The base ubuntu:20.04 image does not have the necessary CA certificates to verify the SSL certificate of the internal mirror mirror.bazel.build via HTTPS. Even though the sed

  command replaced http://archive.ubuntu.com with http://mirror.bazel.build, the apt configuration or the mirror itself was likely redirecting to HTTPS, which then failed.
I have updated buildscripts/grpc-java-artifacts/Dockerfile.multiarch.base to ensure it uses HTTP for the mirror.

Author: kannanjgithub

buildscripts/grpc-java-artifacts/Dockerfile.multiarch.base

@@ -1,4 +1,8 @@
-FROM ubuntu:18.04
+FROM ubuntu:20.04
+
+# Redirect to the internal mirror to bypass the Kokoro network block
+# We use http instead of https because the base image lacks certificates to verify mirror.bazel.build
+RUN sed -i 's|http://archive.ubuntu.com/ubuntu/|http://mirror.bazel.build/archive.ubuntu.com/ubuntu/|g' /etc/apt/sources.list
 
 RUN export DEBIAN_FRONTEND=noninteractive && \
     apt-get update && \
@@ -9,12 +13,12 @@ RUN export DEBIAN_FRONTEND=noninteractive && \
         curl \
         g++-aarch64-linux-gnu \
         g++-powerpc64le-linux-gnu \
-        openjdk-8-jdk \
+        g++-s390x-linux-gnu \
+        openjdk-11-jdk \
         pkg-config \
         && \
     rm -rf /var/lib/apt/lists/*
 
 RUN curl -Ls https://github.com/Kitware/CMake/releases/download/v3.26.3/cmake-3.26.3-linux-x86_64.tar.gz | \
     tar xz -C /var/local
 ENV PATH /var/local/cmake-3.26.3-linux-x86_64/bin:$PATH
-