How do you add items to .dockerignore?

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I'm not able to find many examples of what a .dockerignore file should look like.

Using puppet to install a few packages on a docker container causes the image to explode from 600MB to 3GB. I'm trying to use a .dockerignore file to keep the size to a minumum

$ cat Dockerfile  
FROM centos:centos6

#Work around selinux problem on cent images
RUN yum install -y --enablerepo=centosplus libselinux-devel

RUN yum install -y wget git tar openssh-server; yum -y clean all

Add Puppetfile / 
RUN librarian-puppet install
RUN puppet apply --modulepath=/modules -e "class { 'buildslave': jenkins_slave => true,}"
RUN librarian-puppet clean

If I run docker images --tree I can see that the image instantlly grows by several GB

$ docker images --tree
                ├─e289570b5555 Virtual Size: 387.7 MB
                │ └─a7646acf90d0 Virtual Size: 442.5 MB
                │   └─d7bc6e1fbe43 Virtual Size: 442.5 MB
                │     └─772e6b204e3b Virtual Size: 627.5 MB
                │       └─599a7b5226f4 Virtual Size: 627.5 MB
                │         └─9fbffccda8bd Virtual Size: 2.943 GB
                │           └─ee46af013f6b Virtual Size: 2.943 GB
                │             └─3e4fe065fd07 Virtual Size: 2.943 GB
                │               └─de9ec3eba39e Virtual Size: 2.943 GB
                │                 └─31cba2716a12 Virtual Size: 2.943 GB
                │                   └─52cbc742d3c4 Virtual Size: 2.943 GB
                │                     └─9a857380258c Virtual Size: 2.943 GB
                │                       └─c6d87a343807 Virtual Size: 2.964 GB
                │                         └─f664124e0080 Virtual Size: 2.964 GB
                │                           └─e6cc212038b9 Virtual Size: 2.964 GB Tags: foo/jenkins-centos6-buildslave:latest

I believe the reason that the image grows so large, is because librarian-puppet clones a puppet module to /modules which breaks the build cache

I've tried the following .dockerignore files with no luck.

$ cat .dockerignore

Is this the correct syntax for a .dockerignore file? Are there any other ways to prevent these containers from growing so large?

Additional information:

.dockerignore is to prevent files from being added to the initial build context that is sent to the docker daemon when you do docker build, it doesn't create a global rule for excluding files from being created in all images generated by a Dockerfile.

It's important to note that each RUN statement will generate a new image, with the parent of that image being the image generated by the Dockerfile statement above it. Try collapsing your RUN statements into a single one to reduce image size:

RUN librarian-puppet install &&\
 puppet apply --modulepath=/modules -e "class { 'buildslave': jenkins_slave => true,}" &&\
 librarian-puppet clean

Leveraging the dockerignore File to Create Smaller Images, For this article, we will go ahead and add a .dockerignore file to one of my In the above, we have some clearly specified items such as docs/� .dockerignore must be in the current folder . like ./dockerignore. If you have a Dockerfile in a subfolder for example ./build/Dockerfile you can still build the image specifying where is the Dockerfile and which is the context: $

The format of the .dockerignore should be equal to the one of .gitignore. See a sample file and the docker documentation.

The file should be a list of exclusion patterns (relative to the path of the .dockerignore file) separated by a newline.

So you should try the following .dockerignore:


The / at the beginning may have been the mistake, as it will only be valid for the root directory of the file (but not for subdirectories, so maybe the recursive version without the / will do a better job instead).

Do not ignore .dockerignore (it's expensive and potentially , The .dockerignore file is the tool, that can help you to define the Docker command line tool talks with the Docker server and asks it to do things. Tip: The rule of thumb is not adding files to the build context, if you do not� Tip: The rule of thumb is not adding files to the build context, if you do not need them in your Docker image. The Docker context should be minimal and secret-free. The .dockerignore file. The .dockerignore file is the tool, that can help you to define the Docker build context you really need.

The .dockerignore file is similar to the .gitignore syntax. Here are some example rules:

# Ignore a file or directory in the context root named "modules"

# Ignore any files or directories within the subdirectory named "modules" 
# in the context root

# Ignore any files or directories in the context root beginning with "modules"

# Ignore any files or directories one level down from the context root named
# "modules"

# Ignore any files or directories at any level, including the context root, 
# named modules

# Ignore every file in the entire build context (see next rule for how this 
# could be used)

# Re-include the file or directory named "src" that may have been previously
# excluded. Note that you cannot re-include files in subdirectories that have 
# been previously excluded at a higher level

Note that "build context" is the directory you pass at the end of your build command, typically a . to indicate the current directory. This directory is packaged from the docker client, excluding any files you have ignored with .dockerignore, and sent to the docker daemon to perform the build. Even when the daemon is on the same host as your client, the build only works from this context and not directly from the folders.

There is only a single .dockerignore for a build, and it must be in the root of the build context. It will not work if it is in your home directory (assuming you build from a subdirectory), and it will not work from a subdirectory of your build context.

