Docker provides a way to run the container using docker run
Or just pull the container image using docker pull
Found a doc showing mapping between docker commands and kubectl.
Can't find docker pull equivalent in this doc.
If there is no any such equivalent to docker pull, then is there any way to just pull an image using kubectl cli.
In short - no, there is not.
And why would there be? Kubernetes is an orchestration tool for Docker, it will automatically pull pods for you if it needs them, so there's really no need to have a command to pull containers manually.
I think there isn't a kubectl ... equivalent and some of the reasons might be:
they are not equivalent 🙂. When you docker pull an image, you are planning to use it afterwards on your docker host. When you kubectl ... a deployment, you want the platform to schedule everything. For example if you have many worker nodes and the replicas are going to be scheduled to only two of them, then the other nodes don't have to pull the image.
kubectl is a tool that talks to the API server to control the cluster. It would be wrong to make it also responsible for container images (see, Leaky Abstractions) since you have available a lower level tool that talks to the Container Runtime Interface for that: crictl.
k8s-master:~$ crictl --help
NAME:
crictl - client for CRI
USAGE:
crictl [global options] command [command options] [arguments...]
VERSION:
v1.12.0
COMMANDS:
attach Attach to a running container
create Create a new container
exec Run a command in a running container
version Display runtime version information
images List images
inspect Display the status of one or more containers
inspecti Return the status of one or more images
inspectp Display the status of one or more pods
logs Fetch the logs of a container
port-forward Forward local port to a pod
ps List containers
pull Pull an image from a registry
...
pic from: www.aquasec.com/wiki/display/containers/Kubernetes+Architecture+101
what takes place with container run-times under the hood is complicated and keeps evolving. Think about this, people started creating Kubernetes clusters and the container engine used was Docker. Then Docker adopted containerd so we had Kubernetes on top of Docker on top of containerd, which caused problems like this:
Users won't see Kubernetes pulled images with the docker images command... And vice versa, Kubernetes won't see images created by docker pull, docker load or docker build commands...
source / more details: Kubernetes Containerd Integration Goes GA
crictl pull <image name>
There is no need to pull by kubernetes in cli.
Why?
Becuase when you run kubectl create -f template.yml it containe an image and it cjecked that the image is exist or not. If it does not exist it pull image automatically.
You will not find equivalent of docker pull in Kubernetes because this command is related to images management. Explanation below.
One of Docker features is abbility to create Images. You can create your own image using Dockerfile (docker build .) or pull from Docker Hub which contains many pre-built images.
If you use pull command it will just download image, it will not deploy any container.
$ docker pull hello-world
Using default tag: latest
latest: Pulling from library/hello-world
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-world latest fce289e99eb9 5 months ago 1.84kB
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
As you see, $ docker pull will only display download image. As Docker is also responsible for image management you can pull or push images to repository (DockerHub).
To create container in Docker you have to use $ docker run. This command will automatically download image and run container.
$ docker run --name mynginx -p 80:80 -d nginx
Unable to find image 'nginx:latest' locally
latest: Pulling from library/nginx
...
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
4abf804611a8 nginx "nginx -g 'daemon of…" 4 minutes ago Up 4 minutes 0.0.0.0:80->80/tcp mynginx
In short:
Create adds a writeable container on top of your image and sets it up for running whatever command you specified in your CMD. The container ID is reported back but it’s not started.
Start will start any stopped containers. This includes freshly created containers.
Run is a combination of create and start. It creates the container and starts it.
Kubernetes is container-orchestration system so it is not responsible for creating or edit images. That is why you will not find equivalent of docker pull (download only image).
Commands like kubectl apply -f <deployment> with image inside YAML file or kubectl run nginx --image=nginx are based on images from DockerHub (more like docker create).
Hope it helped.
It could be a bit tricky, but it is possible to achieve similar to docker pull results using kubectl. You just need to know how to exit the containers with zero exit code.
The idea is to pull several images on all nodes in the Kubernetes cluster.
For doing this you could create a DaemonSet which will try to create Pods on every applicable node in the cluster. To pull several images at once, just add several initContainers to the DaemonSet template. ImagePullPolicy set to IfNotPresent, restartPolicy set to Never. Set command individually to each initContainer to make it exit successfully. You need something like sh -c "exit 0", just ensure that container has sh binary inside, or use another possible command that usually gives you zero exit code: <appname_binary> version or <appname_binary> --help.
