Use ip from env

[shubhamitc]

Extending the support to pull request #544
The Registrator will register services to backend using run-time IPs provided by Kubernetes. Since EKS will use a non-bridge approach i.e. preallocating IPs on Worker-Nodes, we need to have a way to pass dynamic IPs to Registrator.
In Kubernetes, we can use downward status APIs to get POD ips at run time, and we can assign an environment variable to them.

Example:

          - name: POD_IP
            valueFrom:
              fieldRef:
                apiVersion: v1
                fieldPath: status.podIP

With this in mind, we can run registrator like a daemon set, while consul-client is also running as daemonset in Kubernetes.

apiVersion: extensions/v1beta1
kind: DaemonSet
metadata:
  creationTimestamp: null
  labels:
    run: registrator
  name: registrator
spec:
  selector:
    matchLabels:
      run: registrator
  template:
    metadata:
      creationTimestamp: null
      labels:
        run: registrator
        app: registrator
        service: consul-registrator
        department: cloudops
    spec:
      hostNetwork: true
      containers:
      - image: artifactory.arlocloud.com/docker-local/registrator:v4
        name: registrator
        command: ["/bin/sh"]
        args: ["-c", "registrator -useIpFromEnv=POD_IP -explicit=true -resync=60  -cleanup -deregister=always consul://${NODE_IP}:8500"]
        env:
        - name: NODE_NAME
          valueFrom:
            fieldRef:
              fieldPath: spec.nodeName
        - name: NODE_IP
          valueFrom:
            fieldRef:
              fieldPath: status.hostIP
        - name: POD_IP
          valueFrom:
            fieldRef:
              fieldPath: status.podIP
        volumeMounts:
        - mountPath: /tmp/docker.sock
          name: docker-sock
      volumes:
      - name: docker-sock
        hostPath:
          path: /var/run/docker.sock

Now deployment spec can be changed to below to provide auto-registration:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx0-deployment
  labels:
    app: nginx0-deployment
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx0
  template:
    metadata:
      labels:
        app: nginx0
    spec:
      containers:
      - name: nginx
        image: k8s.gcr.io/nginx:1.7.9
        ports:
        - containerPort: 80
        env:
        - name: NODE_NAME
          valueFrom:
            fieldRef:
              fieldPath: spec.nodeName
        - name: NODE_IP
          valueFrom:
            fieldRef:
              fieldPath: status.hostIP
        - name: POD_IP
          valueFrom:
            fieldRef:
              fieldPath: status.podIP
        - name: NAMESPACE
          valueFrom:
            fieldRef:
              fieldPath: metadata.namespace
        - name: SERVICE_80_NAME
          value: nginx
        - name: SERVICE_PORT
          value: "80"
        - name: SERVICE_TAGS
          value: "nginx,eu-west-1"
        resources:
          requests:
            memory: "250Mi"
            cpu: "500m"
          limits:
            memory: "250Mi"
            cpu: "500m"

[shubhamitc]

One valid container spec using docker inspect for validation:

