mirror of
https://github.com/moby/moby.git
synced 2022-11-09 12:21:53 -05:00
3781cde61f
This way, images creators can set the exit signal their programs use. Signed-off-by: David Calavera <david.calavera@gmail.com>
1067 lines
40 KiB
Markdown
1067 lines
40 KiB
Markdown
<!--[metadata]>
|
||
+++
|
||
title = "Dockerfile reference"
|
||
description = "Dockerfiles use a simple DSL which allows you to automate the steps you would normally manually take to create an image."
|
||
keywords = ["builder, docker, Dockerfile, automation, image creation"]
|
||
[menu.main]
|
||
parent = "mn_reference"
|
||
+++
|
||
<![end-metadata]-->
|
||
|
||
# Dockerfile reference
|
||
|
||
Docker can build images automatically by reading the instructions from a
|
||
`Dockerfile`. A `Dockerfile` is a text document that contains all the commands a
|
||
user could call on the command line to assemble an image. Using `docker build`
|
||
users can create an automated build that executes several command-line
|
||
instructions in succession.
|
||
|
||
This page describes the commands you can use in a `Dockerfile`. When you are
|
||
done reading this page, refer to the [`Dockerfile` Best
|
||
Practices](/articles/dockerfile_best-practices) for a tip-oriented guide.
|
||
|
||
## Usage
|
||
|
||
The [`docker build`](/reference/commandline/build/) command builds an image from
|
||
a `Dockerfile` and a *context*. The build's context is the files at a specified
|
||
location `PATH` or `URL`. The `PATH` is a directory on your local filesystem.
|
||
The `URL` is a the location of a Git repository.
|
||
|
||
A context is processed recursively. So, a `PATH` includes any subdirectories and
|
||
the `URL` includes the repository and its submodules. A simple build command
|
||
that uses the current directory as context:
|
||
|
||
$ docker build .
|
||
Sending build context to Docker daemon 6.51 MB
|
||
...
|
||
|
||
The build is run by the Docker daemon, not by the CLI. The first thing a build
|
||
process does is send the entire context (recursively) to the daemon. In most
|
||
cases, it's best to start with an empty directory as context and keep your
|
||
Dockerfile in that directory. Add only the files needed for building the
|
||
Dockerfile.
|
||
|
||
>**Warning**: Do not use your root directory, `/`, as the `PATH` as it causes
|
||
>the build to transfer the entire contents of your hard drive to the Docker
|
||
>daemon.
|
||
|
||
To use a file in the build context, the `Dockerfile` refers to the file with
|
||
an instruction, for example, a `COPY` instruction. To increase the build's
|
||
performance, exclude files and directories by adding a `.dockerignore` file to
|
||
the context directory. For information about how to [create a `.dockerignore`
|
||
file](#dockerignore-file) see the documentation on this page.
|
||
|
||
Traditionally, the `Dockerfile` is called `Dockerfile` and located in the root
|
||
of the context. You use the `-f` flag with `docker build` to point to a Dockerfile
|
||
anywhere in your file system.
|
||
|
||
You can specify a repository and tag at which to save the new image if
|
||
the build succeeds:
|
||
|
||
$ docker build -t shykes/myapp .
|
||
|
||
The Docker daemon will run your steps one-by-one, committing the result
|
||
to a new image if necessary, before finally outputting the ID of your
|
||
new image. The Docker daemon will automatically clean up the context you
|
||
sent.
|
||
|
||
Note that each instruction is run independently, and causes a new image
|
||
to be created - so `RUN cd /tmp` will not have any effect on the next
|
||
instructions.
|
||
|
||
Whenever possible, Docker will re-use the intermediate images,
|
||
accelerating `docker build` significantly (indicated by `Using cache` -
|
||
see the [`Dockerfile` Best Practices
|
||
guide](/articles/dockerfile_best-practices/#build-cache) for more information):
|
||
|
||
$ docker build -t SvenDowideit/ambassador .
|
||
Uploading context 10.24 kB
|
||
Uploading context
|
||
Step 1 : FROM docker-ut
|
||
---> cbba202fe96b
|
||
Step 2 : MAINTAINER SvenDowideit@home.org.au
|
||
---> Using cache
|
||
---> 51182097be13
|
||
Step 3 : CMD env | grep _TCP= | sed 's/.*_PORT_\([0-9]*\)_TCP=tcp:\/\/\(.*\):\(.*\)/socat TCP4-LISTEN:\1,fork,reuseaddr TCP4:\2:\3 \&/' | sh && top
|
||
---> Using cache
|
||
---> 1a5ffc17324d
|
||
Successfully built 1a5ffc17324d
|
||
|
||
When you're done with your build, you're ready to look into [*Pushing a
|
||
repository to its registry*]( /userguide/dockerrepos/#contributing-to-docker-hub).
|
||
|
||
## Format
|
||
|
||
Here is the format of the `Dockerfile`:
|
||
|
||
# Comment
|
||
INSTRUCTION arguments
|
||
|
||
The Instruction is not case-sensitive, however convention is for them to
|
||
be UPPERCASE in order to distinguish them from arguments more easily.
|
||
|
||
Docker runs the instructions in a `Dockerfile` in order. **The
|
||
first instruction must be \`FROM\`** in order to specify the [*Base
|
||
Image*](/reference/glossary/#base-image) from which you are building.
|
||
|
||
Docker will treat lines that *begin* with `#` as a
|
||
comment. A `#` marker anywhere else in the line will
|
||
be treated as an argument. This allows statements like:
|
||
|
||
# Comment
|
||
RUN echo 'we are running some # of cool things'
|
||
|
||
Here is the set of instructions you can use in a `Dockerfile` for building
|
||
images.
|
||
|
||
### Environment replacement
|
||
|
||
Environment variables (declared with [the `ENV` statement](#env)) can also be
|
||
used in certain instructions as variables to be interpreted by the
|
||
`Dockerfile`. Escapes are also handled for including variable-like syntax
|
||
into a statement literally.
|
||
|
||
Environment variables are notated in the `Dockerfile` either with
|
||
`$variable_name` or `${variable_name}`. They are treated equivalently and the
|
||
brace syntax is typically used to address issues with variable names with no
|
||
whitespace, like `${foo}_bar`.