After applying that DaemonSet to the cluster, Kubernetes creates Pods from DaemonSet templates on each node and runs each initContainer in the Pod in order of presence. Before starting each container kubelet pulls the image required to run that container.
When you see that all DaemonSet Pods completed successfuly - you can be sure that on every node you have all images, required for running those containers.
You can play with nodeAffinity or taints/tolerations if you want to run the DaemonSet only on specific nodes.
I'm new to docker.Most of the tutorials on docker cover the same thing.I'm afraid I'm just ending up with piles of questions,and no answers really. I've come here after my fair share of Googling, kindly help me out with these basic questions.
When we install a docker,where it gets installed? Is it in our computer in local or does it happen in cloud?
Where does containers get pulled into?I there a way I can see what is inside the container?(I'm using Ubuntu 18.04)
When we pull an image.Docker image or clone a repository from
Git.where does this data get is stored?
Looks like you are confused after reading to many documents. Let me try to put this in simple words. Hope this will help.
When we install a docker,where it gets installed? Is it in our
computer in local or does it happen in cloud?
We install the docker on VM be it you on-prem VM or cloud. You can install the docker on your laptop as well.
Where does containers get pulled into?I there a way I can see what is
inside the container?(I'm using Ubuntu 18.04)
This question can be treated as lack of terminology awareness. We don't pull the container. We pull the image and run the container using that.
Quick terminology summary
Container-> Containers allow you to easily package an application's code, configurations, and dependencies into a template called an image.
Dockerfile-> Here you mention your commands or infrastructure blueprint.
Image -> Image gets derived from Dockerfile. You use image to create and run the container.
Yes, you can log inside the container. Use below command
docker exec -it <container-id> /bin/bash
When we pull an image.Docker image or clone a repository from
Git.where does this data get is stored?
You can pull the opensource image from Docker-hub
When you clone the git project which is docerized, you can look for Dockerfile in that project and create the your own image by build it.
docker build -t <youimagenae:tag> .
When you build or pull the image it get store in to your local.
user docker images command
Refer the below cheat-sheet for more commands to play with docker.
The docker daemon gets installed on your local machine and everything you do with the docker cli gets executed on your local machine and containers.
(not sure about the 1st part of your question). You can easily access your docker containers by docker exec -it <container name> /bin/bash for that you will need to have the container running. Check running containers with docker ps
(again I do not entirely understand your question) The images that you pull get stored on your local machine as well. You can see all the images present on your machine with docker images
Let me know if it was helpful and if you need any futher information.
I have followed this guide from Google documentation in order to be able to push a custom Docker image to Google Container Registry and then be able to start a new GCE instance with this image. At first I wanted to try using an anaconda3 public image from docker hub without any modification (in order to test).
So here is the steps I have done so far after installing gcloud and docker:
gcloud auth configure-docker -> configured docker with my gcloud crendentials
docker pull continuumio/anaconda3 -> pulled the public image
docker tag continuumio/anaconda3 eu.gcr.io/my-project-id/anaconda3 -> tagged the local image with the registry name as specified in the doc
docker push eu.gcr.io/my-project-id/anaconda3 -> pushed the image to GCR
Good ! I am now able to see my image trough GCR interface, and also able to deploy it with GCE. I choose to deploy it with a f1-micro instance, Container-Optimized OS 67-10575.62.0 stable, 10 Go boot disk, Allow HTTP traffic, etc.
But when I connect with ssh to the freshly new created VM instance, I can't find anaconda3 librairies (which are supposed to be created in /opt/conda). Instead, I can see a /opt/google directory which makes me think that the image has not been deployed correctly and GCE is using a default image...
So I tried to check if the image was pushed correctly in GCR, so I decided to delete my local image and pull it once again from GCR:
docker rmi -f eu.gcr.io/my-project-id/anaconda3
docker pull eu.gcr.io/my-project-id/anaconda3:latest
I run the image
docker run -t -i eu.gcr.io/my-project-id/anaconda3
and I can see that everything is fine, I have anaconda3 installed correctly inside /opt/conda with all the toolts needed (Pandas, Numpy, Jupyter notebook, etc.)
I tried to find people with the same problem as me without any success... maybe I have done something wrong in my proccess ?
Thanks !
TL;DR My problem is that I have pushed an anaconda3 image on Google GCR, but when I launch a virtual instance with this image, I do not have anaconda on it
It's normal that you can't find anaconda libraries installed directly on the GCE instance.
