Support different container registry to push and pull

[rgaiacs]

This covers #1903.

[rgaiacs]

When I run locally and request a launch for https://github.com/binder-examples/requirements, the output was

Waiting for build to start...
Picked Git content provider.
Cloning into '/tmp/repo2dockersul_16w8'...
HEAD is now at 50533eb Merge pull request #21 from minrk/default-branch
Building conda environment for python=3.10
Using PythonBuildPack builder
Step 1/50 : FROM docker.io/library/buildpack-deps:jammy
 ---> 9c6387be7092
...
Step 50/50 : CMD ["jupyter", "notebook", "--ip", "0.0.0.0"]
 ---> Running in ee6ff4f7fcc2
 ---> Removed intermediate container ee6ff4f7fcc2
 ---> 6a38d51aece6
{"aux": {"ID": "sha256:6a38d51aece6f13a0a23116b2b4050ddd094a00a87eea438317bc298af4d5800"}}Successfully built 6a38d51aece6
Successfully tagged gesiscss/binder-binder-2dexamples-2drequirements-55ab5c:50533eb470ee6c24e872043d30b2fee463d6943f
Exception ignored in: <function Application.__del__ at 0x7fad6b188900>
Traceback (most recent call last):
  File "/opt/venv/lib/python3.11/site-packages/traitlets/config/application.py", line 1065, in __del__
  File "/opt/venv/lib/python3.11/site-packages/traitlets/config/application.py", line 1054, in close_handlers
  File "/opt/venv/lib/python3.11/site-packages/traitlets/traitlets.py", line 687, in __get__
  File "/opt/venv/lib/python3.11/site-packages/traitlets/traitlets.py", line 666, in get
TypeError: 'NoneType' object is not callable
Built image, launching...
Launching server...
Launch attempt 1 failed, retrying...
Launch attempt 2 failed, retrying...
Launch attempt 3 failed, retrying...
Failed to create temporary user for gesiscss/binder-binder-2dexamples-2drequirements-55ab5c:50533eb470ee6c24e872043d30b2fee463d6943f

There are a minor error related with traitlets. We should catch it during code review.

The launch attempt fail because I was not running Jupyter Hub locally.

[manics]

My initial thoughts are that most BinderHubs will use the same prefix for push and pull, so how about just have image_prefix as the default property as at present, and maybe add just one new property, image_prefix_pull?

I think it's fine to keep using the *_push and *_pull variables in builder.py if you want though, for clarity.

[manics]

Suggested change

	Prefix for built docker images push to container registry.
	Prefix for built docker images being pushed to the container registry.

[manics]

Suggested change

	Prefix for built docker images pull from container registry.
	Prefix for built docker images being pulled from container registry.

[rgaiacs]

My initial thoughts are that most BinderHubs will use the same prefix for push and pull

You are absolutely right. I think that 99% of BinderHubs will use a single registry. But there will be the 1% like GESIS that want to push to Docker Hub or GitHub Packages Registry and pull from a local Harbor that operates as proxy cache.

so how about just have image_prefix as the default property as at present, and maybe add just one new property, image_prefix_pull?

image_prefix is use as the default property, see https://github.com/rgaiacs/binderhub/blob/c322eabfdd78574e6b2ea03863f04ad4593060d7/binderhub/app.py#L460-L462 and https://github.com/rgaiacs/binderhub/blob/c322eabfdd78574e6b2ea03863f04ad4593060d7/binderhub/app.py#L478-L480. No change required to existing deployments.