Use bundled JDK in Docker images (#40238)

Now that we have the bundled JDK in the Docker images, we should use
them as opposed to procuring a JDK ourselves. This commit replaces the
JDK in the Docker image with the bundled JDK.

distribution/docker/build.gradle

@@ -22,8 +22,6 @@ ext.expansions = { oss ->
   final String elasticsearch = oss ? "elasticsearch-oss-${VersionProperties.elasticsearch}-${classifier}.tar.gz" : "elasticsearch-${VersionProperties.elasticsearch}-${classifier}.tar.gz"
   return [
     'elasticsearch'       : elasticsearch,
-    'jdkUrl'              : 'https://download.java.net/java/GA/jdk12/GPL/openjdk-12_linux-x64_bin.tar.gz',
-    'jdkVersion'          : '12',
     'license'             : oss ? 'Apache-2.0' : 'Elastic License',
     'source_elasticsearch': local() ? "COPY $elasticsearch /opt/" : "RUN curl --retry 8 -s -L -O https://artifacts.elastic.co/downloads/elasticsearch/${elasticsearch}",
     'version'             : VersionProperties.elasticsearch

distribution/docker/src/docker/Dockerfile

@@ -14,14 +14,6 @@
 FROM centos:7 AS builder
 
 ENV PATH /usr/share/elasticsearch/bin:$PATH
-ENV JAVA_HOME /opt/jdk-${jdkVersion}
-
-RUN curl --retry 8 -s ${jdkUrl} | tar -C /opt -zxf -
-
-# Replace OpenJDK's built-in CA certificate keystore with the one from the OS
-# vendor. The latter is superior in several ways.
-# REF: https://github.com/elastic/elasticsearch-docker/issues/171
-RUN ln -sf /etc/pki/ca-trust/extracted/java/cacerts /opt/jdk-${jdkVersion}/lib/security/cacerts
 
 RUN groupadd -g 1000 elasticsearch && \
     adduser -u 1000 -g 1000 -d /usr/share/elasticsearch elasticsearch
@@ -46,9 +38,6 @@ COPY config/elasticsearch.yml config/log4j2.properties config/
 FROM centos:7
 
 ENV ELASTIC_CONTAINER true
-ENV JAVA_HOME /opt/jdk-${jdkVersion}
-
-COPY --from=builder /opt/jdk-${jdkVersion} /opt/jdk-${jdkVersion}
 
 RUN yum update -y && \
     yum install -y nc && \
@@ -61,6 +50,12 @@ RUN groupadd -g 1000 elasticsearch && \
 
 WORKDIR /usr/share/elasticsearch
 COPY --from=builder --chown=1000:0 /usr/share/elasticsearch /usr/share/elasticsearch
+
+# Replace OpenJDK's built-in CA certificate keystore with the one from the OS
+# vendor. The latter is superior in several ways.
+# REF: https://github.com/elastic/elasticsearch-docker/issues/171
+RUN ln -sf /etc/pki/ca-trust/extracted/java/cacerts /usr/share/elasticsearch/jdk/lib/security/cacerts
+
 ENV PATH /usr/share/elasticsearch/bin:$PATH
 
 COPY --chown=1000:0 bin/docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh