I want to generate/get a Dockerfile for an image that is pushed to registry, one that I don't have locally, without docker pull that image. I know it's possible to do this with docker CLI if the image already exists locally.
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As of now, I am learning Docker. This reference has mentioned two ways of pulling an image from the Docker registry. Can anyone explain this in simple terms?
Does this mean that we cannot get updates on a pulled image if we use docker image pull command?
They are the same command. From the documentation you linked:
To download a particular image, or set of images (i.e., a repository), use docker image pull (or the docker pull shorthand).
There are many "shortand commands" like:
docker push for docker image push
docker run for docker container run
...
What is the difference between docker pull and docker image pull commands?
None.
Can anyone explain this in simple terms?
They are the same.
Does this mean that we cannot get updates on a pulled image if we use docker image pull command?
No.
Also https://forums.docker.com/t/docker-pull-imagename-vs-docker-image-pull-imagename/59283
I have a docker image. I want to analyze the docker image history, for this I can use docker image history command in the docker installed environment.
But when am working in a Openshift cluster, I may not have the access to the docker command here. So here I want get the docker history command result for the given image.
So basically I have a docker image and I don't have docker installed there. In this case how can we get the history of that docker image?
Can anyone please help me on this?
You can get the registry info either via curl or skopeo inspect. But the rest of the metadata is stored inside the image itself so you do have to download at least the final layer.
Usually according to docs In order to build a docker Image I need to follow these steps:
Create a Dockerfile for my application.
Run docker build . Dockerfile where the . is the context of my application
The using docker run run my image into a container.
Commit my image into a container
Then using docker push push the image into a container.
Though sometimes just launching the image into a container seems like a waste of time because I can tag my images using the parameter -t into the docker build command. So there's no need to commit a container as an image.
So is neseserily to commit a running container as an image?
You don't need to run and commit. docker commit allows you to create a new image from changes made on existing container.
You do need to build and tag your image in a way that will enable you to push it.
docker build -t [registry (defaults to docker hub)]/[your repository]:[image tag] [docker file context folder]
for example:
docker build -t my-repository/some-image:image-tag .
And then:
docker push my-repository/some-image:image-tag
This will build an image from a docker file found in the current folder (where you run the docker build command). The repository in this case is my-repository, the image name is some-image and it's tag is image-tag.
Also please note that you'll have to perform docker login with your credentials to docker hub before you are able to actually push the image.
You can also tag an existing image without rebuilding it. This is useful if you want to push an existing image to a different registry or if you want to create a different image tag. for example:
docker tag my-repository/some-image:image-tag localhost:5000/my-repository/some-image:image-tag
This will add a new tag to the image from the previous example. Note the registry part added (localhost:5000). If you call docker push on that tag (docker push localhost:5000/my-repository/some-image:image-tag) the image will be pushed to a registry found on localhost:5000 (of course you need the registry up and running before trying to push).
There's no need to do so. In order to prove that you can just tag the image and push it into the registry here's an example:
I made the following Dockerfile:
FROM alpine
RUN echo "Hello" > /usr/share/hello.txt
ENTRYPOINT cat /usr/share/hello.txt
Nothing special just generates a txt file and shows its content.
Then I can build my image using tags:
docker build . -t ddesyllas/dummy:201201241200 -t ddesyllas/dummy:201201241200
And then just push them to the registry:
$ docker push ddesyllas/dummy
The push refers to repository [docker.io/ddesyllas/dummy]
1aa99de3dbec: Pushed
6bc83681f1ba: Mounted from library/alpine
201908241504: digest: sha256:93e8407b1d52620aeadd769486ef1402b9e310018cae0972760f8c1a03377c94 size: 735
1aa99de3dbec: Layer already exists
6bc83681f1ba: Layer already exists
latest: digest: sha256:93e8407b1d52620aeadd769486ef1402b9e310018cae0972760f8c1a03377c94 size: 735
And as you can see from the output you can just build the tags and push it directly, good for your ci/cd pipeline. Though, generally speaking, you may need to launch the application into a container in order to do acceptance and other type of tests (eg. end-to-end tests).
I have 2 hosts running the same docker customized image. I have modified the image on host 1 and saved the image to a custom.tar. If I take that image and load it onto host 2 will it just update or should I remove the old docker image first?
There are 2 ways to do that with repository and without repository using load and save.
With repository below are the steps.
Log in on Docker Hub
Click on Create Repository.
Choose a name and a description for your repository and click
Create.
Log into the Docker Hub from the command line
docker login --username=yourhubusername --email=youremail#company.com
tag your image
docker tag <existing-image> <hub-user>/<repo-name>[:<tag>]
Push your image to the repository you created
docker push <hub-user>/<repo-name>:<tag>
Pull the image to host 2
docker pull <hub-user>/<repo-name>:<tag>
This will add the image to docker hub and available on internet and now you can pull this image to any system.
With this approach you can keep the same images with different tags on system. But if you don't need old images better to delete that to avoid junk.
Without docker hub.
This command will create tar bundle.
docker save [OPTIONS] IMAGE [IMAGE...]
example: docker save busybox > busybox.tar
Load an image from a tar archive or STDIN
docker load [OPTIONS]
example:docker load < busybox.tar.gz
Recommended: Docker hub or DTR approach easy to manage unless you have bandwidth issue in case your file is large.
Refer:
Docker Hub Repositories
I would like to be able to pull a docker image from dockerhub and edit the dockerfile.. I am wondering if dockerhub actually downloads the dockerfile to the localhost and to where it is stored (I am running it from a MAC).
You dont download the docker image and edit their Dockerfile. The Dockerfile is an instruction set on how to build an image. Once the image is made, theres no going backwards. However if its on Dockerhub there should be a link to the Dockerfile. Look around at the page for links to the Dockerfile. Probably just a link to Github.
Once you have the dockerfile you then build it. For instance if you have a terminal open in the same folder as a Dockerimage file you could run
docker build -t myimage .
where myimage is the tag of your image. You will then have an instance of myimage on your local machine.
Also you can make a docker file that extends theres using FROM. For instance your docker file might start with
FROM java:6b38-jdk
# append to their image.
An image does not include a complete Dockerfile. When pulling an image you get an image manifest along with the required file system layers.
You can see some of the build steps with docker history --no-trunc IMAGE but it's not the complete Dockerfile.
There are utilities that try and generate a Dockerfile from the image history