|
||
|
||
The `${variable_name}` syntax also supports a few of the standard `bash`
|
||
modifiers as specified below:
|
||
|
||
* `${variable:-word}` indicates that if `variable` is set then the result
|
||
will be that value. If `variable` is not set then `word` will be the result.
|
||
* `${variable:+word}` indicates that if `variable` is set then `word` will be
|
||
the result, otherwise the result is the empty string.
|
||
|
||
In all cases, `word` can be any string, including additional environment
|
||
variables.
|
||
|
||
Escaping is possible by adding a `\` before the variable: `\$foo` or `\${foo}`,
|
||
for example, will translate to `$foo` and `${foo}` literals respectively.
|
||
|
||
Example (parsed representation is displayed after the `#`):
|
||
|
||
FROM busybox
|
||
ENV foo /bar
|
||
WORKDIR ${foo} # WORKDIR /bar
|
||
ADD . $foo # ADD . /bar
|
||
COPY \$foo /quux # COPY $foo /quux
|
||
|
||
Environment variables are supported by the following list of instructions in
|
||
the `Dockerfile`:
|
||
|
||
* `ADD`
|
||
* `COPY`
|
||
* `ENV`
|
||
* `EXPOSE`
|
||
* `USER`
|
||
* `WORKDIR`
|
||
* `VOLUME`
|
||
* `STOPSIGNAL`
|
||
|
||
as well as:
|
||
|
||
* `ONBUILD` (when combined with one of the supported instructions above)
|
||
|
||
> **Note**:
|
||
> prior to 1.4, `ONBUILD` instructions did **NOT** support environment
|
||
> variable, even when combined with any of the instructions listed above.
|
||
|
||
Environment variable substitution will use the same value for each variable
|
||
throughout the entire command. In other words, in this example:
|
||
|
||
ENV abc=hello
|
||
ENV abc=bye def=$abc
|
||
ENV ghi=$abc
|
||
|
||
will result in `def` having a value of `hello`, not `bye`. However,
|
||
`ghi` will have a value of `bye` because it is not part of the same command
|
||
that set `abc` to `bye`.
|
||
|
||
### .dockerignore file
|
||
|
||
If a file named `.dockerignore` exists in the root of `PATH`, then Docker
|
||
interprets it as a newline-separated list of exclusion patterns. Docker excludes
|
||
files or directories relative to `PATH` that match these exclusion patterns. If
|
||
there are any `.dockerignore` files in `PATH` subdirectories, Docker treats
|
||
them as normal files.
|
||
|
||
Filepaths in `.dockerignore` are absolute with the current directory as the
|
||
root. Wildcards are allowed but the search is not recursive. Globbing (file name
|
||
expansion) is done using Go's
|
||
[filepath.Match](http://golang.org/pkg/path/filepath#Match) rules.
|
||
|
||
You can specify exceptions to exclusion rules. To do this, simply prefix a
|
||
pattern with an `!` (exclamation mark) in the same way you would in a
|
||
`.gitignore` file. Currently there is no support for regular expressions.
|
||
Formats like `[^temp*]` are ignored.
|
||
|
||
The following is an example `.dockerignore` file:
|
||
|
||
```
|
||
*/temp*
|
||
*/*/temp*
|
||
temp?
|
||
*.md
|
||
!LICENSE.md
|
||
```
|
||
|
||
This file causes the following build behavior:
|
||
|
||
| Rule | Behavior |
|
||
|----------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|
||
| `*/temp*` | Exclude all files with names starting with`temp` in any subdirectory below the root directory. For example, a file named`/somedir/temporary.txt` is ignored. |
|
||
| `*/*/temp*` | Exclude files starting with name `temp` from any subdirectory that is two levels below the root directory. For example, the file `/somedir/subdir/temporary.txt` is ignored. |
|
||
| `temp?` | Exclude the files that match the pattern in the root directory. For example, the files `tempa`, `tempb` in the root directory are ignored. |
|
||
| `*.md ` | Exclude all markdown files in the root directory. |
|
||
| `!LICENSE.md` | Exception to the Markdown files exclusion is this file, `LICENSE.md`, Include this file in the build. |
|
||
|
||
The placement of `!` exception rules influences the matching algorithm; the
|
||
last line of the `.dockerignore` that matches a particular file determines
|
||
whether it is included or excluded. In the above example, the `LICENSE.md` file
|
||
matches both the `*.md` and `!LICENSE.md` rule. If you reverse the lines in the
|
||
example:
|
||
|
||
```
|
||
*/temp*
|
||
*/*/temp*
|
||
temp?
|
||
!LICENSE.md
|
||
*.md
|
||
```
|
||
|
||
The build would exclude `LICENSE.md` because the last `*.md` rule adds all
|
||
Markdown files in the root directory back onto the ignore list. The
|
||
`!LICENSE.md` rule has no effect because the subsequent `*.md` rule overrides
|
||
it.
|
||
|
||
You can even use the `.dockerignore` file to ignore the `Dockerfile` and
|
||
`.dockerignore` files. This is useful if you are copying files from the root of
|
||
the build context into your new container but do not want to include the
|
||
`Dockerfile` or `.dockerignore` files (e.g. `ADD . /someDir/`).
|
||
|
||
|
||
## FROM
|
||
|
||
FROM <image>
|
||
|
||
Or
|
||
|
||
FROM <image>:<tag>
|
||
|
||
Or
|
||
|
||
FROM <image>@<digest>
|
||
|
||
The `FROM` instruction sets the [*Base Image*](/reference/glossary/#base-image)
|
||
for subsequent instructions. As such, a valid `Dockerfile` must have `FROM` as
|
||
its first instruction. The image can be any valid image – it is especially easy
|
||
to start by **pulling an image** from the [*Public Repositories*](
|
||
/userguide/dockerrepos).
|
||
|
||
`FROM` must be the first non-comment instruction in the `Dockerfile`.
|
||
|
||
`FROM` can appear multiple times within a single `Dockerfile` in order to create
|
||
multiple images. Simply make a note of the last image ID output by the commit
|
||
before each new `FROM` command.
