Add plpython3 Extension to Postgres/timescaledb Alpine Docker Image - postgresql

Question

I try to add the plpython3 extension to my timescaledb/postgres (based on linux alpine) image:
FROM timescale/timescaledb:0.9.0-pg10
RUN set -ex \
&& apk add --no-cache --virtual .plpython3-deps --repository http://nl.alpinelinux.org/alpine/edge/testing \
postgresql-plpython3
When I try to create the extension I get the following error:
postgres=# CREATE EXTENSION plpython3u;
ERROR: could not open extension control file "/usr/local/share/postgresql/extension/plpython3u.control": No such file or directory
But when I search for the files inside my container I can find them within a different directory:
/ # find / -name '*plpy*'
/usr/lib/postgresql/plpython3.so
/usr/share/postgresql/extension/plpython3u.control
/usr/share/postgresql/extension/plpython3u--1.0.sql
/usr/share/postgresql/extension/plpython3u--unpackaged--1.0.sql
How can I install postgresql-plpython3 to a different directory or configure postgres to recognize my added extension?
Update
When I just mv the files to /usr/local/share/postgresql/extension I get the error:
postgres=# CREATE EXTENSION plpython3u;
ERROR: could not access file "$libdir/plpython3": No such file or directory
Update 2
So the issue with $libdir was that pg_config --pkglibdir points to /usr/local/lib/postgresql but plpython3.so is inside /usr/lib/postgresql. When I move everything to the according /usr/local directories I can successfully create the extension.
This leads to the question where I hope to find an answer. How can I install postgresql-plpython3 to /usr/local/... instead of /usr/...?

Answer 1

I am fairly certain that if you use prebuilt packages you are stuck with hardcoded installation paths.
The easiest way around your problem is to create symlinks after installation:
FROM timescale/timescaledb:0.9.0-pg10
RUN set -ex \
&& apk add --no-cache --virtual .plpython3-deps --repository http://nl.alpinelinux.org/alpine/edge/testing \
postgresql-plpython3 \
&& ln -s /usr/lib/postgresql/plpython3.so /usr/local/lib/postgresql/plpython3.so \
&& ln -s /usr/share/postgresql/extension/plpython3u.control /usr/local/share/postgresql/extension/plpython3u.control \
&& ln -s /usr/share/postgresql/extension/plpython3u--1.0.sql /usr/local/share/postgresql/extension/plpython3u--1.0.sql \
&& ln -s /usr/share/postgresql/extension/plpython3u--unpackaged--1.0.sql /usr/local/share/postgresql/extension/plpython3u--unpackaged--1.0.sql