[
    {
        "Id": "4ca22d6d7b1ed00c987285273689fd67a304c59a5ed8678ce8e3ccfd76b12244",
        "Created": "2020-01-10T14:20:04.909668018Z",
        "Path": "nginx",
        "Args": [
            "-g",
            "daemon off;"
        ],
        "State": {
            "Status": "running",
            "Running": true,
            "Paused": false,
            "Restarting": false,
            "OOMKilled": false,
            "Dead": false,
            "Pid": 5050,
            "ExitCode": 0,
            "Error": "",
            "StartedAt": "2020-01-10T14:20:05.108602423Z",
            "FinishedAt": "0001-01-01T00:00:00Z"
        },
        "Image": "sha256:6b60a9253836f5812ef4567776db8bf88f5996f0883bfde6ed6c0ccd02979f08",
        "ResolvConfPath": "/var/lib/docker/containers/85806b20ead4008d9f0a7cd1711ebe22b748820fad372df5e8dee6a1abf9c0f1/resolv.conf",
        "HostnamePath": "/var/lib/docker/containers/85806b20ead4008d9f0a7cd1711ebe22b748820fad372df5e8dee6a1abf9c0f1/hostname",
        "HostsPath": "/var/lib/kubelet/pods/4b5949dd-33b4-11ea-9080-068ce2d35fbe/etc-hosts",
        "LogPath": "/var/lib/docker/containers/4ca22d6d7b1ed00c987285273689fd67a304c59a5ed8678ce8e3ccfd76b12244/4ca22d6d7b1ed00c987285273689fd67a304c59a5ed8678ce8e3ccfd76b12244-json.log",
        "Name": "/k8s_nginx_nginx0-deployment-677bc9b44b-55cvn_consul-client_4b5949dd-33b4-11ea-9080-068ce2d35fbe_0",
        "RestartCount": 0,
        "Driver": "overlay2",
        "Platform": "linux",
        "MountLabel": "",
        "ProcessLabel": "",
        "AppArmorProfile": "",
        "ExecIDs": null,
        "HostConfig": {
            "Binds": [
                "/var/lib/kubelet/pods/4b5949dd-33b4-11ea-9080-068ce2d35fbe/volumes/kubernetes.io~secret/default-token-kcdwp:/var/run/secrets/kubernetes.io/serviceaccount:ro",
                "/var/lib/kubelet/pods/4b5949dd-33b4-11ea-9080-068ce2d35fbe/etc-hosts:/etc/hosts",
                "/var/lib/kubelet/pods/4b5949dd-33b4-11ea-9080-068ce2d35fbe/containers/nginx/5d0e8784:/dev/termination-log"
            ],
            "ContainerIDFile": "",
            "LogConfig": {
                "Type": "json-file",
                "Config": {
                    "max-file": "10",
                    "max-size": "10m"
                }
            },
            "NetworkMode": "container:85806b20ead4008d9f0a7cd1711ebe22b748820fad372df5e8dee6a1abf9c0f1",
            "PortBindings": null,
            "RestartPolicy": {
                "Name": "no",
                "MaximumRetryCount": 0
            },
            "AutoRemove": false,
            "VolumeDriver": "",
            "VolumesFrom": null,
            "CapAdd": null,
            "CapDrop": null,
            "Dns": null,
            "DnsOptions": null,
            "DnsSearch": null,
            "ExtraHosts": null,
            "GroupAdd": null,
            "IpcMode": "container:85806b20ead4008d9f0a7cd1711ebe22b748820fad372df5e8dee6a1abf9c0f1",
            "Cgroup": "",
            "Links": null,
            "OomScoreAdj": -998,
            "PidMode": "",
            "Privileged": false,
            "PublishAllPorts": false,
            "ReadonlyRootfs": false,
            "SecurityOpt": [
                "seccomp=unconfined"
            ],
            "UTSMode": "",
            "UsernsMode": "",
            "ShmSize": 67108864,
            "Runtime": "runc",
            "ConsoleSize": [
                0,
                0
            ],
            "Isolation": "",
            "CpuShares": 512,
            "Memory": 262144000,
            "NanoCpus": 0,
            "CgroupParent": "/kubepods/pod4b5949dd-33b4-11ea-9080-068ce2d35fbe",
            "BlkioWeight": 0,
            "BlkioWeightDevice": null,
            "BlkioDeviceReadBps": null,
            "BlkioDeviceWriteBps": null,
            "BlkioDeviceReadIOps": null,
            "BlkioDeviceWriteIOps": null,
            "CpuPeriod": 100000,
            "CpuQuota": 50000,
            "CpuRealtimePeriod": 0,