|
||
|
||
The `tag` or `digest` values are optional. If you omit either of them, the builder
|
||
assumes a `latest` by default. The builder returns an error if it cannot match
|
||
the `tag` value.
|
||
|
||
## MAINTAINER
|
||
|
||
MAINTAINER <name>
|
||
|
||
The `MAINTAINER` instruction allows you to set the *Author* field of the
|
||
generated images.
|
||
|
||
## RUN
|
||
|
||
RUN has 2 forms:
|
||
|
||
- `RUN <command>` (the command is run in a shell - `/bin/sh -c` - *shell* form)
|
||
- `RUN ["executable", "param1", "param2"]` (*exec* form)
|
||
|
||
The `RUN` instruction will execute any commands in a new layer on top of the
|
||
current image and commit the results. The resulting committed image will be
|
||
used for the next step in the `Dockerfile`.
|
||
|
||
Layering `RUN` instructions and generating commits conforms to the core
|
||
concepts of Docker where commits are cheap and containers can be created from
|
||
any point in an image's history, much like source control.
|
||
|
||
The *exec* form makes it possible to avoid shell string munging, and to `RUN`
|
||
commands using a base image that does not contain `/bin/sh`.
|
||
|
||
> **Note**:
|
||
> To use a different shell, other than '/bin/sh', use the *exec* form
|
||
> passing in the desired shell. For example,
|
||
> `RUN ["/bin/bash", "-c", "echo hello"]`
|
||
|
||
> **Note**:
|
||
> The *exec* form is parsed as a JSON array, which means that
|
||
> you must use double-quotes (") around words not single-quotes (').
|
||
|
||
> **Note**:
|
||
> Unlike the *shell* form, the *exec* form does not invoke a command shell.
|
||
> This means that normal shell processing does not happen. For example,
|
||
> `RUN [ "echo", "$HOME" ]` will not do variable substitution on `$HOME`.
|
||
> If you want shell processing then either use the *shell* form or execute
|
||
> a shell directly, for example: `RUN [ "sh", "-c", "echo", "$HOME" ]`.
|
||
|
||
The cache for `RUN` instructions isn't invalidated automatically during
|
||
the next build. The cache for an instruction like
|
||
`RUN apt-get dist-upgrade -y` will be reused during the next build. The
|
||
cache for `RUN` instructions can be invalidated by using the `--no-cache`
|
||
flag, for example `docker build --no-cache`.
|
||
|
||
See the [`Dockerfile` Best Practices
|
||
guide](/articles/dockerfile_best-practices/#build-cache) for more information.
|
||
|
||
The cache for `RUN` instructions can be invalidated by `ADD` instructions. See
|
||
[below](#add) for details.
|
||
|
||
### Known issues (RUN)
|
||
|
||
- [Issue 783](https://github.com/docker/docker/issues/783) is about file
|
||
permissions problems that can occur when using the AUFS file system. You
|
||
might notice it during an attempt to `rm` a file, for example.
|
||
|
||
For systems that have recent aufs version (i.e., `dirperm1` mount option can
|
||
be set), docker will attempt to fix the issue automatically by mounting
|
||
the layers with `dirperm1` option. More details on `dirperm1` option can be
|
||
found at [`aufs` man page](http://aufs.sourceforge.net/aufs3/man.html)
|
||
|
||
If your system doesn't have support for `dirperm1`, the issue describes a workaround.
|
||
|
||
## CMD
|
||
|
||
The `CMD` instruction has three forms:
|
||
|
||
- `CMD ["executable","param1","param2"]` (*exec* form, this is the preferred form)
|
||
- `CMD ["param1","param2"]` (as *default parameters to ENTRYPOINT*)
|
||
- `CMD command param1 param2` (*shell* form)
|
||
|
||
There can only be one `CMD` instruction in a `Dockerfile`. If you list more than one `CMD`
|
||
then only the last `CMD` will take effect.
|
||
|
||
**The main purpose of a `CMD` is to provide defaults for an executing
|
||
container.** These defaults can include an executable, or they can omit
|
||
the executable, in which case you must specify an `ENTRYPOINT`
|
||
instruction as well.
|
||
|
||
> **Note**:
|
||
> If `CMD` is used to provide default arguments for the `ENTRYPOINT`
|
||
> instruction, both the `CMD` and `ENTRYPOINT` instructions should be specified
|
||
> with the JSON array format.
|
||
|
||
> **Note**:
|
||
> The *exec* form is parsed as a JSON array, which means that
|
||
> you must use double-quotes (") around words not single-quotes (').
|
||
|
||
> **Note**:
|
||
> Unlike the *shell* form, the *exec* form does not invoke a command shell.
|
||
> This means that normal shell processing does not happen. For example,
|
||
> `CMD [ "echo", "$HOME" ]` will not do variable substitution on `$HOME`.
|
||
> If you want shell processing then either use the *shell* form or execute
|
||
> a shell directly, for example: `CMD [ "sh", "-c", "echo", "$HOME" ]`.
|
||
|
||
When used in the shell or exec formats, the `CMD` instruction sets the command
|
||
to be executed when running the image.
|
||
|
||
If you use the *shell* form of the `CMD`, then the `<command>` will execute in
|
||
`/bin/sh -c`:
|
||
|
||
FROM ubuntu
|
||
CMD echo "This is a test." | wc -
|
||
|
||
If you want to **run your** `<command>` **without a shell** then you must
|
||
express the command as a JSON array and give the full path to the executable.
|
||
**This array form is the preferred format of `CMD`.** Any additional parameters
|
||
must be individually expressed as strings in the array:
|
||
|
||
FROM ubuntu
|
||
CMD ["/usr/bin/wc","--help"]
|
||
|
||
If you would like your container to run the same executable every time, then
|
||
you should consider using `ENTRYPOINT` in combination with `CMD`. See
|
||
[*ENTRYPOINT*](#entrypoint).
|
||
|
||
If the user specifies arguments to `docker run` then they will override the
|
||
default specified in `CMD`.
