-secure-config",
            "disable",
            "-root",
            "/kvroot"
        ],
        "State": {
            "Status": "running",
            "Running": true,
            "Paused": false,
            "Restarting": false,
            "OOMKilled": false,
            "Dead": false,
            "Pid": 5364,
            "ExitCode": 0,
            "Error": "",
            "StartedAt": "2017-07-10T19:43:49.636183576Z",
            "FinishedAt": "0001-01-01T00:00:00Z"
        },
        "Image": "sha256:247be918b211e6690ad33463336e502c260b1a35010102d93967bd49dc061e46",
        "ResolvConfPath": "/var/lib/docker/containers/0a52831c65e86727b248bc66c2cb5e4be037f85473a6c0645f8b81c5f2381e4f/resolv.conf",
        "HostnamePath": "/var/lib/docker/containers/0a52831c65e86727b248bc66c2cb5e4be037f85473a6c0645f8b81c5f2381e4f/hostname",
        "HostsPath": "/var/lib/docker/containers/0a52831c65e86727b248bc66c2cb5e4be037f85473a6c0645f8b81c5f2381e4f/hosts",
        "LogPath": "/var/lib/docker/containers/0a52831c65e86727b248bc66c2cb5e4be037f85473a6c0645f8b81c5f2381e4f/0a52831c65e86727b248bc66c2cb5e4be037f85473a6c0645f8b81c5f2381e4f-json.log",
        "Name": "/nosql_node_0",
        "RestartCount": 0,
        "Driver": "devicemapper",
        "MountLabel": "",
        "ProcessLabel": "",
        "AppArmorProfile": "",
        "ExecIDs": null,
        "HostConfig": {
            "Binds": null,
            "ContainerIDFile": "",
            "LogConfig": {
                "Type": "json-file",
                "Config": {}
            },
            "NetworkMode": "default",
            "PortBindings": {},
            "RestartPolicy": {
                "Name": "no",
                "MaximumRetryCount": 0
            },
            "AutoRemove": false,
            "VolumeDriver": "",
            "VolumesFrom": null,
            "CapAdd": null,
            "CapDrop": null,
            "Dns": [],
            "DnsOptions": [],
            "DnsSearch": [],
            "ExtraHosts": null,
            "GroupAdd": null,
            "IpcMode": "",
            "Cgroup": "",
            "Links": null,
            "OomScoreAdj": 0,
            "PidMode": "",
            "Privileged": false,
            "PublishAllPorts": false,
            "ReadonlyRootfs": false,
            "SecurityOpt": null,
            "UTSMode": "",
            "UsernsMode": "",
            "ShmSize": 67108864,
            "Runtime": "runc",
            "ConsoleSize": [
                0,
                0
            ],
            "Isolation": "",
            "CpuShares": 0,
            "Memory": 0,
            "CgroupParent": "",
            "BlkioWeight": 0,
            "BlkioWeightDevice": null,
            "BlkioDeviceReadBps": null,
            "BlkioDeviceWriteBps": null,
            "BlkioDeviceReadIOps": null,
            "BlkioDeviceWriteIOps": null,
            "CpuPeriod": 0,
            "CpuQuota": 0,
            "CpusetCpus": "",
            "CpusetMems": "",
            "Devices": [],
            "DiskQuota": 0,
            "KernelMemory": 0,
            "MemoryReservation": 0,
            "MemorySwap": 0,
            "MemorySwappiness": -1,
            "OomKillDisable": false,
            "PidsLimit": 0,
            "Ulimits": null,
            "CpuCount": 0,
            "CpuPercent": 0,
            "IOMaximumIOps": 0,
            "IOMaximumBandwidth": 0
        },
        "GraphDriver": {
            "Name": "devicemapper",
            "Data": {
                "DeviceId": "34",
                "DeviceName": "docker-251:1-1835143-986c026ad2d7e69cae96df9d46f1d15c23c88103f7dc7d7756a8be2f50f474ea",
                "DeviceSize": "10737418240"
            }
        },
        "Mounts": [
            {
                "Name": "a37d7c33e0d78922160c4b411f13350e9692dddf26cdea794a5dd6f266723175",
                "Source": "/var/lib/docker/volumes/a37d7c33e0d78922160c4b411f13350e9692dddf26cdea794a5dd6f266723175/_data",
                "Destination": "/kvroot",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
            }
        ],
        "Config": {
            "Hostname": "0a52831c65e8",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "ExposedPorts": {
                "5000/tcp": {},
                "5001/tcp": {},