Actually, when you choose to deploy a container image on a GCE VM instance, a Docker container is started from the image you provide (in your example, eu.gcr.io/my-project-id/anaconda3). The libraries are not installed on the host, but rather inside that container (run docker ps to see it, but normally it has the same name as your VM instance). If you run something like :
docker exec -it <docker_container_name> ls /opt/conda
Then you should see the anaconda libraries, only existing inside the container.
When you run docker run -t -i eu.gcr.io/my-project-id/anaconda3, you're actually starting the container and running an interactive bash session inside that container (see the CMD here). That's why you can find anaconda libraries : you are inside the container!
Containerization software (docker here) provides isolation between your host and your containers. I'll suggest you to read documentation about containerization, Docker and how to run containers on Container-Optimized OS.
Is it possible to pull an image from another docker machine without having to install the docker repository?
I got 2 docker machines for development and i would like to deploy an image on the second docker machine that i have build with the first one.
Is this possible?
If you have created your docker servers using docker-machine then you could do an export/import using remote access to the docker agents on each server.
docker $(docker-machine config server1) export exampleimage:1.0 | docker $(docker-machine config server2) import - exampleimage:1.0
But....it would be a lot simpler to just rebuild the image on the second server, using the same Dockerfile.
This question already has answers here:
What is the difference between a Docker image and a container?
(31 answers)
Closed 3 years ago.
What's the difference between a container and an image in Docker? In the Get started with Docker tutorial these terms are both used, but I do not understand the difference.
Can anybody please shed some light?
Images are frozen immutable snapshots of live containers. Containers are running (or stopped) instances of some image.
Start with the base image called 'ubuntu'. Let's run bash interactively within the ubuntu image and create a file. We'll use the -i and -t flags to give us an interactive bash shell.
$ docker run -i -t ubuntu /bin/bash
root#48cff2e9be75:/# ls
bin boot dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var
root#48cff2e9be75:/# cat > foo
This is a really important file!!!!
root#48cff2e9be75:/# exit
Don't expect that file to stick around when you exit and restart the image. You're restarting from exactly the same defined state as you started in before, not where you left off.
$ docker run -i -t ubuntu /bin/bash
root#abf181be4379:/# ls
bin boot dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var
root#abf181be4379:/# exit
But, the container, now no longer running, has state and can be saved (committed) to an image.
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
abf181be4379 ubuntu:14.04 /bin/bash 17 seconds ago Exited (0) 12 seconds ago elegant_ardinghelli
48cff2e9be75 ubuntu:14.04 /bin/bash About a minute ago Exited (0) 50 seconds ago determined_pare
...
Let's create an image from container ID 48cff2e9be75 where we created our file:
$ docker commit 48cff2e9be75 ubuntu-foo
d0e4ae9a911d0243e95556e229c8e0873b623eeed4c7816268db090dfdd149c2
Now, we have a new image with our really important file:
$ docker run ubuntu-foo /bin/cat foo
This is a really important file!!!!
Try the command docker images. You should see your new image ubuntu-foo listed along with the ubuntu standard image we started with.
An image is an ordered collection of root filesystem changes and the corresponding execution parameters for use within a container runtime. Images are read-only.
https://docs.docker.com/glossary/?term=image
A container is an active (or inactive if exited) stateful instantiation of an image.
https://docs.docker.com/glossary/?term=container
Using an object-oriented programming analogy, the difference between a Docker image and a Docker container is the same as that of the difference between a class and an object. An object is the runtime instance of a class. Similarly, a container is the runtime instance of an image.
An object gets created only once when it is instantiated. Similarly, a container can be running or stopped. Containers are created out of an image, though this might not always be the case. The following example creates an Apache server image, runs the image, lists the images and then lists the containers:
Create a Dockerfile with the following contents:
FROM httpd:2.4
Install Apache server
sudo docker build -t my-apache2 .
Run the image
sudo docker run -it --rm --name my-running-app my-apache2
List Docker images
sudo docker images
List the running Docker containers
docker ps
List all containers
docker ps -a
List latest created containers
docker ps -l
An image is basically an immutable template for creating a container. It's easier to understand the difference between an image and container by considering what happens to an image to turn it into a container.
