Is there a possibility to force pull of docker image?
I have redeployed docker image to another repository, but when I invoke
docker pull anotherrepo:port/my/image
nothing gets downloaded, instead I get info:
Digest: sha256:somehash
and that image is up to date.
docker rm/rmi doesn't work because the image is downloaded from originalrepo:port/my/image and I don't want to stop/delete it onyl for test purposes.
Is there possible to force pull to check if the image is correctly pushed?
The following should work. You add a temporary tag to avoid deletion of the image, delete the original tag and then pull:
docker tag "$originalTag" "tmpTag"
docker rmi "$originalTag"
docker pull "$originalTag"
docker rmi "tmpTag"
I think the answer lies in digests.
Images that use the v2 or later format have a content-addressable identifier called a digest. As long as the input used to generate the image is unchanged, the digest value is predictable.
Source: https://docs.docker.com/engine/reference/commandline/images/#list-the-full-length-image-ids
Maybe you don't need to verify if the push was successful, as Docker could be doing that automatically by using digests, but I'm not sure if this is indeed the case.
The only other way I can think of would be to pull from a different machine which has access to the new repository.
Related
I know Watchtower (https://github.com/v2tec/watchtower), but would like to understand if there is a way that I check for docker image updates without pull (downloading it)
I seems that if I ie. use docker pull pihole:latest it download the image, no matter if it the newest or already on my device.
I would like to get the digest or image id from the docker hub, so I can compare it with my local image id
How does docker handle digests?
I can see in plain text, when I run docker image --inspect, the digest of an image. And there's also the thing that local images don't have a digest until I push them to a registry (and AFAIK, if I push an image to various registries, it will have various digests, but never tried that).
I fear that docker might be actually using that info instead of calculating the hash every time that I use or pull an image.
Is there a way to actually tell docker: "Hey, I want you to recheck right now the hash of the image contents. Are they the exact same as when I first created the image? Or has someone manipulated it ever?"
And: does docker really calculate that hash every time an image is run (by digest), or at least every time an image is pulled (by digest)?
The digest is calculated on push and pull to a registry. It's a sha256 checksum of the image manifest, which is current versions of docker is independent of the registry (the older schema v1 syntax included the repository/tag in the manifest that resulted in the digest changing depending on the image name). The layer digests are included in that manifest, and those digests on the registry are compressed tar files. Once the files have been extracted on the local docker engine, they aren't reverified, and I'm not aware of a command yet that would verify the files under /var/lib/docker have not been changed since the image was pulled.
I'm using some docker images, which I have pulled from a registry:
docker pull registry.example.com/project/backend:latest
docker pull registry.example.com/project/frontend:latest
Now there is a new version on the server registry. If I do a new pull, I will overwrite the current images. But I need to keep the current working images in case I do get some problems with the newest latest images.
So, how do I create a kind of backup of my running backend:latest and frontend:latest? After that I can pull the latest latest image and in case I need to, I can use the old working images...
To keep the current image on your local environment you can use docker tag
docker tag SOURCE_IMAGE[:TAG] TARGET_IMAGE[:TAG]
For example:
docker tag registry.example.com/project/backend:latest registry.example.com/project/backend:backup
Then when you pull the latest, the registry.example.com/project/backend:backup still existing
Pulling an image never deletes an existing image. However, if you have an image with the same name, the old image will become unnamed, and you'll have to refer to it by its image ID.
You've now seen the downside to using :latest tags. This is why it is better to reference an image by a specific version tag that the maintainer won't re-push.
First, you shouldn't be using latest in production environments. Rather define a tag you confirmed working.
And instead of executing stuff in an image to set it up, you should write a Dockerfile and make the installation repeatable and create your local image. That's actually one of the main reasons why docker is used.
I'm trying to download a tagged docker image
docker pull clkao/postgres-plv8:10-2
and, in a compose file,
postgres:
image: clkao/postgres-plv8:10-2
But receive a manifest not found exception.
Unless I'm mistaken, that tag exists in Docker Hub, however I notice that it doesn't appear on the tags list.
Am I doing something wrong? Or is this perhaps an issue with Docker Hub or the way that repo has been set up?
