Hack to launch jupyter-server (#113)

* omit .git dir from image

* dockerfile cleanup: reduce size of repo with `COPY --chown`

COPY/RUN chown doubles the size of the repo in the image

also make sure NB_USER is not empty and present in system info

* hack: launch jupyter-server instead of jupyter-notebook

BinderHub forces a launch of the legacy jupyter-notebook server,
but our base image has upgraded jupyterlab and jupyter-server to a version that doesn't support it

the alternative would be to pin-down jupyter server and everything using it

.dockerignore

@@ -0,0 +1,2 @@
+# Don't include the .git in the image. It's big!
+.git

Dockerfile

@@ -1,16 +1,21 @@
 FROM ghcr.io/jorgensd/dolfinx-tutorial:v0.6.0
 
 # create user with a home directory
-ARG NB_USER
+ARG NB_USER=jovyan
 ARG NB_UID=1000
-ENV USER ${NB_USER}
+RUN useradd -m ${NB_USER} -u ${NB_UID}
 ENV HOME /home/${NB_USER}
 
+# for binder: base image upgrades lab to require jupyter-server 2,
+# but binder explicitly launches jupyter-notebook
+# force binder to launch jupyter-server instead
+RUN nb=$(which jupyter-notebook) \
+ && rm $nb \
+ && ln -s $(which jupyter-lab) $nb
+
 # Copy home directory for usage in binder
 WORKDIR ${HOME}
-COPY . ${HOME}
-USER root
-RUN chown -R ${NB_UID} ${HOME}
+COPY --chown=${NB_UID} . ${HOME}
 
 USER ${NB_USER}
-ENTRYPOINT []
+ENTRYPOINT []