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Update best practices for entrypoint.

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Despite being wrong we are kinda calling our users dumb, I feel it is a bit
demeaning. As well as just wrong.

Docker-DCO-1.1-Signed-off-by: Jessie Frazelle <princess@docker.com> (github: jfrazelle)

Docker-DCO-1.1-Signed-off-by: Jessie Frazelle <hugs@docker.com> (github: jfrazelle)
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Jessica Frazelle 2015-01-30 15:49:43 -08:00 committed by Sven Dowideit
parent bac58e9711
commit 6009f2eac4
1 changed files with 11 additions and 17 deletions
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28
docs/sources/articles/dockerfile_best-practices.md
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@ -291,28 +291,22 @@ auto-extraction capability, you should always use `COPY`.
### [`ENTRYPOINT`](https://docs.docker.com/reference/builder/#entrypoint)
The best use for `ENTRYPOINT` is as a helper script. Using `ENTRYPOINT` for
other tasks can make your code harder to understand. For example,
The best use for `ENTRYPOINT` is as the main command.
....docker run -it official-image bash
Let's start with an example, of an image for the cli tool `s3cmd`:
is much easier to understand than
ENTRYPOINT ["s3cmd"]
CMD ["--help"]
....docker run -it --entrypoint bash official-image -i
Now people who consume this image can easily run commands via syntax like the
following:
This is especially true for new Docker users, who might naturally assume the
above command will work fine. In cases where an image uses `ENTRYPOINT` for
anything other than just a wrapper script, the command will fail and the
beginning user will then be forced to learn about `ENTRYPOINT` and
`--entrypoint`.
$ docker run scmd ls s3://mybucket
In order to avoid a situation where commands are run without clear visibility
to the user, make sure your script ends with something like `exec "$@"` (see
[the exec builtin command](http://wiki.bash-hackers.org/commands/builtin/exec)).
After the entrypoint completes, the script will transparently bootstrap the command
invoked by the user, making what has been run clear to the user (for example,
`docker run -it mysql mysqld --some --flags` will transparently run
`mysqld --some --flags` after `ENTRYPOINT` runs `initdb`).
This is nice because the image name can double as a refernce to the binary as
shown in the command above.
People also often use `ENTRYPOINT` is as a helper script.
For example, let’s look at the `Dockerfile` for the
[Postgres Official Image](https://github.com/docker-library/postgres).