Getting the name of the container from within the container - docker

Question

I would like to get the docker container name from within a container. I need this information because I am running a script from the Dockerfile as an ENTRYPOINT that needs to know the node number. I am using the --scale with docker-compose to create a cluster of my image.
I am able to get the hostname of the container which is the container ID. But is there a way to get the container name from inside the container?

Answer 1

Docker remote apis should work for you.
Depending on the version of your docker used appropriate version of remote api. Check this for more info.
I made use of container-inspect api to retrieve the container name.
Follow these steps:
Figure out on which port docker daemon is listening. In my case it was 2375 which is the default port.
$ netstat -anp | grep dockerd
tcp 0 0 :::2375 :::* LISTEN 7/dockerd
tcp 0 0 ::ffff:172.18.0.110:2375 ::ffff:172.18.0.1:29445 ESTABLISHED 7/dockerd
unix 2 [ ACC ] STREAM LISTENING 1242188041 7/dockerd /var/run/docker/metrics.sock
unix 2 [ ACC ] STREAM LISTENING 1242187193 7/dockerd /var/run/docker.sock
unix 2 [ ACC ] STREAM LISTENING 1242186375 7/dockerd /var/run/docker/libnetwork/79ba9bb412445c757dd4cc2fc30c1cbc7efde8482bdc4c1cf15c4ce0e4190752.sock
unix 3 [ ] STREAM CONNECTED 1242187211 7/dockerd
unix 3 [ ] STREAM CONNECTED 1242183625 7/dockerd
unix 3 [ ] STREAM CONNECTED 1242184185 7/dockerd
Run a container and retrieve the container name.
$ docker run -it alpine sh
/ # apk update
/ # apk add curl
/ # apk add jq
/ # curl -s 192.168.0.37:2375/containers/$HOSTNAME/json | jq -r ".Name"
/zen_wescoff
NOTE: Here 192.168.0.37 is the ip of my machine. Also apart from container name you can retrieve lot of information using these docker remote apis.
Sample full output of container-inspect api
/ # curl -s 192.168.0.37:2375/containers/$HOSTNAME/json?pretty=true
{
"Id": "3409974f45bedacd3adbe663679e4eb7a74006483e3a3b04985e5a7cc65229b9",
"Created": "2019-06-20T09:09:51.258807808Z",
"Path": "sh",
"Args": [],
"State": {
"Status": "running",
"Running": true,
"Paused": false,
"Restarting": false,
"OOMKilled": false,
"Dead": false,
"Pid": 3824,
"ExitCode": 0,
"Error": "",
"StartedAt": "2019-06-20T09:09:53.341188978Z",
"FinishedAt": "0001-01-01T00:00:00Z"
},
"Image": "sha256:4d90542f0623c71f1f9c11be3da23167174ac9d93731cf91912922e916bab02c",
"ResolvConfPath": "/var/lib/docker/containers/3409974f45bedacd3adbe663679e4eb7a74006483e3a3b04985e5a7cc65229b9/resolv.conf",
"HostnamePath": "/var/lib/docker/containers/3409974f45bedacd3adbe663679e4eb7a74006483e3a3b04985e5a7cc65229b9/hostname",
"HostsPath": "/var/lib/docker/containers/3409974f45bedacd3adbe663679e4eb7a74006483e3a3b04985e5a7cc65229b9/hosts",
"LogPath": "/var/lib/docker/containers/3409974f45bedacd3adbe663679e4eb7a74006483e3a3b04985e5a7cc65229b9/3409974f45bedacd3adbe663679e4eb7a74006483e3a3b04985e5a7cc65229b9-json.log",
"Name": "/jovial_moser",
"RestartCount": 0,
"Driver": "overlay2",
"Platform": "linux",
"MountLabel": "",
"ProcessLabel": "",
"AppArmorProfile": "docker-default",
"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,
"Capabilities": null,
"Dns": [],
"DnsOptions": [],
"DnsSearch": [],
"ExtraHosts": null,
"GroupAdd": null,
"IpcMode": "private",
"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,
"NanoCpus": 0,
"CgroupParent": "",
"BlkioWeight": 0,
"BlkioWeightDevice": [],
"BlkioDeviceReadBps": null,
"BlkioDeviceWriteBps": null,