To test what is in your current build context and verify your .dockerignore file is behaving correctly, you can copy/paste the following (this assumes you do not have an image named test-context, it will be overwritten and then deleted if you do):

# create an image that includes the entire build context
docker build -t test-context -f - . <<EOF
FROM busybox
COPY . /context
WORKDIR /context
CMD find .

# run the image which executes the find command
docker container run --rm test-context

# cleanup the built image
docker image rm test-context

How to use your .dockerignore as a whitelist —, Using your .dockerignore as a whitelist can be an elegant option to avoid these mistakes and to reduce the effort to keep things up to date. files from the build context , add the following content to your .dockerignore :. .dockerignore est d'empêcher les fichiers d'être ajoutés au contexte de construction initial qui est envoyé au démon docker lorsque vous faites docker build, il ne crée pas de règle globale pour exclure les fichiers d'être créés dans toutes les images générées par un fichier Dockerfile.





would not work for me, docker kept on polluting the image with unnecessary files until I set it like this:


also works with:


Getting Control Of Your .dockerignore Files, The way .dockerignore is normally used, if you mistakenly put build files, like docker-compose.yml and .gitlab-ci.yml (to keep things private). If you just do the standard tutorials, everything works great in development. But, most of these tutorials don't cover the .dockerignore file. This file is very important and not having one becomes a problem when Docker runs the following line in the above Dockerfile: ```bash # Finally copy over rest of app. COPY . /app ```

A different way of doing it, creating a smaller image, is to run librarian-puppet in the host, not in Docker, so you don't end with librarian, ruby, gems,... installed in the image.

I ended with a 622MB image for jenkins slave using Puppet, and a 480MB image without Puppet.

Using .dockerignore files to build better Docker images, Dockerfile: FROM alpine:3.7 ADD . /var/opt/ CMD sleep infinity. Command to build the image: $ docker build -t testing . Get current image size:. For other items (files, directories) that do not require ADD’s tar auto-extraction capability, you should always use COPY. ENTRYPOINT. Dockerfile reference for the ENTRYPOINT instruction. The best use for ENTRYPOINT is to set the image’s main command, allowing that image to be run as though it was that command (and then use CMD as the

Hence, you need to put in the .dockerignore all the files not needed for your build Before the docker CLI sends the context to the docker daemon, it looks for a file named .dockerignore in the root directory of the context.

If you set up your list source as an Excel table, then all you need to do is add or remove items from the list, and Excel will automatically update any associated drop-downs for you. To add an item, go to the end of the list and type the new item. To remove an item, press Delete.

With the help of PHPStorm - Click right on project -> then you have an option ".i*" -> then select .dockerignore. It will ask you what type of project you have. I search for symfony PHP in my case. Then it will automatically create a template with all the files that need to be excluded. After this project seemed to be working more efficiently :)!

  • Thanks for your comment on my answer and this nice solution for the initial problem.
  • If those files are not needed to actually run the container, you can delete them as a final "cleanup" step in the Dockerfile. The resulting image be smaller, and you can also safely remove the intermediary build images to free disk space.
  • @Abe Voelker: I tried collapsing all the RUN statements to a single RUN statement, but the image size is the same. why is that?
  • Thanks for the answer. I updated the .dockerignore to the syntax suggested and rebuilt, it looks like the contianer is still growing to 3GB. Maybe I'm misunderstanding what the .dockerignore file is supposed to do.
  • @spuder Hm, I must confess, I haven't done anything with Puppet so far, so I don't understand every command up there. But for me, it doesn't look like a .dockerignore related problem. The behavior you noticed seems strange to me and like it shouldn't be like it is. So you'd make me curious to know where the problem is, too. So feel free to open up a new general question where the problem might be or even open up an issue at the docker git repository. Perhaps someone experienced a similar behavior and knows the answer. For some better information, try to get some log files from the build.
  • .dockerignore is not exactly equivalent to .gitignore. For example, .gitignore has rules for evaluating directories that are not followed by .dockerignore; e.g. /log in a .gitignore will ignore the log directory from the same directory that .gitignore is in, but .dockerignore doesn't process the leading / the same way and will not exclude it from the build context. So you won't necessarily be able to copy the rules directly from your .gitignore into your .dockerignore unmodified.
  • One thing that bit me is that the newlines need to be Unix newlines, not Windows ones. I had a .dockerignore-file edited on Windows sent over to a Unix system and docker kept "ignoring" my ignores until I converted it to Unix style newlines!
  • update - .dockerignore was added in docker 1.1.0. At the time of writing my ubuntu repo has docker 1.0.1 but the latest version of docker is 1.4.0. Not sure about the earlier implementations of the .dockerignore file but in docker 1.3.3 it doesn't support the trailing slashes on directory names meaning you can't differentiate between a filename and a directory name. If you add foo to the .dockerignore file, both files called foo and directories called foo would be ignored. As of 1.4.0, trailing slashes on directory names are supported, matching the .gitignore syntax.
  • This should be the accepted answer, this syntax seems to be the only one respected by docker on windows