Running SQLite in a Zero2Kubernetes (Azure) JupyterHub Spawned Jupyter Notebook Server

I think this is an issue, or it may just be a quirk of a container I built for deployment via JupyterHub using Kubernetes on Azure to run user containers, but it seems you that SQLite does things with file locks that break can the sqlite3 package…

For example, the hacky cross-notebook search engine I built, the PyPi installable nbsearch, (which is not the same as the IBM semantic notebook search of the same name, WatViz/nbsearch) indexes notebooks into a SQLite database saved into a hidden directory in home.

The nbsearch UI is published using Jupyter server proxy. When the Jupyter noteobook server starts, the jupyter-server-proxy extension looks for packages with jupyter-server-proxy registered start hooks (code).

If the jupyter-server-proxy setup fails for for one registered service, it seems to fail for them all. During testing of a deployment, I noticed none of the jupyter-server-proxy services I expected to be visible from the notebook homepage New menu were there.

Checking logs (via @yuvipanda, kubectl logs -n <namespace> jupyter-<username>) it seemed that an initialisation script in nbsearch was failing the whole jupyter-server-proxy setup (sqlite3.OperationalError: database is locked; related issue).

Scanning the JupyterHub docs, I noted that:

> The SQLite database should not be used on NFS. SQLite uses reader/writer locks to control access to the database. This locking mechanism might not work correctly if the database file is kept on an NFS filesystem. This is because fcntl() file locking is broken on many NFS implementations. Therefore, you should avoid putting SQLite database files on NFS since it will not handle well multiple processes which might try to access the file at the same time.

This relates to setting up the JupyterHub service, but it did put me on the track of various other issues perhaps related to my issue posted variously around the web. For example, this issueAllow nobrl parameter like docker to use sqlite over network drive — suggests alternative file mountOptions which seemed to fix things…

Author: Tony Hirst

I'm a Senior Lecturer at The Open University, with an interest in #opendata policy and practice, as well as general web tinkering...

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