If it isn't 'my fault', what's a recommendation to move forward? Create my own Dockerfile perhaps?
You might also try
docker pull -a <image>.
The -a will pull all versions of that image, which at least lets you know what is there.
(This is less useful if you really need a specific version, but helped me when I tried to pull an image that for some reason did not have a 'latest' tag.)
Edit: This is actually a really bad idea, since it will pull down the entire history, which for many repositories could be many GB. Better to go look at the repository site and see what tag you want. Note to self: don't post answers when you are tired. :-(
You get the error message because there exist no tag with "10-2".
You can try to figure out why and contact the repository owner or you can try to build your own one.
I just got over this "manifest for / not found: manifest unknown: The named manifest is not known to the registry."
Using
docker login <repo>
Check the docker's image also not only that the tag exists, I was trying to run Flyway version 5.0.1 for an image flyway/flyway which version did not exist, it existed only in version flyway/flyway:latest it seems, whereas 5.0.1 existed and I pulled it but in/from a different repository name, with repository name boxfuse/flyway.
for the error message 'docker manifest unknown'
When you use docker pull, without a tag, it will default to the tag :latest. Make sure that when we are building a image add tag latest or we can access the image by the tag name after image name with colon
I think you are trying to tag your image as v8.10.2. Make sure while tagging image locally you use same tag which you want to pull in future. So steps will be like below:
docker build -t clkao/postgres-pl:v8.10.2 .
docker push clkao/postgres-pl:v8.10.2
docker pull clkao/postgres-pl:v8.10.2
If this is from Git via docker.pkg.github.com then you need to switch to use ghcr.io. The former is deprecated and does not support the manifest endpoint so some docker clients, when they attempt to download various resources, fail with this error message. If you instead publish your image to ghcr (Github Container Repository), the docker image pulling process should complete successfully.
cd <dir with Dockerfile in it>
docker build -f Dockerfile -t ghcr.io/<org_id>/<project_id>:<version> .
docker push ghcr.io/<org_id>/<project_id>:<version>
More info here: https://docs.github.com/en/packages/working-with-a-github-packages-registry/migrating-to-the-container-registry-from-the-docker-registry
Note: The Container registry is currently in public beta and subject
to change. During the beta, storage and bandwidth are free. To use the
Container registry, you must enable the feature preview. For more
information, see "Introduction to GitHub Packages" and "Enabling
improved container support with the Container registry."
Is there any way to prevent images being uploaded to docker hub with the same tags as existing images? Our use case is as follows.
We deploy to production with a docker-compose file with the tags of images as version numbers. In order to support roll-back to previous environments and idempotent deployment it is necessary that a certain tagged docker image always refer to the same image.
However, docker hub allows images to be uploaded with the same tags as existing images (they override the old image). This completely breaks the idea of versioning your images.
We currently have work-arounds which involve our build scripts pulling all versions of an image and looking through the tags to check that an overwrite will not happen etc. but it feels like there has to be a better way.
If docker hub does not support this, is there a way to do docker deployment without docker hub?
The tag system has no way of preventing images been overwritten; you have to come up with your own processes to handle this (and h3nrik's answer is an example of this).
However, you could use the digest instead. In the new v2 of the registry, all images are given a checksum, known as a digest. If an image or any of its base layers change, the digest will change. So if you pull by digest, you can be absolutely certain that the contents of that image haven't changed over time and that the image hasn't been tampered with.
Pulling by digest looks like:
docker pull debian#sha256:f43366bc755696485050ce14e1429c481b6f0ca04505c4a3093dfdb4fafb899e
You should get the digest when you do a docker push.
Now, I agree that pulling by digest is a bit unwieldy, so you may want to set up a system that simply tracks digest and tag and can verify that the image hasn't changed.
In the future, this situation is likely to improve, with tools like Notary for signing images. Also, you may want to look at using labels to store metadata such as git hash or build number.
Assuming you have a local build system to build your Docker images: you could include the build number from your local build job in your tag. With that you assure your requirement:
... it is necessary that a certain tagged docker image always refer to the same image.
When your local build automatically pushes to docker hub it is assured that each push pushes an image with a unique tag.