Docker, how to get container information from a container?

Question

I would like to tell my docker containers about my configuration in the same way that you can get information about EC2 instances through metadata.

I can use (assuming docker listening on port 4243 )

 curl http://172.17.42.1:4243/containers/$HOSTNAME/json 

to get some of its data, but would like to know if there is a better way to at least get the full container identifier, because HOSTNAME is actually shortened to 12 characters, and the docker seems to be performing the “best match” on it.

Also, how can I get the external IP address of the docker host (except for access to EC2 metadata, which is related to AWS)

Answer 1

I found that the container identifier can be found in / proc / self / cgroup

So you can get the id with:

 cat /proc/self/cgroup | grep -o -e "docker-.*.scope" | head -n 1 | sed "s/docker-\(.*\).scope/\\1/" 

Answer 2

If not overridden, the hostname seems to be a short container identifier in Docker 1.12

 root@d2258e6dec11:/project# cat /etc/hostname d2258e6dec11 

Externally

 $ docker ps -a CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES d2258e6dec11 300518d26271 "bash" 5 minutes ago $ docker -v Docker version 1.12.0, build 8eab29e, experimental 

Answer 3

You can communicate with docker from inside the container using a unix socket via the Docker Remote API:

https://docs.docker.com/engine/reference/api/docker_remote_api/

In the container, you can find out the shortedned docker code by looking at $HOSTNAME env var. According to the document, there is a small chance of a collision, I think that for a small number of containers you have nothing to worry about. I do not know how to get the full identifier directly.

You can check the container in the same way as stated in banyan's answer:

 GET /containers/4abbef615af7/json HTTP/1.1 

Answer:

 HTTP/1.1 200 OK Content-Type: application/json { "Id": "4abbef615af7...... ", "Created": "2013.....", ... } 

Alternatively, you can pass the docker id to a container in the file. The file is on the "mounted volume", so it is transferred to the container:

 docker run -t -i -cidfile /mydir/host1.txt -v /mydir:/mydir ubuntu /bin/bash 

The docker identifier (abbreviated) will be in the file / mydir / host 1.txt in the container.

Answer 4

This will result in the full identifier of the container from the container:

 cat /proc/self/cgroup | grep "cpu:/" | sed 's/\([0-9]\):cpu:\/docker\///g' 

Answer 5

WARNING: You must understand the security risks of this method before considering it. John Risk Summary:

By giving the container access to /var/run/docker.sock , it is [trivially easy] to break out of /var/run/docker.sock provided by /var/run/docker.sock and gain access to the host machine. Obviously, this is potentially dangerous.

---

Inside the container, dockerId is your hostname. So you could:

• install docker-io package in your container with the same version as the host
• run it with --volume/var/run/docker.sock: /var/run/docker.sock --privileged
• finally run: docker inspect $(hostname) inside the container

Avoid this. Do this only if you understand the risks and have a clear risk reduction.

Answer 6

To make it simple,

• Container ID is the name of your host inside docker
• Container information is available inside / proc / self / cgroup

To get the host name,

 hostname 

or

 uname -n 

or

 cat /etc/host 

The output can be redirected to any file and read from the application. For example: # hostname > /usr/src//hostname.txt

Answer 7

Madaddy 's comment looks most elegant to me:

 CID=$(basename $(cat /proc/1/cpuset)) 

Answer 8

I found that in 17.09 there is the easiest way to do this in the docker container:

 $ cat /proc/self/cgroup | head -n 1 | cut -d '/' -f3 4de1c09d3f1979147cd5672571b69abec03d606afcc7bdc54ddb2b69dec3861c 

Or, as already mentioned, a shorter version with

 $ cat /etc/hostname 4de1c09d3f19 

Or simply:

 $ hostname 4de1c09d3f19 

Answer 9

Docker sets the default hostname of the container ID, but users can override this with --hostname . Check /proc instead:

 $ more /proc/self/cgroup 14:name=systemd:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 13:pids:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 12:hugetlb:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 11:net_prio:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 10:perf_event:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 9:net_cls:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 8:freezer:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 7:devices:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 6:memory:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 5:blkio:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 4:cpuacct:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 3:cpu:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 2:cpuset:/docker/7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 1:name=openrc:/docker 

Here is a handy single line file for retrieving the container ID:

 $ grep "memory:/" < /proc/self/cgroup | sed 's|.*/||' 7be92808767a667f35c8505cbf40d14e931ef6db5b0210329cf193b15ba9d605 

Answer 10

You can use this command line to identify the current container identifier (verified using docker 1.9).

 awk -F"-|/." '/1:/ {print $3}' /proc/self/cgroup 

Then, a small request to the Docker API (you can share /var/run/docker.sock) to get all the information.

Answer 11

 awk -F'[:/]' '(($4 == "docker") && (lastId != $NF)) { lastId = $NF; print $NF; }' /proc/self/cgroup 

Answer 12

Some published solutions have stopped working due to changes in the /proc/self/cgroup . Here is one GNU grep command that should be slightly more resilient to format changes:

 grep -o -P -m1 'docker.*\K[0-9a-f]{64,}' /proc/self/cgroup 

For reference, here are snippets of / proc / self / cgroup from docker containers that have been tested with this command:

Linux 4.4:

 11:pids:/system.slice/docker-cde7c2bab394630a42d73dc610b9c57415dced996106665d427f6d0566594411.scope ... 1:name=systemd:/system.slice/docker-cde7c2bab394630a42d73dc610b9c57415dced996106665d427f6d0566594411.scope 

Linux 4.8 - 4.13:

 11:hugetlb:/docker/afe96d48db6d2c19585572f986fc310c92421a3dac28310e847566fb82166013 ... 1:name=systemd:/docker/afe96d48db6d2c19585572f986fc310c92421a3dac28310e847566fb82166013 

Answer 13

Aside, if you have a container pid and want to get the docker ID of that container, a good way is to use nsenter in conjunction with the sed magic above:

nsenter -n -m -t pid -- cat /proc/1/cgroup | grep -o -e "docker-.*.scope" | head -n 1 | sed "s/docker-\(.*\).scope/\\1/"

Answer 14

The easiest way I've found is: docker inspect --format = "{{. Id}}"

Answer 15

Use docker inspect .

 $ docker ps # get conteiner id $ docker inspect 4abbef615af7 [{ "ID": "4abbef615af780f24991ccdca946cd50d2422e75f53fb15f578e14167c365989", "Created": "2014-01-08T07:13:32.765612597Z", "Path": "/bin/bash", "Args": [ "-c", "/start web" ], "Config": { "Hostname": "4abbef615af7", ... 

You can get ip as follows.

 $ docker inspect -format="{{ .NetworkSettings.IPAddress }}" 2a5624c52119 172.17.0.24