using ssh key in docker image

Dockerfile

# add credentials on build
ARG SSH_PRIVATE_KEY
RUN mkdir /root/.ssh/
RUN echo "${SSH_PRIVATE_KEY}" > /root/.ssh/id_rsa
RUN chmod 600 /root/.ssh/id_rsa

# make sure your domain is accepted
RUN touch /root/.ssh/known_hosts
RUN ssh-keyscan bitbucket.org >> /root/.ssh/known_hosts

# use as below when building docker image
# docker build -t . --build-arg SSH_PRIVATE_KEY="$(cat <path-to-private-key>)"
# WARNING: not to expose your private key in docker image, use multi stage build and add your key 
# WARNING: as `cat` is used this will make private-key visible if stdout is logged or displayed