            "CpuRealtimeRuntime": 0,
            "CpusetCpus": "",
            "CpusetMems": "",
            "Devices": [],
            "DeviceCgroupRules": null,
            "DiskQuota": 0,
            "KernelMemory": 0,
            "MemoryReservation": 0,
            "MemorySwap": 262144000,
            "MemorySwappiness": null,
            "OomKillDisable": false,
            "PidsLimit": 0,
            "Ulimits": null,
            "CpuCount": 0,
            "CpuPercent": 0,
            "IOMaximumIOps": 0,
            "IOMaximumBandwidth": 0,
            "MaskedPaths": [
                "/proc/acpi",
                "/proc/kcore",
                "/proc/keys",
                "/proc/latency_stats",
                "/proc/timer_list",
                "/proc/timer_stats",
                "/proc/sched_debug",
                "/proc/scsi",
                "/sys/firmware"
            ],
            "ReadonlyPaths": [
                "/proc/asound",
                "/proc/bus",
                "/proc/fs",
                "/proc/irq",
                "/proc/sys",
                "/proc/sysrq-trigger"
            ]
        },
        "GraphDriver": {
            "Data": {
                "LowerDir": "/var/lib/docker/overlay2/8857ff904d0822daa2ec50ebc5aa23fbabfa1fa0f9d644baaec3087debac999d-init/diff:/var/lib/docker/overlay2/9b7eaecedf5fc0f1424e2f33da9c960572df5d310d337666a1566bf4b8ae3b1e/diff:/var/lib/docker/overlay2/455aa47467b133baa5151b7951f023605dad8b6c46a19d024562dc060c9d70e1/diff:/var/lib/docker/overlay2/06d0b5b0585cc96d5f97a87d17af845037cd6541e94ed42b1f0736ac87829df1/diff:/var/lib/docker/overlay2/b1d44cdd08ea0ec08e31c2e8b6a908893ca99288d18638da49193e737b4d30d2/diff:/var/lib/docker/overlay2/b77c69ca1c609f4981a6692863b6d0b6b700c681948814bc27b40f7d08a9278a/diff:/var/lib/docker/overlay2/a872afabaf1c13915442a1d7814500137cc09132a4762fdfd04d3eebb0f16be7/diff:/var/lib/docker/overlay2/63bb79425b96a0ae54ecf4e8b460409f40bd25a53366ae7cc230147c1c5af73c/diff:/var/lib/docker/overlay2/97a4af225e705cb9f90d814f077b48e7280529141eef6ea317fe2cc6c6603abd/diff:/var/lib/docker/overlay2/236fd65f097438cf7a9cc9d229db1275e71748f41c422b6e3fc9c711bea2b3c9/diff:/var/lib/docker/overlay2/53e48c96aa8be9ffd3f7c69b1407cda50e67fdf290d16d04485dffd572c90991/diff:/var/lib/docker/overlay2/6b146c31097f1e009f64f7d8a2288146121fbf6ef7e30d026aa6e859cdcbc329/diff:/var/lib/docker/overlay2/582abe2ad99830bb5e1ce29095ab64c26158e939cfc8972b85ccf23a8ff4aa3a/diff:/var/lib/docker/overlay2/349c452d9f883bffeb5103fff88f3ffda8e2570a253405663e5da2b4fd5c2101/diff",
                "MergedDir": "/var/lib/docker/overlay2/8857ff904d0822daa2ec50ebc5aa23fbabfa1fa0f9d644baaec3087debac999d/merged",
                "UpperDir": "/var/lib/docker/overlay2/8857ff904d0822daa2ec50ebc5aa23fbabfa1fa0f9d644baaec3087debac999d/diff",
                "WorkDir": "/var/lib/docker/overlay2/8857ff904d0822daa2ec50ebc5aa23fbabfa1fa0f9d644baaec3087debac999d/work"
            },
            "Name": "overlay2"
        },
        "Mounts": [
            {
                "Type": "bind",
                "Source": "/var/lib/kubelet/pods/4b5949dd-33b4-11ea-9080-068ce2d35fbe/containers/nginx/5d0e8784",
                "Destination": "/dev/termination-log",
                "Mode": "",
                "RW": true,
                "Propagation": "rprivate"
            },
            {
                "Type": "volume",
                "Name": "ad71247169c4802e2105a694c650db48e6a40e92d4ee0bdfc9a57e78b026bf22",
                "Source": "/var/lib/docker/volumes/ad71247169c4802e2105a694c650db48e6a40e92d4ee0bdfc9a57e78b026bf22/_data",
                "Destination": "/var/cache/nginx",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
            },
            {
                "Type": "bind",
                "Source": "/var/lib/kubelet/pods/4b5949dd-33b4-11ea-9080-068ce2d35fbe/volumes/kubernetes.io~secret/default-token-kcdwp",
                "Destination": "/var/run/secrets/kubernetes.io/serviceaccount",