|
||
|
||
> **Note**:
|
||
> don't confuse `RUN` with `CMD`. `RUN` actually runs a command and commits
|
||
> the result; `CMD` does not execute anything at build time, but specifies
|
||
> the intended command for the image.
|
||
|
||
## LABEL
|
||
|
||
LABEL <key>=<value> <key>=<value> <key>=<value> ...
|
||
|
||
The `LABEL` instruction adds metadata to an image. A `LABEL` is a
|
||
key-value pair. To include spaces within a `LABEL` value, use quotes and
|
||
backslashes as you would in command-line parsing.
|
||
|
||
LABEL "com.example.vendor"="ACME Incorporated"
|
||
|
||
An image can have more than one label. To specify multiple labels, separate each
|
||
key-value pair with whitespace.
|
||
|
||
LABEL com.example.label-with-value="foo"
|
||
LABEL version="1.0"
|
||
LABEL description="This text illustrates \
|
||
that label-values can span multiple lines."
|
||
|
||
Docker recommends combining labels in a single `LABEL` instruction where
|
||
possible. Each `LABEL` instruction produces a new layer which can result in an
|
||
inefficient image if you use many labels. This example results in four image
|
||
layers.
|
||
|
||
LABEL multi.label1="value1" multi.label2="value2" other="value3"
|
||
|
||
Labels are additive including `LABEL`s in `FROM` images. As the system
|
||
encounters and then applies a new label, new `key`s override any previous labels
|
||
with identical keys.
|
||
|
||
To view an image's labels, use the `docker inspect` command.
|
||
|
||
"Labels": {
|
||
"com.example.vendor": "ACME Incorporated"
|
||
"com.example.label-with-value": "foo",
|
||
"version": "1.0",
|
||
"description": "This text illustrates that label-values can span multiple lines.",
|
||
"multi.label1": "value1",
|
||
"multi.label2": "value2",
|
||
"other": "value3"
|
||
},
|
||
|
||
## EXPOSE
|
||
|
||
EXPOSE <port> [<port>...]
|
||
|
||
The `EXPOSE` instructions informs Docker that the container will listen on the
|
||
specified network ports at runtime. Docker uses this information to interconnect
|
||
containers using links (see the [Docker User
|
||
Guide](/userguide/dockerlinks)) and to determine which ports to expose to the
|
||
host when [using the -P flag](/reference/run/#expose-incoming-ports).
|
||
|
||
> **Note**:
|
||
> `EXPOSE` doesn't define which ports can be exposed to the host or make ports
|
||
> accessible from the host by default. To expose ports to the host, at runtime,
|
||
> [use the `-p` flag](/userguide/dockerlinks) or
|
||
> [the -P flag](/reference/run/#expose-incoming-ports).
|
||
|
||
## ENV
|
||
|
||
ENV <key> <value>
|
||
ENV <key>=<value> ...
|
||
|
||
The `ENV` instruction sets the environment variable `<key>` to the value
|
||
`<value>`. This value will be in the environment of all "descendent" `Dockerfile`
|
||
commands and can be [replaced inline](#environment-replacement) in many as well.
|
||
|
||
The `ENV` instruction has two forms. The first form, `ENV <key> <value>`,
|
||
will set a single variable to a value. The entire string after the first
|
||
space will be treated as the `<value>` - including characters such as
|
||
spaces and quotes.
|
||
|
||
The second form, `ENV <key>=<value> ...`, allows for multiple variables to
|
||
be set at one time. Notice that the second form uses the equals sign (=)
|
||
in the syntax, while the first form does not. Like command line parsing,
|
||
quotes and backslashes can be used to include spaces within values.
|
||
|
||
For example:
|
||
|
||
ENV myName="John Doe" myDog=Rex\ The\ Dog \
|
||
myCat=fluffy
|
||
|
||
and
|
||
|
||
ENV myName John Doe
|
||
ENV myDog Rex The Dog
|
||
ENV myCat fluffy
|
||
|
||
will yield the same net results in the final container, but the first form
|
||
does it all in one layer.
|
||
|
||
The environment variables set using `ENV` will persist when a container is run
|
||
from the resulting image. You can view the values using `docker inspect`, and
|
||
change them using `docker run --env <key>=<value>`.
|
||
|
||
> **Note**:
|
||
> Environment persistence can cause unexpected effects. For example,
|
||
> setting `ENV DEBIAN_FRONTEND noninteractive` may confuse apt-get
|
||
> users on a Debian-based image. To set a value for a single command, use
|
||
> `RUN <key>=<value> <command>`.
|
||
|
||
## ADD
|
||
|
||
ADD has two forms:
|
||
|
||
- `ADD <src>... <dest>`
|
||
- `ADD ["<src>",... "<dest>"]` (this form is required for paths containing
|
||
whitespace)
|
||
|
||
The `ADD` instruction copies new files, directories or remote file URLs from `<src>`
|
||
and adds them to the filesystem of the container at the path `<dest>`.
|
||
|
||
Multiple `<src>` resource may be specified but if they are files or
|
||
directories then they must be relative to the source directory that is
|
||
being built (the context of the build).
|
||
|
||
Each `<src>` may contain wildcards and matching will be done using Go's
|
||
[filepath.Match](http://golang.org/pkg/path/filepath#Match) rules.
|
||
For most command line uses this should act as expected, for example:
|
||
|
||
ADD hom* /mydir/ # adds all files starting with "hom"
|
||
ADD hom?.txt /mydir/ # ? is replaced with any single character
|
||
|
||
The `<dest>` is an absolute path, or a path relative to `WORKDIR`, into which
|
||
the source will be copied inside the destination container.
|
||
|
||
ADD test aDir/ # adds "test" to `WORKDIR`/aDir/
|
||
|
||
All new files and directories are created with a UID and GID of 0.
|
||
|
||
In the case where `<src>` is a remote file URL, the destination will
|
||
have permissions of 600. If the remote file being retrieved has an HTTP
|
||
`Last-Modified` header, the timestamp from that header will be used
|
||
to set the `mtime` on the destination file. However, like any other file
|
||
processed during an `ADD`, `mtime` will not be included in the determination
|
||
of whether or not the file has changed and the cache should be updated.