                "5010/tcp": {},
                "5011/tcp": {},
                "5012/tcp": {},
                "5013/tcp": {},
                "5014/tcp": {},
                "5015/tcp": {},
                "5016/tcp": {},
                "5017/tcp": {},
                "5018/tcp": {},
                "5019/tcp": {},
                "5020/tcp": {}
            },
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                "JAVA_HOME=/usr/lib/jvm/java-openjdk",
                "VERSION=4.3.11",
                "KVHOME=/kv-4.3.11",
                "PACKAGE=kv-ce",
                "EXTENSION=zip",
                "BASE_URL=http://download.oracle.com/otn-pub/otn_software/nosql-database/",
                "_JAVA_OPTIONS=-Djava.security.egd=file:/dev/./urandom"
            ],
            "Cmd": [
                "java",
                "-jar",
                "lib/kvstore.jar",
                "kvlite",
                "-secure-config",
                "disable",
                "-root",
                "/kvroot"
            ],
            "Image": "oracle/nosql",
            "Volumes": {
                "/kvroot": {}
            },
            "WorkingDir": "/kv-4.3.11",
            "Entrypoint": null,
            "OnBuild": null,
            "Labels": {}
        },
        "NetworkSettings": {
            "Bridge": "",
            "SandboxID": "3f3505304a821da97a668ae622a09738cf8c88768e77f5c1995154f431461700",
            "HairpinMode": false,
            "LinkLocalIPv6Address": "",
            "LinkLocalIPv6PrefixLen": 0,
            "Ports": {
                "5000/tcp": null,
                "5001/tcp": null,
                "5010/tcp": null,
                "5011/tcp": null,
                "5012/tcp": null,
                "5013/tcp": null,
                "5014/tcp": null,
                "5015/tcp": null,
                "5016/tcp": null,
                "5017/tcp": null,
                "5018/tcp": null,
                "5019/tcp": null,
                "5020/tcp": null
            },
            "SandboxKey": "/var/run/docker/netns/3f3505304a82",
            "SecondaryIPAddresses": null,
            "SecondaryIPv6Addresses": null,
            "EndpointID": "28368b7c9058e300d08cc3a3453568cb903504ed33b4c61c6349963ad190160f",
            "Gateway": "172.17.0.1",
            "GlobalIPv6Address": "",
            "GlobalIPv6PrefixLen": 0,
            "IPAddress": "172.17.0.2",
            "IPPrefixLen": 16,
            "IPv6Gateway": "",
            "MacAddress": "02:42:ac:11:00:02",
            "Networks": {
                "bridge": {
                    "IPAMConfig": null,
                    "Links": null,
                    "Aliases": null,
                    "NetworkID": "fc7e96b764adee7ae2a6f061b766c61ea82ec7754faa64f2483889fa0a5a3a5f",
                    "EndpointID": "28368b7c9058e300d08cc3a3453568cb903504ed33b4c61c6349963ad190160f",
                    "Gateway": "172.17.0.1",
                    "IPAddress": "172.17.0.2",
                    "IPPrefixLen": 16,
                    "IPv6Gateway": "",
                    "GlobalIPv6Address": "",
                    "GlobalIPv6PrefixLen": 0,
                    "MacAddress": "02:42:ac:11:00:02"
                }
            }
        }
    }
]
[root@localhost etc]#

As you can see above the "docker inspect" command provides a very rich set of information whcih can be used for a variaty of things. However, in our example case we only wanted to know the IP address which has been assigned to the container. This means we will have to extract the IP from the JSON response. The below comman will help you in extracting just that from the larger set of information:

[root@localhost etc]# docker inspect 0a52831c65e8 | grep IPAddress | cut -d '"' -f 4| sort -r | head -1
172.17.0.2
[root@localhost etc]#

The above example could be the starting point of a bash function in a wider script which allows you to simply call a function in combination with a variable for the container ID and return the IP information you need. Knowing and understanding how to quickly extract the IP information from the inspect command can help you in building scripting arround docker.
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