prepare build job

.azure-pipelines/advanced-test.yml

@@ -5,5 +5,10 @@ trigger:
   - test-*
 pr: none
 
+variables:
+  # We don't publish our Docker images in this pipeline, but when building them
+  # for testing, let's use the nightly tag.
+  dockerTag: nightly
+
 stages:
   - template: templates/stages/test-and-package-stage.yml

.azure-pipelines/nightly.yml

@@ -9,6 +9,9 @@ schedules:
       - master
     always: true
 
+variables:
+  dockerTag: nightly
+
 stages:
   - template: templates/stages/test-and-package-stage.yml
   - template: templates/stages/deploy-stage.yml

.azure-pipelines/release.yml

@@ -6,11 +6,13 @@ trigger:
       - v*
 pr: none
 
+variables:
+  dockerTag: ${{variables['Build.SourceBranchName']}}
+
 stages:
   - template: templates/stages/test-and-package-stage.yml
   - template: templates/stages/changelog-stage.yml
   - template: templates/stages/deploy-stage.yml
     parameters:
       snapReleaseChannel: beta
-      dockerTag: ${{variables['Build.SourceBranchName']}}
   - template: templates/stages/notify-failure-stage.yml

.azure-pipelines/templates/jobs/packaging-jobs.yml

@@ -3,10 +3,21 @@ jobs:
     pool:
       vmImage: ubuntu-18.04
     steps:
-      - bash: |
-          tools/docker/build.sh $(dockerTag)
-          docker images --filter reference='*/dns-*' --filter reference='*/certbot'
+      - bash: tools/docker/build.sh ${{ variables.dockerTag }}
         displayName: Build the Docker images
+      # We don't filter for the Docker Hub organization to continue to allow
+      # easy testing of these scripts on forks.
+      - bash: |
+          DOCKER_IMAGES=$(docker images --quiet --filter reference='*/dns-*' --filter reference='*/certbot')
+          docker save --output docker_images.tar $DOCKER_IMAGES
+        displayName: Save the Docker images
+      - bash: mv docker_images.tar $(Build.ArtifactStagingDirectory)
+        displayName: Prepare Docker artifact
+      - task: PublishPipelineArtifact@1
+        inputs:
+          path: $(Build.ArtifactStagingDirectory)
+          artifact: docker_images
+        displayName: Store Docker artifact
   - job: installer_build
     pool:
       vmImage: vs2017-win2016