|
||
|
||
> **Note**:
|
||
> If you build by passing a `Dockerfile` through STDIN (`docker
|
||
> build - < somefile`), there is no build context, so the `Dockerfile`
|
||
> can only contain a URL based `ADD` instruction. You can also pass a
|
||
> compressed archive through STDIN: (`docker build - < archive.tar.gz`),
|
||
> the `Dockerfile` at the root of the archive and the rest of the
|
||
> archive will get used at the context of the build.
|
||
|
||
> **Note**:
|
||
> If your URL files are protected using authentication, you
|
||
> will need to use `RUN wget`, `RUN curl` or use another tool from
|
||
> within the container as the `ADD` instruction does not support
|
||
> authentication.
|
||
|
||
> **Note**:
|
||
> The first encountered `ADD` instruction will invalidate the cache for all
|
||
> following instructions from the Dockerfile if the contents of `<src>` have
|
||
> changed. This includes invalidating the cache for `RUN` instructions.
|
||
> See the [`Dockerfile` Best Practices
|
||
guide](/articles/dockerfile_best-practices/#build-cache) for more information.
|
||
|
||
|
||
The copy obeys the following rules:
|
||
|
||
- The `<src>` path must be inside the *context* of the build;
|
||
you cannot `ADD ../something /something`, because the first step of a
|
||
`docker build` is to send the context directory (and subdirectories) to the
|
||
docker daemon.
|
||
|
||
- If `<src>` is a URL and `<dest>` does not end with a trailing slash, then a
|
||
file is downloaded from the URL and copied to `<dest>`.
|
||
|
||
- If `<src>` is a URL and `<dest>` does end with a trailing slash, then the
|
||
filename is inferred from the URL and the file is downloaded to
|
||
`<dest>/<filename>`. For instance, `ADD http://example.com/foobar /` would
|
||
create the file `/foobar`. The URL must have a nontrivial path so that an
|
||
appropriate filename can be discovered in this case (`http://example.com`
|
||
will not work).
|
||
|
||
- If `<src>` is a directory, the entire contents of the directory are copied,
|
||
including filesystem metadata.
|
||
> **Note**:
|
||
> The directory itself is not copied, just its contents.
|
||
|
||
- If `<src>` is a *local* tar archive in a recognized compression format
|
||
(identity, gzip, bzip2 or xz) then it is unpacked as a directory. Resources
|
||
from *remote* URLs are **not** decompressed. When a directory is copied or
|
||
unpacked, it has the same behavior as `tar -x`: the result is the union of:
|
||
|
||
1. Whatever existed at the destination path and
|
||
2. The contents of the source tree, with conflicts resolved in favor
|
||
of "2." on a file-by-file basis.
|
||
|
||
- If `<src>` is any other kind of file, it is copied individually along with
|
||
its metadata. In this case, if `<dest>` ends with a trailing slash `/`, it
|
||
will be considered a directory and the contents of `<src>` will be written
|
||
at `<dest>/base(<src>)`.
|
||
|
||
- If multiple `<src>` resources are specified, either directly or due to the
|
||
use of a wildcard, then `<dest>` must be a directory, and it must end with
|
||
a slash `/`.
|
||
|
||
- If `<dest>` does not end with a trailing slash, it will be considered a
|
||
regular file and the contents of `<src>` will be written at `<dest>`.
|
||
|
||
- If `<dest>` doesn't exist, it is created along with all missing directories
|
||
in its path.
|
||
|
||
## COPY
|
||
|
||
COPY has two forms:
|
||
|
||
- `COPY <src>... <dest>`
|
||
- `COPY ["<src>",... "<dest>"]` (this form is required for paths containing
|
||
whitespace)
|
||
|
||
The `COPY` instruction copies new files or directories from `<src>`
|
||
and adds them to the filesystem of the container at the path `<dest>`.
|
||
|
||
Multiple `<src>` resource may be specified but they must be relative
|
||
to the source directory that is being built (the context of the build).
|
||
|
||
Each `<src>` may contain wildcards and matching will be done using Go's
|
||
[filepath.Match](http://golang.org/pkg/path/filepath#Match) rules.
|
||
For most command line uses this should act as expected, for example:
|
||
|
||
COPY hom* /mydir/ # adds all files starting with "hom"
|
||
COPY hom?.txt /mydir/ # ? is replaced with any single character
|
||
|
||
The `<dest>` is an absolute path, or a path relative to `WORKDIR`, into which
|
||
the source will be copied inside the destination container.
|
||
|
||
COPY test aDir/ # adds "test" to `WORKDIR`/aDir/
|
||
|
||
All new files and directories are created with a UID and GID of 0.
|
||
|
||
> **Note**:
|
||
> If you build using STDIN (`docker build - < somefile`), there is no
|
||
> build context, so `COPY` can't be used.
|
||
|
||
The copy obeys the following rules:
|
||
|
||
- The `<src>` path must be inside the *context* of the build;
|
||
you cannot `COPY ../something /something`, because the first step of a
|
||
`docker build` is to send the context directory (and subdirectories) to the
|
||
docker daemon.
|
||
|
||
- If `<src>` is a directory, the entire contents of the directory are copied,
|
||
including filesystem metadata.
|
||
> **Note**:
|
||
> The directory itself is not copied, just its contents.
|
||
|
||
- If `<src>` is any other kind of file, it is copied individually along with
|
||
its metadata. In this case, if `<dest>` ends with a trailing slash `/`, it
|
||
will be considered a directory and the contents of `<src>` will be written
|
||
at `<dest>/base(<src>)`.
|
||
|
||
- If multiple `<src>` resources are specified, either directly or due to the
|
||
use of a wildcard, then `<dest>` must be a directory, and it must end with
|
||
a slash `/`.
|
||
|
||
- If `<dest>` does not end with a trailing slash, it will be considered a
|
||
regular file and the contents of `<src>` will be written at `<dest>`.
|
||
|
||
- If `<dest>` doesn't exist, it is created along with all missing directories
|
||
in its path.
