dataflow/ubuntu-container: use LTS ubuntu version (GoogleCloudPlatform#8215)

Author: David Cavazos

dataflow/custom-containers/ubuntu/Dockerfile

@@ -12,21 +12,21 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM ubuntu:impish
+FROM ubuntu:focal
 
 WORKDIR /pipeline
 
 # Set the entrypoint to Apache Beam SDK worker launcher.
-COPY --from=apache/beam_python3.9_sdk:2.38.0 /opt/apache/beam /opt/apache/beam
+COPY --from=apache/beam_python3.8_sdk:2.40.0 /opt/apache/beam /opt/apache/beam
 ENTRYPOINT [ "/opt/apache/beam/boot" ]
 
 # Install Python with pip, dev tools, distutils, and a C++ compiler.
 COPY requirements.txt .
 RUN apt-get update \
     && apt-get install -y --no-install-recommends \
-        ca-certificates curl g++ python3.9-dev python3-distutils \
+        ca-certificates curl g++ python3-dev python3-distutils \
     && rm -rf /var/lib/apt/lists/* \
-    && update-alternatives --install /usr/bin/python python /usr/bin/python3.9 10 \
+    && update-alternatives --install /usr/bin/python python /usr/bin/python3 10 \
     && curl https://bootstrap.pypa.io/get-pip.py | python \
     # Install the requirements.
     && pip install --no-cache-dir -r requirements.txt \

dataflow/custom-containers/ubuntu/requirements.txt

@@ -1 +1 @@
-apache-beam[gcp]==2.37.0
+apache-beam[gcp]==2.40.0