docker-ssh-exec - Secure SSH key injection for Docker builds
Allows commands that require an SSH key to be run from within a
Dockerfile, without leaving the key in the resulting image.
This program runs in two different modes:
- a server mode, run as the Docker image
mdsol/docker-ssh-exec, which transmits an SSH key on request to the the client; and
- a client mode, invoked from within the
Dockerfile, that grabs the key from the server, writes it to the filesystem, runs the desired build command, and then deletes the key before the filesystem is snapshotted into the build.
To install the server, just pull
mdsol/docker-ssh-exec like any other Docker image.
To install the client, just grab it from the releases page, uncompress the archive, and copy the binary to somewhere in your
$PATH. Remember that the client is run during the
docker build... process, so either install the client just before invoking it, or make sure it's already present in your source image. Here's an example of the code you might run in your source image, to prepare it for SSH cloning from GitHub:
# install Medidata docker-ssh-exec build tool from S3 bucket "mybucket" curl https://s3.amazonaws.com/mybucket/docker-ssh-exec/\ docker-ssh-exec_0.5.1_linux_amd64.tar.gz | \ tar -xz --strip-components=1 -C /usr/local/bin \ docker-ssh-exec_0.5.1_linux_amd64/docker-ssh-exec mkdir -p /root/.ssh && chmod 0700 /root/.ssh ssh-keyscan github.com >/root/.ssh/known_hosts
To run the server component, pass it the private half of your SSH key, either as a shared volume:
docker run -v ~/.ssh/id_rsa:/root/.ssh/id_rsa --name=keyserver -d \ mdsol/docker-ssh-exec -server
or as an ENV var:
docker run -e DOCKER-SSH-KEY="$(cat ~/.ssh/id_rsa)" --name=keyserver -d \ mdsol/docker-ssh-exec -server
The benefit of this second method is that OS X systems using a virtual Docker host cannot easily use Docker's shared volume feature with files on the OS X side. The drawback is that the kay data is exposed in the process list.
Then, run a quick test of the client, to make sure it can get the key:
docker run --rm -it mdsol/docker-ssh-exec cat /root/.ssh/id_rsa
Finally, as long as the source image is set up to trust (or ignore) GitHub's server key, you can clone private repositories from within the
Dockerfile like this:
docker-exec-ssh git clone email@example.com:my_user/my_private_repo.git
The client first transfers the key from the server, writing it to
$HOME/.ssh/id_rsa (by default), then executes whatever command you supply as arguments. Before exiting, it deletes the key from the filesystem.
Here's the command-line help:
Usage of docker-ssh-exec: -key string path to key file (default "~/.ssh/id_rsa") -port int server receiving port (default 1067) -pwd string password for encrypted RSA key -server run key server instead of command -version print version and exit -wait int client timeout, in seconds (default 3)
The software quits with a non-zero exit code (>100) on any error -- except a timeout from the keyserver, in which case it will just ignore the timeout and try to run the build command anyway. If the build command fails,
docker-ssh-exec returns the exit code of the failed command.
Known Limitations / Bugs
The key data is limited to 4096 bytes.
Contribution / Development
This software was created by Benton Roberts (firstname.lastname@example.org)
To build it yourself, just
go get and
go install as usual:
go get github.com/mdsol/docker-ssh-exec cd $GOPATH/src/github.com/mdsol/docker-ssh-exec go install