Remove Debian 10 support.

As a consequence:

• Bump minimum supported Python version to 3.8.
• Move Vagrant environment to Ubuntu 20.04, which has Python 3.8.
• Move CI frontend tests to Ubuntu 20.04.
• Move production build test to Ubuntu 20.04.
• Move 3.4 upgrade test to Ubuntu 20.04.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

.github/workflows/production-suite.yml

@@ -30,13 +30,13 @@ jobs:
   production_build:
     # This job builds a release tarball from the current commit, which
     # will be used for all of the following install/upgrade tests.
-    name: Debian 10 production build
+    name: Ubuntu 20.04 production build
     runs-on: ubuntu-latest
 
     # Docker images are built from 'tools/ci/Dockerfile'; the comments at
     # the top explain how to build and upload these images.
-    # Debian 10 ships with Python 3.7.3.
-    container: zulip/ci:buster
+    # Ubuntu 20.04 ships with Python 3.8.10.
+    container: zulip/ci:focal
     steps:
       - name: Add required permissions
         run: |
@@ -66,22 +66,22 @@ jobs:
         uses: actions/cache@v2
         with:
           path: /srv/zulip-npm-cache
-          key: v1-yarn-deps-buster-${{ hashFiles('package.json') }}-${{ hashFiles('yarn.lock') }}
-          restore-keys: v1-yarn-deps-buster
+          key: v1-yarn-deps-focal-${{ hashFiles('package.json') }}-${{ hashFiles('yarn.lock') }}
+          restore-keys: v1-yarn-deps-focal
 
       - name: Restore python cache
         uses: actions/cache@v2
         with:
           path: /srv/zulip-venv-cache
-          key: v1-venv-buster-${{ hashFiles('requirements/dev.txt') }}
-          restore-keys: v1-venv-buster
+          key: v1-venv-focal-${{ hashFiles('requirements/dev.txt') }}
+          restore-keys: v1-venv-focal
 
       - name: Restore emoji cache
         uses: actions/cache@v2
         with:
           path: /srv/zulip-emoji-cache
-          key: v1-emoji-buster-${{ hashFiles('tools/setup/emoji/emoji_map.json') }}-${{ hashFiles('tools/setup/emoji/build_emoji') }}-${{ hashFiles('tools/setup/emoji/emoji_setup_utils.py') }}-${{ hashFiles('tools/setup/emoji/emoji_names.py') }}-${{ hashFiles('package.json') }}
-          restore-keys: v1-emoji-buster
+          key: v1-emoji-focal-${{ hashFiles('tools/setup/emoji/emoji_map.json') }}-${{ hashFiles('tools/setup/emoji/build_emoji') }}-${{ hashFiles('tools/setup/emoji/emoji_setup_utils.py') }}-${{ hashFiles('tools/setup/emoji/emoji_names.py') }}-${{ hashFiles('package.json') }}
+          restore-keys: v1-emoji-focal
 
       - name: Build production tarball
         run: ./tools/ci/production-build
@@ -114,15 +114,10 @@ jobs:
             os: focal
             extra_args: ""
 
-          - docker_image: zulip/ci:buster
-            name: Debian 10 production install with custom db name and user
-            os: buster
-            extra_args: --test-custom-db
-
           - docker_image: zulip/ci:bullseye
-            name: Debian 11 production install
+            name: Debian 11 production install with custom db name and user
             os: bullseye
-            extra_args: ""
+            extra_args: --test-custom-db
 
     name: ${{ matrix.name  }}
     container:
@@ -209,10 +204,9 @@ jobs:
         include:
           # Docker images are built from 'tools/ci/Dockerfile'; the comments at
           # the top explain how to build and upload these images.
-          - docker_image: zulip/ci:buster-3.4
+          - docker_image: zulip/ci:focal-3.4
             name: 3.4 Version Upgrade
-            os: buster
-
+            os: focal
           - docker_image: zulip/ci:bullseye-4.11
             name: 4.11 Version Upgrade
             os: bullseye

.github/workflows/zulip-ci.yml

@@ -18,19 +18,14 @@ jobs:
         include:
           # Base images are built using `tools/ci/Dockerfile.prod.template`.
           # The comments at the top explain how to build and upload these images.
-          # Debian 10 ships with Python 3.7.3.
-          - docker_image: zulip/ci:buster
-            name: Debian 10 Buster (Python 3.7, backend + frontend)
-            os: buster
-            include_frontend_tests: true
-          # Ubuntu 20.04 ships with Python 3.8.2.
+          # Ubuntu 20.04 ships with Python 3.8.10.
           - docker_image: zulip/ci:focal
-            name: Ubuntu 20.04 Focal (Python 3.8, backend)
+            name: Ubuntu 20.04 (Python 3.8, backend + frontend)
             os: focal
-            include_frontend_tests: false
+            include_frontend_tests: true
           # Debian 11 ships with Python 3.9.2.
           - docker_image: zulip/ci:bullseye
-            name: Debian 11 Bullseye (Python 3.9, backend)
+            name: Debian 11 (Python 3.9, backend)
             os: bullseye
             include_frontend_tests: false
 
@@ -124,8 +119,9 @@ jobs:
         run: |
           source tools/ci/activate-venv
 
-          # Currently our compiled requirements files will differ for different python versions
-          # so we will run test-locked-requirements only for Debian 10.
+          # Currently our compiled requirements files will differ for different
+          # Python versions, so we will run test-locked-requirements only on the
+          # platform with the oldest one.
           # ./tools/test-locked-requirements
           # ./tools/test-run-dev  # https://github.com/zulip/zulip/pull/14233
           #
@@ -192,7 +188,7 @@ jobs:
           fi
 
       - name: Test locked requirements
-        if: ${{ matrix.os == 'buster' }}
+        if: ${{ matrix.os == 'focal' }}
         run: |
           . /srv/zulip-py3-venv/bin/activate && \
           ./tools/test-locked-requirements
@@ -216,7 +212,6 @@ jobs:
           retention-days: 60
 
       - name: Check development database build
-        if: ${{ matrix.os == 'focal' || matrix.os == 'bullseye' || matrix.os == 'jammy' }}
         run: ./tools/ci/setup-backend
 
       - name: Report status