|
||
|
||
## ENTRYPOINT
|
||
|
||
ENTRYPOINT has two forms:
|
||
|
||
- `ENTRYPOINT ["executable", "param1", "param2"]`
|
||
(the preferred *exec* form)
|
||
- `ENTRYPOINT command param1 param2`
|
||
(*shell* form)
|
||
|
||
An `ENTRYPOINT` allows you to configure a container that will run as an executable.
|
||
|
||
For example, the following will start nginx with its default content, listening
|
||
on port 80:
|
||
|
||
docker run -i -t --rm -p 80:80 nginx
|
||
|
||
Command line arguments to `docker run <image>` will be appended after all
|
||
elements in an *exec* form `ENTRYPOINT`, and will override all elements specified
|
||
using `CMD`.
|
||
This allows arguments to be passed to the entry point, i.e., `docker run <image> -d`
|
||
will pass the `-d` argument to the entry point.
|
||
You can override the `ENTRYPOINT` instruction using the `docker run --entrypoint`
|
||
flag.
|
||
|
||
The *shell* form prevents any `CMD` or `run` command line arguments from being
|
||
used, but has the disadvantage that your `ENTRYPOINT` will be started as a
|
||
subcommand of `/bin/sh -c`, which does not pass signals.
|
||
This means that the executable will not be the container's `PID 1` - and
|
||
will _not_ receive Unix signals - so your executable will not receive a
|
||
`SIGTERM` from `docker stop <container>`.
|
||
|
||
Only the last `ENTRYPOINT` instruction in the `Dockerfile` will have an effect.
|
||
|
||
### Exec form ENTRYPOINT example
|
||
|
||
You can use the *exec* form of `ENTRYPOINT` to set fairly stable default commands
|
||
and arguments and then use either form of `CMD` to set additional defaults that
|
||
are more likely to be changed.
|
||
|
||
FROM ubuntu
|
||
ENTRYPOINT ["top", "-b"]
|
||
CMD ["-c"]
|
||
|
||
When you run the container, you can see that `top` is the only process:
|
||
|
||
$ docker run -it --rm --name test top -H
|
||
top - 08:25:00 up 7:27, 0 users, load average: 0.00, 0.01, 0.05
|
||
Threads: 1 total, 1 running, 0 sleeping, 0 stopped, 0 zombie
|
||
%Cpu(s): 0.1 us, 0.1 sy, 0.0 ni, 99.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
|
||
KiB Mem: 2056668 total, 1616832 used, 439836 free, 99352 buffers
|
||
KiB Swap: 1441840 total, 0 used, 1441840 free. 1324440 cached Mem
|
||
|
||
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
|
||
1 root 20 0 19744 2336 2080 R 0.0 0.1 0:00.04 top
|
||
|
||
To examine the result further, you can use `docker exec`:
|
||
|
||
$ docker exec -it test ps aux
|
||
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
|
||
root 1 2.6 0.1 19752 2352 ? Ss+ 08:24 0:00 top -b -H
|
||
root 7 0.0 0.1 15572 2164 ? R+ 08:25 0:00 ps aux
|
||
|
||
And you can gracefully request `top` to shut down using `docker stop test`.
|
||
|
||
The following `Dockerfile` shows using the `ENTRYPOINT` to run Apache in the
|
||
foreground (i.e., as `PID 1`):
|
||
|
||
```
|
||
FROM debian:stable
|
||
RUN apt-get update && apt-get install -y --force-yes apache2
|
||
EXPOSE 80 443
|
||
VOLUME ["/var/www", "/var/log/apache2", "/etc/apache2"]
|
||
ENTRYPOINT ["/usr/sbin/apache2ctl", "-D", "FOREGROUND"]
|
||
```
|
||
|
||
If you need to write a starter script for a single executable, you can ensure that
|
||
the final executable receives the Unix signals by using `exec` and `gosu`
|
||
commands:
|
||
|
||
```bash
|
||
#!/bin/bash
|
||
set -e
|
||
|
||
if [ "$1" = 'postgres' ]; then
|
||
chown -R postgres "$PGDATA"
|
||
|
||
if [ -z "$(ls -A "$PGDATA")" ]; then
|
||
gosu postgres initdb
|
||
fi
|
||
|
||
exec gosu postgres "$@"
|
||
fi
|
||
|
||
exec "$@"
|
||
```
|
||
|
||
Lastly, if you need to do some extra cleanup (or communicate with other containers)
|
||
on shutdown, or are co-ordinating more than one executable, you may need to ensure
|
||
that the `ENTRYPOINT` script receives the Unix signals, passes them on, and then
|
||
does some more work:
|
||
|
||
```
|
||
#!/bin/sh
|
||
# Note: I've written this using sh so it works in the busybox container too
|
||
|
||
# USE the trap if you need to also do manual cleanup after the service is stopped,
|
||
# or need to start multiple services in the one container
|
||
trap "echo TRAPed signal" HUP INT QUIT KILL TERM
|
||
|
||
# start service in background here
|
||
/usr/sbin/apachectl start
|
||
|
||
echo "[hit enter key to exit] or run 'docker stop <container>'"
|
||
read
|
||
|
||
# stop service and clean up here
|
||
echo "stopping apache"
|
||
/usr/sbin/apachectl stop
|
||
|
||
echo "exited $0"
|
||
```
|
||
|
||
If you run this image with `docker run -it --rm -p 80:80 --name test apache`,
|
||
you can then examine the container's processes with `docker exec`, or `docker top`,
|
||
and then ask the script to stop Apache:
|
||
|
||
```bash
|
||
$ docker exec -it test ps aux
|
||
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
|
||
root 1 0.1 0.0 4448 692 ? Ss+ 00:42 0:00 /bin/sh /run.sh 123 cmd cmd2
|
||
root 19 0.0 0.2 71304 4440 ? Ss 00:42 0:00 /usr/sbin/apache2 -k start
|
||
www-data 20 0.2 0.2 360468 6004 ? Sl 00:42 0:00 /usr/sbin/apache2 -k start
|
||
www-data 21 0.2 0.2 360468 6000 ? Sl 00:42 0:00 /usr/sbin/apache2 -k start
|
||
root 81 0.0 0.1 15572 2140 ? R+ 00:44 0:00 ps aux
|
||
$ docker top test
|
||
PID USER COMMAND
|
||
10035 root {run.sh} /bin/sh /run.sh 123 cmd cmd2
|
||
10054 root /usr/sbin/apache2 -k start
|
||
10055 33 /usr/sbin/apache2 -k start
|
||
10056 33 /usr/sbin/apache2 -k start
|
||
$ /usr/bin/time docker stop test
|
||
test
|
||
real 0m 0.27s
|
||
user 0m 0.03s
|
||
sys 0m 0.03s
|
||
```
|
||
|
||
> **Note:** you can over ride the `ENTRYPOINT` setting using `--entrypoint`,
|
||
> but this can only set the binary to *exec* (no `sh -c` will be used).
