Unlike `docker build --secret`, `docker build --ssh` allows the build container to
use SSH keys with passphrases.
$ eval $(ssh-agent)
$ ssh-add ~/.ssh/id_rsa
(Input your passphrase here)
$ docker build --ssh default=$SSH_AUTH_SOCK ...
This feature requires the daemon with `CapExecMountSSH` build capability (moby/moby#37973) .
Currently, the official Dockerfile frontend does not provide the syntax for using the SSH forwarder.
However, the experimental `RUN --mount=type=ssh` syntax can be enabled by using
the Dockerfile frontend image built with the `BUILDTAGS="dfrunmount dfssh"`, via the `# syntax =` "shebang".
The Dockerfile for the Dockerfile frontend is available at github.com/moby/buildkit/frontend/dockerfile/cmd/dockerfile-frontend)
The pre-built image is also available as `tonistiigi/dockerfile:ssh20181002` .
An example Dockerfile with `RUN --mount=type=ssh`:
# syntax = tonistiigi/dockerfile:ssh20181002
FROM alpine
RUN apk add --no-cache openssh-client
RUN mkdir -p -m 0700 ~/.ssh && ssh-keyscan gitlab.com >> ~/.ssh/known_hosts
RUN --mount=type=ssh ssh git@gitlab.com | tee /hello
# "Welcome to GitLab, @GITLAB_USERNAME_ASSOCIATED_WITH_SSHKEY" should be printed here
More info available at moby/buildkit#608, moby/buildkit#655
Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
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