Docker Tipps

Container lifecycle

Normally if you run a container without options it will start and stop immediately, if you want keep it running you can use the command, docker run -td container_id this will use the option -t that will allocate a pseudo-TTY session and -d that will detach automatically the container (run container in background and print container ID).

If you want a transient container, docker run --rm will remove the container after it stops.

If you want to map a directory on the host to a docker container, docker run -v $HOSTDIR:$DOCKERDIR. Also see Volumes.

If you want to remove also the volumes associated with the container, the deletion of the container must include the -v switch like in docker rm -v.

There's also a logging driver available for individual containers in docker 1.10. To run docker with a custom log driver (i.e., to syslog), use docker run --log-driver=syslog.

Another useful option is docker run --name yourname docker_image because when you specify the --name inside the run command, this will allow you to start and stop a container by calling it with the name you specified when you created it.

Starting and Stopping

If you want to detach from a running container, use Ctrl + p, Ctrl + q.

Capabilities

Linux capabilities can be set by using cap-add and cap-drop. See https://docs.docker.com/engine/reference/run/#/runtime-privilege-and-linux-capabilities for details. This should be used for greater security.

To mount a FUSE based filesystem, you need to combine both --cap-add and --device:

docker run --rm -it --cap-add SYS_ADMIN --device /dev/fuse sshfs

Give access to a single device:

docker run -it --device=/dev/ttyUSB0 debian bash

Give access to all devices:

docker run -it --privileged -v /dev/bus/usb:/dev/bus/usb debian bash

Info

docker ps -a shows running and stopped containers.

docker stats --all shows a list of all containers, default shows just running.

Images

Lifecycle

Info

Cleaning up

While you can use the docker rmi command to remove specific images,  docker image prune is available for removing unused images. See Prune.

Load/Save image

Load an image from file:

docker load < my_image.tar.gz

Save an existing image:

docker save my_image:my_tag | gzip > my_image.tar.gz

Import/Export container

Import a container as an image from file:

cat my_container.tar.gz | docker import - my_image:my_tag

Export an existing container:

docker export my_container | gzip > my_container.tar.gz

Difference between loading a saved image and importing an exported container as an image

Loading an image using the load command creates a new image including its history.

Importing a container as an image using the import command creates a new image excluding the history which results in a smaller image size compared to loading an image.

Volumes

Docker volumes are free-floating filesystems. They don't have to be connected to a particular container.

Lifecycle

Info

Volumes are useful in situations where you can't use links (which are TCP/IP only). For instance, if you need to have two docker instances communicate by leaving stuff on the filesystem.

You can mount them in several docker containers at once, using docker run --volumes-from.

Because volumes are isolated filesystems, they are often used to store state from computations between transient containers. That is, you can have a stateless and transient container run from a recipe, blow it away, and then have a second instance of the transient container pick up from where the last one left off.

You can use remote NFS volumes if you're feeling brave.

Exposing ports

Exposing incoming ports through the host container is fiddly but doable.

This is done by mapping the container port to the host port (only using localhost interface) using -p:

docker run -p 127.0.0.1:$HOSTPORT:$CONTAINERPORT \
  --name CONTAINER \
  -t someimage

You can tell Docker that the container listens on the specified network ports at runtime by using EXPOSE:

EXPOSE <CONTAINERPORT>

Note that EXPOSE does not expose the port itself - only -p will do that.

If you forget what you mapped the port to on the host container, use docker port to show it:

docker port CONTAINER $CONTAINERPORT

Sources

Tipps

Prune

The new Data Management Commands have landed as of Docker 1.13:

df

docker system df presents a summary of the space currently used by different docker objects.

Last IDs

alias dl='docker ps -l -q'
docker run ubuntu echo hello world
docker commit $(dl) helloworld

Commit with command (needs Dockerfile)

docker commit -run='{"Cmd":["postgres", "-too -many -opts"]}' $(dl) postgres

Get IP address

docker inspect $(dl) | grep -wm1 IPAddress | cut -d '"' -f 4

Or with jq installed:

docker inspect $(dl) | jq -r '.[0].NetworkSettings.IPAddress'

Or using a go template:

docker inspect -f '{{ .NetworkSettings.IPAddress }}' <container_name>

Or when building an image from Dockerfile, when you want to pass in a build argument:

DOCKER_HOST_IP=`ifconfig | grep -E "([0-9]{1,3}\.){3}[0-9]{1,3}" | grep -v 127.0.0.1 | awk '{ print $2 }' | cut -f2 -d: | head -n1`
echo DOCKER_HOST_IP = $DOCKER_HOST_IP
docker build \
  --build-arg ARTIFACTORY_ADDRESS=$DOCKER_HOST_IP 
  -t sometag \
  some-directory/

Get port mapping

docker inspect -f '{{range $p, $conf := .NetworkSettings.Ports}} {{$p}} -> {{(index $conf 0).HostPort}} {{end}}' <containername>

Find containers by regular expression

for i in $(docker ps -a | grep "REGEXP_PATTERN" | cut -f1 -d" "); do echo $i; done

Get Environment Settings

docker run --rm ubuntu env

Kill running containers

docker kill $(docker ps -q)

Delete all containers (force!! running or stopped containers)

docker rm -f $(docker ps -qa)

Delete old containers

docker ps -a | grep 'weeks ago' | awk '{print $1}' | xargs docker rm

Delete stopped containers

docker rm -v $(docker ps -a -q -f status=exited)

Delete containers after stopping

docker stop $(docker ps -aq) && docker rm -v $(docker ps -aq)

Delete dangling images

docker rmi $(docker images -q -f dangling=true)

Delete all images

docker rmi $(docker images -q)

Show image dependencies

docker images -viz | dot -Tpng -o docker.png

Monitor system resource utilization for running containers

To check the CPU, memory, and network I/O usage of a single container, you can use:

docker stats <container>

For all containers listed by ID:

docker stats $(docker ps -q)

For all containers listed by name:

docker stats $(docker ps --format '{{.Names}}')

For all containers listed by image:

docker ps -a -f ancestor=ubuntu

Remove all untagged images:

docker rmi $(docker images | grep “^” | awk '{split($0,a," "); print a[3]}')

Remove container by a regular expression:

docker ps -a | grep wildfly | awk '{print $1}' | xargs docker rm -f

Remove all exited containers:

docker rm -f $(docker ps -a | grep Exit | awk '{ print $1 }')

Volumes can be files

Be aware that you can mount files as volumes. For example you can inject a configuration file like this:

# copy file from container
docker run --rm httpd cat /usr/local/apache2/conf/httpd.conf > httpd.conf

# edit file
vim httpd.conf

# start container with modified configuration
docker run --rm -it -v "$PWD/httpd.conf:/usr/local/apache2/conf/httpd.conf:ro" -p "80:80" httpd

Auto restart container

The second container will restart the first container which is mentioned in the restart command.

services:
  app:
    image: nginx:alpine
    ports: ["80:80"]
    restart: unless-stopped

  restarter:
    image: docker:cli
    volumes: ["/var/run/docker.sock:/var/run/docker.sock"]
    command: ["/bin/sh", "-c", "while true; do sleep 86400; docker restart app_app_1; done"]
    restart: unless-stopped