|
||
|
||
> **Note**:
|
||
> The *exec* form is parsed as a JSON array, which means that
|
||
> you must use double-quotes (") around words not single-quotes (').
|
||
|
||
> **Note**:
|
||
> Unlike the *shell* form, the *exec* form does not invoke a command shell.
|
||
> This means that normal shell processing does not happen. For example,
|
||
> `ENTRYPOINT [ "echo", "$HOME" ]` will not do variable substitution on `$HOME`.
|
||
> If you want shell processing then either use the *shell* form or execute
|
||
> a shell directly, for example: `ENTRYPOINT [ "sh", "-c", "echo", "$HOME" ]`.
|
||
> Variables that are defined in the `Dockerfile`using `ENV`, will be substituted by
|
||
> the `Dockerfile` parser.
|
||
|
||
### Shell form ENTRYPOINT example
|
||
|
||
You can specify a plain string for the `ENTRYPOINT` and it will execute in `/bin/sh -c`.
|
||
This form will use shell processing to substitute shell environment variables,
|
||
and will ignore any `CMD` or `docker run` command line arguments.
|
||
To ensure that `docker stop` will signal any long running `ENTRYPOINT` executable
|
||
correctly, you need to remember to start it with `exec`:
|
||
|
||
FROM ubuntu
|
||
ENTRYPOINT exec top -b
|
||
|
||
When you run this image, you'll see the single `PID 1` process:
|
||
|
||
$ docker run -it --rm --name test top
|
||
Mem: 1704520K used, 352148K free, 0K shrd, 0K buff, 140368121167873K cached
|
||
CPU: 5% usr 0% sys 0% nic 94% idle 0% io 0% irq 0% sirq
|
||
Load average: 0.08 0.03 0.05 2/98 6
|
||
PID PPID USER STAT VSZ %VSZ %CPU COMMAND
|
||
1 0 root R 3164 0% 0% top -b
|
||
|
||
Which will exit cleanly on `docker stop`:
|
||
|
||
$ /usr/bin/time docker stop test
|
||
test
|
||
real 0m 0.20s
|
||
user 0m 0.02s
|
||
sys 0m 0.04s
|
||
|
||
If you forget to add `exec` to the beginning of your `ENTRYPOINT`:
|
||
|
||
FROM ubuntu
|
||
ENTRYPOINT top -b
|
||
CMD --ignored-param1
|
||
|
||
You can then run it (giving it a name for the next step):
|
||
|
||
$ docker run -it --name test top --ignored-param2
|
||
Mem: 1704184K used, 352484K free, 0K shrd, 0K buff, 140621524238337K cached
|
||
CPU: 9% usr 2% sys 0% nic 88% idle 0% io 0% irq 0% sirq
|
||
Load average: 0.01 0.02 0.05 2/101 7
|
||
PID PPID USER STAT VSZ %VSZ %CPU COMMAND
|
||
1 0 root S 3168 0% 0% /bin/sh -c top -b cmd cmd2
|
||
7 1 root R 3164 0% 0% top -b
|
||
|
||
You can see from the output of `top` that the specified `ENTRYPOINT` is not `PID 1`.
|
||
|
||
If you then run `docker stop test`, the container will not exit cleanly - the
|
||
`stop` command will be forced to send a `SIGKILL` after the timeout:
|
||
|
||
$ docker exec -it test ps aux
|
||
PID USER COMMAND
|
||
1 root /bin/sh -c top -b cmd cmd2
|
||
7 root top -b
|
||
8 root ps aux
|
||
$ /usr/bin/time docker stop test
|
||
test
|
||
real 0m 10.19s
|
||
user 0m 0.04s
|
||
sys 0m 0.03s
|
||
|
||
## VOLUME
|
||
|
||
VOLUME ["/data"]
|
||
|
||
The `VOLUME` instruction creates a mount point with the specified name
|
||
and marks it as holding externally mounted volumes from native host or other
|
||
containers. The value can be a JSON array, `VOLUME ["/var/log/"]`, or a plain
|
||
string with multiple arguments, such as `VOLUME /var/log` or `VOLUME /var/log
|
||
/var/db`. For more information/examples and mounting instructions via the
|
||
Docker client, refer to
|
||
[*Share Directories via Volumes*](/userguide/dockervolumes/#mount-a-host-directory-as-a-data-volume)
|
||
documentation.
|
||
|
||
The `docker run` command initializes the newly created volume with any data
|
||
that exists at the specified location within the base image. For example,
|
||
consider the following Dockerfile snippet:
|
||
|
||
FROM ubuntu
|
||
RUN mkdir /myvol
|
||
RUN echo "hello world" > /myvol/greeting
|
||
VOLUME /myvol
|
||
|
||
This Dockerfile results in an image that causes `docker run`, to
|
||
create a new mount point at `/myvol` and copy the `greeting` file
|
||
into the newly created volume.
|
||
|
||
> **Note**:
|
||
> If any build steps change the data within the volume after it has been
|
||
> declared, those changes will be discarded.
|
||
|
||
> **Note**:
|
||
> The list is parsed as a JSON array, which means that
|
||
> you must use double-quotes (") around words not single-quotes (').
|
||
|
||
## USER
|
||
|
||
USER daemon
|
||
|
||
The `USER` instruction sets the user name or UID to use when running the image
|
||
and for any `RUN`, `CMD` and `ENTRYPOINT` instructions that follow it in the
|
||
`Dockerfile`.
