Docker commands you should know
Automatically start containers - restart policies
Restart policies to control whether your containers start automatically when they exit, or when Docker restart
Restart policies ensure that linked containers are started in the correct order.
Docker recommends that you use restart policies, and avoid using process managers to start containers.
To configure the restart policy for a container, use the –restart flag when using the docker run command. The value of the
flag can be:
--restart no: (default) Do not automatically restart the container.
--restart on-failure: Restart the container if it exits due to an error, which manifests as a non-zero exit code.
--restart always: Always restart the container if it stops. If it is manually stopped, it is restarted only when Docker daemon restarts or the container itself is manually restarted.
--restart unless-stopped: Similar to
always, except that when the container is stopped (manually or otherwise), it is not restarted even after Docker daemon restarts.
CMD directive ( Dockerfile)
It sets the default command for the image that runs if no other command is specified.
EXPOSE directive documents the ports that should be published when running a container from the image.
It sets environment variables that are made available in subsequent build steps and to containers at the runtime.
- The ADD directive can pull a file from an external URL.
- The ADD directive can extract an archive into the image.
Flattening an existing multi-layered image into a single layer
We can run a container from the image, export it, and then import it as a new image.
docker service ps nginxlist all of the replicas that are part of a service
view detailed metadata about a container
docker container inspect
find metadata about any container.
query metadata about any Docker object.
Command to view logs for all of the tasks in a service called
docker service logs my-service
This command will retrieve logs for all of the tasks in the service.
This command will evenly spread out tasks based upon the values of the availability_zone label.
docker service create --placement-pref spread=node.labels.availability_zone nginx
What flag should we use to specify a custom volume driver when creating a volume alongside a service that has
docker service create ?
Which storage driver is the default for current versions of CentOS/RHEL and Ubuntu?
Which of the following commands may result in the creation of a new named volume?
docker run -v my-vol:/tmp nginx
This command will create a new volume called
my-vol if one does not already exist under that name.
Which of the following commands will allow us to mount the
/my/path directory on the host to a container?
docker run -v /my/path:/tmp nginx
docker run --mount source=/my/path,destination=/tmp nginx
Which of the following statements about the
overlay network driver is accurate?
overlaynetwork driver dynamically creates networking components on the node when a relevant task gets scheduled on that node.
Which of the following tasks can we perform to set a custom DNS server for a container?
We can use the
Which of the following commands will create a new bridge network?
docker network create my-networkSince the bridge is the default, a new bridge network will generate even when
--driveris not specified.
Which of the following statements about Docker Content Trust (DCT) is accurate?
When Docker Content Trust is enabled, unsigned images will not be allowed to run on the system.
Which command allows us to create an encrypted overlay network?
docker network create --opt encrypted --driver overlay my-net
Which of the following is a secure method for allowing a Docker client to authenticate with a registry that uses a self-signed certificate?
We add the self-signed certificate as a trusted registry certificate under
The Docker daemon must run as root, so it is essential to ensure that it’s being protected and has limited access to it.
We can set
/etc/docker/daemon.json ; valid method that we can use for setting the default DNS server for all containers on a host
When creating a container, how would we specify that the container should be attached to an existing network called
We can use
docker run --network my-network nginx
When creating an
overlay network, what flag can we use to allow containers to attach to the network after it is created?
View container logs
Which component of the Docker Container Networking Model (CNM) is responsible for allocating IP addresses within Docker networks?
The IP Address Management (IPAM) Driver is responsible
The none driver implements sandboxes.
Which of the following commands will publish a service’s port, but only on nodes that are running a task for that service?
docker service create -p mode=host,published=8082,target=80 nginx
How would we create a volume called
new-volume without running a container?
We would run
docker volume create new-volume
Which of the following commands would we use to locate the data for a volume on the host?
docker volume inspect
Which storage driver is the default for CentOS 7 and earlier?
This command will return the container metadata, including the location of its data on the host.
docker container inspect <container>
What volume driver allows you to create and access external storage that can be shared across a Docker Swarm cluster using SSH?
vieux/sshfsThis is a custom driver that uses SSH to access remote storage from any node in the cluster.
What command would we use to list the services that are part of a stack called
docker stack services web-store
Which of the following commands will allow us to add a label to a Docker Swarm node?
docker node update --label-add <label> <node name>
Which of the following commands would successfully change the number of replicas to 5 in a service called my-service?
docker service update --replicas 5 my-service
docker service scale my-service=5
Daniel has some nodes with labels that specify the availability zone of each node. He wants to run a service that can run tasks on any node and that do not have the label availability_zone=east. Which command should he use?
docker service create --constraint node.labels.availability_zone!=east nginx
docker swarm unlock-keycommand
Which of the following best describes the procedure for backing up the Universal Control Plane (UCP) metadata?
Run a container from the
ucpimage with the
What Linux feature does Docker use in order to limit memory usage for containers?
Control groups (
How would we back up Docker Swarm?
Back up the contents of
/var/lib/docker/swarmon a Swarm manager.
How would we create a new swarm cluster?
docker swarm init
What does the HEALTHCHECK directive do?
It sets a command that will be used by the Docker daemon to determine whether the container is healthy.