BUILDKIT_SANDBOX_HOSTNAME build-arg

[crazy-max]

Fixes #474

FROM alpine
RUN echo "HOSTNAME envvar: $HOSTNAME" && \
  echo "hostname: $(hostname)" && \
  echo "kernel: $(cat /proc/sys/kernel/hostname)"  && \
  echo "/etc/hosts: $(cat /etc/hosts)"

$ docker buildx build --build-arg "BUILDKIT_SANDBOX_HOSTNAME=myhostname" .
...
#6 [2/2] RUN echo "HOSTNAME envvar: $HOSTNAME" &&   echo "hostname: $(hostname)" &&   echo "kernel: $(cat /proc/sys/kernel/hostname)"  &&   echo "/etc/hosts: $(cat /etc/hosts)"
#6 0.166 HOSTNAME envvar: myhostname
#6 0.166 hostname: myhostname
#6 0.167 kernel: myhostname
#6 0.168 /etc/hosts: 127.0.0.1  localhost myhostname
#6 0.168 ::1    localhost ip6-localhost ip6-loopback
#6 DONE 0.2s

@tonistiigi Do we need to add this into the Dockerfile frontend as well? ("build-arg:BUILDKIT_SANDBOX_HOSTNAME")

Signed-off-by: CrazyMax [email protected]

[tonistiigi]

Do we need to add this into the Dockerfile frontend as well?

I think it should just be in frontend