The Docker engine takes the image and adds a read-write filesystem on top, then initialises various settings. These settings include network options (IP, port, etc.), name, ID, and any resource limits (CPU, memory). If the Docker engine has been asked to run the container it will also initialise a process inside it. A container can be stopped and restarted, in which case it will retain all settings and filesystem changes (but will lose anything in memory and all processes will be restarted). For this reason a stopped or exited container is not the same as an image.
DockerFile --(Build)--> DockerImage --(run)--> DockerContainer
DockerFile is what you or developer write code to do something (ex- Install)
Docker Image is you get when you build docker file .
Docker Container is you get when you run your Docker image
We can get Docker Image from docker hub by pulling and then run it to get container .
Images [like vm]
Read only template used to create containers
Buuilt by you or other Docker users
Stored in the Docker Hub or your local Registry
Containers [like a runing machine]
Isolated application platform
Contains everything needed to run your application
Based on images
In Docker, it all begins with an image. An image is every file that makes up just enough of the operating system to do what you need to do. Traditionally you'd install a whole operating system with everything for each application you do. With Docker you pair it way down so that you have a little container with just enough of the operating system to do what you need to do, and you can have lots and lots of these efficiently on a computer.
Use docker images to see the installed images and docker ps to see the running images.
When you type docker run it takes the image, and makes it a living container with a running process. I tend to use:
docker run -ti <image>:<tag> bash
Lastly, images have their own set of ids and containers have their own set of ids - they don't overlap.
Containers are based on images. An image needs to be passed to the Dockers run command.
Example:
BusyBox image
http://i.stack.imgur.com/eK9dC.png
Here we specify an image called busybox. Docker does not have this image locally and pulls it from a public registry.
A registry is a catalog of Docker images that the Docker client can communicate with and download image from. Once the image is pulled, Docker starts a container and execute the echo hello world command.
Images: The filesystem and metadata needed to run containers. They can be thought of as an application packaging format that includes all of the dependencies to run the application, and default settings to execute that application. The metadata includes defaults for the command to run, environment variables, labels, and healthcheck command.
Containers: An instance of an isolated application. A container needs the image to define its initial state and uses the read-only filesystem from the image along with a container specific read-write filesystem. A running container is a wrapper around a running process, giving that process namespaces for things like filesystem, network, and PIDs.
When you execute a docker run command, you provide an image on the command line, along with any configurations, and docker returns a container based off of that image definition and configurations you provided.
References: to the docker engine, an image is just an image id. This is a unique immutable hash. A change to an image results in creating a new image id. However, you can have one or more references pointing to an image id, not unlike symbolic links. And these references can be updated to point to new image id's. Note that when you create a container, docker will resolve that reference at the time of container creation, so you cannot update the image of a running container. Instead, you create a new image, and create a new container based on that new image.
Layers: Digging a bit deeper, you have filesystem layers. Docker assembles images with a layered filesystem. Each layer is a read-only set of changes to the filesystem, and that layer is represented by a unique hash. Using these read-only layers, multiple images may extend another, and only the differences between those images need to be stored or transmitted over the network. When a Docker container is run, it receives a container specific read-write filesystem layer unique to that container, and all of the image layers are assembled with that using a union filesystem. A read is processed through each layer until the file is found, a deletion is found, or the file is not found in the bottom layer. A write performs a copy-on-write from the image read-only layer to the container specific read-write layer. And a deletion is recorded as a change to the container specific read-write layer. A common step in building images is to run a command in a temporary container based off the previous image filesystem state and save the resulting container specific layer as a layer in the new image.
Docker Images:
It contains a list of commands and instruction on how to build and run a container. So basically Images contains all the data and metadata required to fire up a container(also called blueprint).We can't lunch a container without specifying Images.
$docker images centos
List all the available version of centos.
Docker Container:
Containers are lunch from Images so we can say container is the running instance of an Images.
Container is a runtime construct, unlike Images which is build time construct.
The official difference is that the container is the last layer which is writable whereas the layers below are only readable and they belong to your image. The intuitive difference is that the docker instance is the instance virtualized by your docker daemon and the running your image, it operates within an isolated section of your kernel (this process is hidden from you). The image however is static, it doesn't run, it is just a pile of layers (static files). If we would relate this paradigm to object-oriented programming, the image is your class definition, whereas your docker instance is your class spawned object that resides in memory.
I have written a tutorial to reinforce your docker knowledge intuition:
http://javagoogleappspot.blogspot.com/2018/07/docker-basics.html
Image is the photo made from your phone.
Container is the phone.