                "Mode": "ro",
                "RW": false,
                "Propagation": "rprivate"
            },
            {
                "Type": "bind",
                "Source": "/var/lib/kubelet/pods/4b5949dd-33b4-11ea-9080-068ce2d35fbe/etc-hosts",
                "Destination": "/etc/hosts",
                "Mode": "",
                "RW": true,
                "Propagation": "rprivate"
            }
        ],
        "Config": {
            "Hostname": "nginx0-deployment-677bc9b44b-55cvn",
            "Domainname": "",
            "User": "0",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "ExposedPorts": {
                "443/tcp": {},
                "80/tcp": {}
            },
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "POD_IP=172.24.65.84",
                "NAMESPACE=consul-client",
                "SERVICE_80_NAME=nginx",
                "SERVICE_PORT=80",
                "SERVICE_TAGS=nginx,eu-west-1",
                "NODE_NAME=ip-172-24-65-60.eu-west-1.compute.internal",
                "NODE_IP=172.24.65.60",
                "KUBERNETES_SERVICE_PORT=443",
                "KUBERNETES_SERVICE_PORT_HTTPS=443",
                "KUBERNETES_PORT=tcp://10.100.0.1:443",
                "KUBERNETES_PORT_443_TCP=tcp://10.100.0.1:443",
                "KUBERNETES_PORT_443_TCP_PROTO=tcp",
                "KUBERNETES_PORT_443_TCP_PORT=443",
                "KUBERNETES_PORT_443_TCP_ADDR=10.100.0.1",
                "KUBERNETES_SERVICE_HOST=10.100.0.1",
                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                "NGINX_VERSION=1.7.9-1~wheezy"
            ],
            "Cmd": [
                "nginx",
                "-g",
                "daemon off;"
            ],
            "Healthcheck": {
                "Test": [
                    "NONE"
                ]
            },
            "Image": "sha256:6b60a9253836f5812ef4567776db8bf88f5996f0883bfde6ed6c0ccd02979f08",
            "Volumes": {
                "/var/cache/nginx": {}
            },
            "WorkingDir": "",
            "Entrypoint": null,
            "OnBuild": null,
            "Labels": {
                "annotation.io.kubernetes.container.hash": "49d274c8",
                "annotation.io.kubernetes.container.ports": "[{\"containerPort\":80,\"protocol\":\"TCP\"}]",
                "annotation.io.kubernetes.container.restartCount": "0",
                "annotation.io.kubernetes.container.terminationMessagePath": "/dev/termination-log",
                "annotation.io.kubernetes.container.terminationMessagePolicy": "File",
                "annotation.io.kubernetes.pod.terminationGracePeriod": "30",
                "io.kubernetes.container.logpath": "/var/log/pods/consul-client_nginx0-deployment-677bc9b44b-55cvn_4b5949dd-33b4-11ea-9080-068ce2d35fbe/nginx/0.log",
                "io.kubernetes.container.name": "nginx",
                "io.kubernetes.docker.type": "container",
                "io.kubernetes.pod.name": "nginx0-deployment-677bc9b44b-55cvn",
                "io.kubernetes.pod.namespace": "consul-client",
                "io.kubernetes.pod.uid": "4b5949dd-33b4-11ea-9080-068ce2d35fbe",
                "io.kubernetes.sandbox.id": "85806b20ead4008d9f0a7cd1711ebe22b748820fad372df5e8dee6a1abf9c0f1"
            }
        },
        "NetworkSettings": {
            "Bridge": "",
            "SandboxID": "",
            "HairpinMode": false,
            "LinkLocalIPv6Address": "",
            "LinkLocalIPv6PrefixLen": 0,
            "Ports": {},
            "SandboxKey": "",
            "SecondaryIPAddresses": null,
            "SecondaryIPv6Addresses": null,
            "EndpointID": "",
            "Gateway": "",
            "GlobalIPv6Address": "",
            "GlobalIPv6PrefixLen": 0,
            "IPAddress": "",
            "IPPrefixLen": 0,
            "IPv6Gateway": "",
            "MacAddress": "",
            "Networks": {}
        }
    }
]