Suppose I have a Dockerfile with the following contents:
FROM debian:stable-slim
RUN echo "Hello world"
If debian:stable-slim is not present on my local machine, docker build will automatically pull it from Docker Hub. But what about updates to that image? Will docker build perpetually continue to use the initial image download unless I delete it or include --pull?
No it will not automatically update, not unless you tell it not to use the cache (or the cache gets invalidated in some other way).
So you will indeed keep using the initial image.
Related
I'm trying to deploy a docker image that is an asp.net core (.NET6) WebApi to ssh server.
I know the command for transferring the image file is:
docker save <my_image_namee> | ssh -C user#address docker load
Is it possible to execute this command within the Dockerfile right after building the image?
A Dockerfile can never run commands on the host, push its own image, save its output to a file, or anything else. The only thing it's possible to do in a Dockerfile is specify the commands needed to build the image within its isolated environment.
So, for example, in your Dockerfile you can't specify the image name that will be used (or its tag), or forcibly push something to a registry, or the complex docker save | ssh sequence you show. There's no option in the Dockerfile to do it.
You must run this as two separate commands using pretty much the syntax you show as your second command. If the two systems are on a shared network, a better approach would be to set up a registry server of some sort and docker push the image there; the docker save...docker load sequence isn't usually a preferred option, unless the two systems are on physically isolated networks. Whatever you need to do after you build the image, you could also consider asking your continuous-integration system to do it for you to avoid the manual step.
I'm in low cost project that we send to container registry (DigitalOcean) only latest image.
But all time, after running:
docker build .
Is generating the same digest, every time.
This is my script for build:
docker build .
docker tag {image}:latest registry.digitalocean.com/{company}/{image}:latest;
docker push registry.digitalocean.com/{company}/{image}
I tried:
BUILD_VERSION=`date '+%s'`;
docker build -t {image}:"$NOW" -t {image}:latest .
docker tag {image}:latest registry.digitalocean.com/{company}/{image}:latest;
docker push registry.digitalocean.com/{company}/{image}
but not worked.
Editing my answer, what David said is correct - the push with out the tag should pick up latest tag.
If you provide what you have in your local repository and the output of the above commands, it would shed more light to your problem.
Edit 2:
I think I have figured out on why:
Is generating the same digest, every time.
This means, although you are running your docker build - there has been no change to the underlying artifacts which are being packaged into the image and hence it results into the same digest.
Sometimes layers are cached but there are changes that aren't detected so you can delete the image or use 'docker system prune' to force clearing cache here
I have to take a Docker image from a vendor site and then push the image into the private repository (Artifactory). This way the CI/CD pipeline can retrieve the image from the private repository and deploy the image.
What is the best way to achieve it, do I need to recreate the image?
steps:
take a pull of the base docker image from vendor.
create new folder for your new docker image.
create a Dockerfile.
write your base docker image.
do the changes inside this folder.
build new docker image using cmd.
push the image into docker hub.
refer this (not exactly according to your need, but this helps): https://www.howtoforge.com/tutorial/how-to-create-docker-images-with-dockerfile/
for cmd and Dockerfile changes, refer docker office doc site
I believe its a tar or zip file that they have given you by docker save and docker export.
You can perform below operations.
1. Perform docker load < file.tar - You will get the image name that's loaded. Note down the name.
1. Download the tar or zip file to your local.
2. Perform cat file.tar | docker import image_name_that_you_noted_above
3. You are good to use the image now. tag it to your repo and push, or directly run using docker run
When building a docker image you normally use docker build ..
But I've found that you can specify --pull, so the whole command would look like docker build --pull .
I'm not sure about the purpose of --pull. Docker's official documentation says "Always attempt to pull a newer version of the image", and I'm not sure what this means in this context.
You use docker build to build a new image, and eventually publish it somewhere to a container registry. Why would you want to pull something that doesn't exist yet?
it will pull the latest version of any base image(s) instead of reusing whatever you already have tagged locally
take for instance an image based on a moving tag (such as ubuntu:bionic). upstream makes changes and rebuilds this periodically but you might have a months old image locally. docker will happily build against the old base. --pull will pull as a side effect so you build against the latest base image
it's ~usually a best practice to use it to get upstream security fixes as soon as possible (instead of using stale, potentially vulnerable images). though you have to trade off breaking changes (and if you use immutable tags then it doesn't make a difference)
Docker allows passing the --pull flag to docker build, e.g. docker build . --pull -t myimage. This is the recommended way to ensure that the build always uses the latest container image despite the version available locally. However one additional point worth mentioning:
To ensure that your build is completely rebuilt, including checking the base image for updates, use the following options when building:
--no-cache - This will force rebuilding of layers already available.
The full command will therefore look like this:
docker build . --pull --no-cache --tag myimage:version
The same options are available for docker-compose:
docker-compose build --no-cache --pull
Simple answer. docker build is used to build from a local dockerfile. docker pull is used to pull from docker hub. If you use docker build without a docker file it throws an error.
When you specify --pull or :latest docker will try to download the newest version (if any)
Basically, if you add --pull, it will try to pull the newest version each time it is run.
I've met the case where Dockerfile looks like this:
FROM image with fully-configured server (without application)
COPY war created locally by IntelliJ inside server in Docker image
Basically every time when I'm starting container with this Dockerfile, Docker creates new image. Because this .war file is changing often (this is the whole purpose of using Docker here - for easy deploying .war images during development), I've a lot of not used images with older versions of this application. This causes space on disk problems and I have to manually prune all deprecated images.
Is there any way to disable Docker caching? I'm using a set of servers connected by docker-compose file, so maybe it can somehow manage those images to automatically remove them when it is not needed anymore?
docker build has --no-cache parameter, but it only invalidates cache for every layer (every command is always executed, but still saved inside images/layers repository). Also --force-rm is not working for me.
as Docker documentation says, if the file change on every docker build the cache will be ignored because the checksum file change, maybe you have to remove the COPY command from the Dockerfile and use a VOLUME and copy the war file on every docker run to ensure that war will change on every start