"BlkioDeviceReadIOps": null,
"BlkioDeviceWriteIOps": null,
"CpuPeriod": 0,
"CpuQuota": 0,
"CpuRealtimePeriod": 0,
"CpuRealtimeRuntime": 0,
"CpusetCpus": "",
"CpusetMems": "",
"Devices": [],
"DeviceCgroupRules": null,
"DeviceRequests": null,
"DiskQuota": 0,
"KernelMemory": 0,
"KernelMemoryTCP": 0,
"MemoryReservation": 0,
"MemorySwap": 0,
"MemorySwappiness": null,
"OomKillDisable": false,
"PidsLimit": null,
"Ulimits": null,
"CpuCount": 0,
"CpuPercent": 0,
"IOMaximumIOps": 0,
"IOMaximumBandwidth": 0,
"MaskedPaths": ["/proc/asound", "/proc/acpi", "/proc/kcore", "/proc/keys", "/proc/latency_stats", "/proc/timer_list", "/proc/timer_stats", "/proc/sched_debug", "/proc/scsi", "/sys/firmware"],
"ReadonlyPaths": ["/proc/bus", "/proc/fs", "/proc/irq", "/proc/sys", "/proc/sysrq-trigger"]
},
"GraphDriver": {
"Data": {
"LowerDir": "/var/lib/docker/overlay2/a5f16849169cb7c773f4d204089f8e53daf5b648864846ee1d1f076cef9f8a39-init/diff:/var/lib/docker/overlay2/edb63c15d70f0a29c60f3725ed952dd76439bef4da8915e66ffe6ed1ecf02107/diff",
"MergedDir": "/var/lib/docker/overlay2/a5f16849169cb7c773f4d204089f8e53daf5b648864846ee1d1f076cef9f8a39/merged",
"UpperDir": "/var/lib/docker/overlay2/a5f16849169cb7c773f4d204089f8e53daf5b648864846ee1d1f076cef9f8a39/diff",
"WorkDir": "/var/lib/docker/overlay2/a5f16849169cb7c773f4d204089f8e53daf5b648864846ee1d1f076cef9f8a39/work"
},
"Name": "overlay2"
},
"Mounts": [],
"Config": {
"Hostname": "3409974f45be",
"Domainname": "",
"User": "",
"AttachStdin": true,
"AttachStdout": true,
"AttachStderr": true,
"Tty": true,
"OpenStdin": true,
"StdinOnce": true,
"Env": ["PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"],
"Cmd": ["sh"],
"Image": "alpine",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": null,
"OnBuild": null,
"Labels": {}
},
"NetworkSettings": {
"Bridge": "",
"SandboxID": "7f41a5043e99bb110e215ac8e13a8a2c37838b25c6a9fa985584ff458c1e52cc",
"HairpinMode": false,
"LinkLocalIPv6Address": "",
"LinkLocalIPv6PrefixLen": 0,
"Ports": {},
"SandboxKey": "/var/run/docker/netns/7f41a5043e99",
"SecondaryIPAddresses": null,
"SecondaryIPv6Addresses": null,
"EndpointID": "7aa9f269772edff8a9b7f895d51d6dd472a5820ff56a643134465ab8bff1914e",
"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": "55987078c24843c830172de5c352b00c96cb3f177a349437dd7bee9bd1814e86",
"EndpointID": "7aa9f269772edff8a9b7f895d51d6dd472a5820ff56a643134465ab8bff1914e",
"Gateway": "172.17.0.1",
"IPAddress": "172.17.0.2",
"IPPrefixLen": 16,
"IPv6Gateway": "",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"MacAddress": "02:42:ac:11:00:02",
"DriverOpts": null
}
}
}
}
So in-short you need to know ip for your machine and the port on which docker daemon is listening to retrieve any sort of information from within the container.
Hope this helps, let me know.

Answer 2

Mount the docker socket to your container:
myservice:
volumes:
- /var/run/docker.sock:/var/run/docker.sock:ro
Then use a lib or directly query the docker api:
curl --unix-socket /var/run/docker.sock http://localhost/containers/json
This will return an array of all the running containers which includes the field:
{ Names: ['/proj_myservice_1', '/proj_myservice_2'] }
If you've scaled your containers up and are looking to communicate with the sibling containers inside a container, docker automatically detects this if you make requests to: http://myservice{:port} from inside your container. Docker will auto-discover the container and route you to a random container.