Enhance Dockerfile: Add Postgres libs and fix libpq symlink for compatibility with PG 15/16

Author: m3hm3t

circleci/images/exttester/Dockerfile

@@ -89,6 +89,9 @@ FROM buildpack-deps:bullseye
 # add unpriviliged user for tests
 RUN useradd -ms /bin/bash circleci
 
+# bring in the built Postgres libs so pg_regress_multi’s LD_LIBRARY_PATH has something to find
+COPY --from=dev-tools-builder /build /build
+
 RUN <<'EOF'
 # install dependencies
 set -eux
@@ -183,7 +186,24 @@ ENV PATH=/usr/lib/postgresql/$PG_MAJOR/bin/:$PATH
 # setup /var/run/postgresql for use with circleci
 RUN mkdir -p /var/run/postgresql && chown -R postgres:postgres /var/run/postgresql && chmod 2777 /var/run/postgresql
 
-# copy the collected files from the collection container at once into the final container
-COPY --from=dev-tools-collection /collect/ /
+# --------------------------------------------------------------------
+# The COPY above can white‑out /usr/lib/x86_64-linux-gnu when BuildKit
+# is active, removing libpq.so.* that was installed earlier.  We
+# (re)install libpq5, recreate the helper symlink for PG ≤ 16, refresh
+# the loader cache, and preload the client library so Citus  never
+# complains about symbol interposition.
+# --------------------------------------------------------------------
+ARG PG_MAJOR
+RUN set -eux; \
+    # 2.  Satisfy RUNPATH for PG 15/16 (harmless for ≥17)
+    ln -sf /usr/lib/x86_64-linux-gnu/libpq.so.5 \
+           /usr/lib/postgresql/${PG_MAJOR}/lib/libpq.so.5; \
+    \
+    # 3.  Refresh dynamic‑linker cache
+    echo "/usr/lib/x86_64-linux-gnu" > /etc/ld.so.conf.d/libpq.conf; \
+    ldconfig
+
+# 4.  Make sure the backend and Citus load the *same* libpq object
+ENV LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libpq.so.5
 
 WORKDIR /home/circleci