|
||
|
||
## WORKDIR
|
||
|
||
WORKDIR /path/to/workdir
|
||
|
||
The `WORKDIR` instruction sets the working directory for any `RUN`, `CMD`,
|
||
`ENTRYPOINT`, `COPY` and `ADD` instructions that follow it in the `Dockerfile`.
|
||
|
||
It can be used multiple times in the one `Dockerfile`. If a relative path
|
||
is provided, it will be relative to the path of the previous `WORKDIR`
|
||
instruction. For example:
|
||
|
||
WORKDIR /a
|
||
WORKDIR b
|
||
WORKDIR c
|
||
RUN pwd
|
||
|
||
The output of the final `pwd` command in this `Dockerfile` would be
|
||
`/a/b/c`.
|
||
|
||
The `WORKDIR` instruction can resolve environment variables previously set using
|
||
`ENV`. You can only use environment variables explicitly set in the `Dockerfile`.
|
||
For example:
|
||
|
||
ENV DIRPATH /path
|
||
WORKDIR $DIRPATH/$DIRNAME
|
||
RUN pwd
|
||
|
||
The output of the final `pwd` command in this `Dockerfile` would be
|
||
`/path/$DIRNAME`
|
||
|
||
## ONBUILD
|
||
|
||
ONBUILD [INSTRUCTION]
|
||
|
||
The `ONBUILD` instruction adds to the image a *trigger* instruction to
|
||
be executed at a later time, when the image is used as the base for
|
||
another build. The trigger will be executed in the context of the
|
||
downstream build, as if it had been inserted immediately after the
|
||
`FROM` instruction in the downstream `Dockerfile`.
|
||
|
||
Any build instruction can be registered as a trigger.
|
||
|
||
This is useful if you are building an image which will be used as a base
|
||
to build other images, for example an application build environment or a
|
||
daemon which may be customized with user-specific configuration.
|
||
|
||
For example, if your image is a reusable Python application builder, it
|
||
will require application source code to be added in a particular
|
||
directory, and it might require a build script to be called *after*
|
||
that. You can't just call `ADD` and `RUN` now, because you don't yet
|
||
have access to the application source code, and it will be different for
|
||
each application build. You could simply provide application developers
|
||
with a boilerplate `Dockerfile` to copy-paste into their application, but
|
||
that is inefficient, error-prone and difficult to update because it
|
||
mixes with application-specific code.
|
||
|
||
The solution is to use `ONBUILD` to register advance instructions to
|
||
run later, during the next build stage.
|
||
|
||
Here's how it works:
|
||
|
||
1. When it encounters an `ONBUILD` instruction, the builder adds a
|
||
trigger to the metadata of the image being built. The instruction
|
||
does not otherwise affect the current build.
|
||
2. At the end of the build, a list of all triggers is stored in the
|
||
image manifest, under the key `OnBuild`. They can be inspected with
|
||
the `docker inspect` command.
|
||
3. Later the image may be used as a base for a new build, using the
|
||
`FROM` instruction. As part of processing the `FROM` instruction,
|
||
the downstream builder looks for `ONBUILD` triggers, and executes
|
||
them in the same order they were registered. If any of the triggers
|
||
fail, the `FROM` instruction is aborted which in turn causes the
|
||
build to fail. If all triggers succeed, the `FROM` instruction
|
||
completes and the build continues as usual.
|
||
4. Triggers are cleared from the final image after being executed. In
|
||
other words they are not inherited by "grand-children" builds.
|
||
|
||
For example you might add something like this:
|
||
|
||
[...]
|
||
ONBUILD ADD . /app/src
|
||
ONBUILD RUN /usr/local/bin/python-build --dir /app/src
|
||
[...]
|
||
|
||
> **Warning**: Chaining `ONBUILD` instructions using `ONBUILD ONBUILD` isn't allowed.
|
||
|
||
> **Warning**: The `ONBUILD` instruction may not trigger `FROM` or `MAINTAINER` instructions.
|
||
|
||
## STOPSIGNAL
|
||
|
||
STOPSIGNAL signal
|
||
|
||
The `STOPSIGNAL` instruction sets the system call signal that will be sent to the container to exit.
|
||
This signal can be a valid unsigned number that matches a position in the kernel's syscall table, for instance 9,
|
||
or a signal name in the format SIGNAME, for instance SIGKILL.
|
||
|
||
## Dockerfile examples
|
||
|
||
# Nginx
|
||
#
|
||
# VERSION 0.0.1
|
||
|
||
FROM ubuntu
|
||
MAINTAINER Victor Vieux <victor@docker.com>
|
||
|
||
LABEL Description="This image is used to start the foobar executable" Vendor="ACME Products" Version="1.0"
|
||
RUN apt-get update && apt-get install -y inotify-tools nginx apache2 openssh-server
|
||
|
||
# Firefox over VNC
|
||
#
|
||
# VERSION 0.3
|
||
|
||
FROM ubuntu
|
||
|
||
# Install vnc, xvfb in order to create a 'fake' display and firefox
|
||
RUN apt-get update && apt-get install -y x11vnc xvfb firefox
|
||
RUN mkdir ~/.vnc
|
||
# Setup a password
|
||
RUN x11vnc -storepasswd 1234 ~/.vnc/passwd
|
||
# Autostart firefox (might not be the best way, but it does the trick)
|
||
RUN bash -c 'echo "firefox" >> /.bashrc'
|
||
|
||
EXPOSE 5900
|
||
CMD ["x11vnc", "-forever", "-usepw", "-create"]
|
||
|
||
# Multiple images example
|
||
#
|
||
# VERSION 0.1
|
||
|
||
FROM ubuntu
|
||
RUN echo foo > bar
|
||
# Will output something like ===> 907ad6c2736f
|
||
|
||
FROM ubuntu
|
||
RUN echo moo > oink
|
||
# Will output something like ===> 695d7793cbe4
|
||
|
||
# You᾿ll now have two images, 907ad6c2736f with /bar, and 695d7793cbe4 with
|
||
# /oink.
|
||
|