[dockerhub] push arm64 images too, with multiarch tags

BUILD.bazel

@@ -71,6 +71,7 @@ container_image(
     name = "bazel-remote-image",
     base = ":bazel-remote-base",
     cmd = ["--max_size=5"],
+    architecture = "amd64",
     entrypoint = [
         "/app/bazel-remote-base.binary",
         "--port=8080",
@@ -93,6 +94,7 @@ container_image(
 container_image(
     name = "bazel-remote-image-arm64",
     base = ":bazel-remote-base-arm64",
+    architecture = "arm64",
     cmd = ["--max_size=1"],
     entrypoint = [
         "/app/bazel-remote-base-arm64.binary",
@@ -113,12 +115,31 @@ container_image(
     visibility = ["//visibility:public"],
 )
 
+# The following container_push targets push to "tmp-amd64" and "tmp-arm64"
+# tags, so they can be combined into a multiarch tag on dockerhub. This
+# isn't currently possible with rules_docker, so instead we rely on some
+# external commands to be run after the tmp-* tags are pushed. See the
+# docker/push_to_dockerhub script.
+#
+# Background:
+# https://github.com/bazelbuild/rules_docker/issues/1599
+
 container_push(
-    name = "push_to_dockerhub",
+    name = "push_to_dockerhub_amd64",
     format = "Docker",
     image = ":bazel-remote-image",
     registry = "index.docker.io",
     repository = "buchgr/bazel-remote-cache",
-    tag = "latest",
+    tag = "tmp-amd64",
+    visibility = ["//visibility:public"],
+)
+
+container_push(
+    name = "push_to_dockerhub_arm64",
+    format = "Docker",
+    image = ":bazel-remote-image-arm64",
+    registry = "index.docker.io",
+    repository = "buchgr/bazel-remote-cache",
+    tag = "tmp-arm64",
     visibility = ["//visibility:public"],
 )

docker/push_to_dockerhub

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+script_dir=$(dirname "${BASH_SOURCE[0]}")
+cd "${script_dir}/.."
+
+# push test-amd64 and test-arm64 images.
+bazel run //:push_to_dockerhub_amd64
+bazel run //:push_to_dockerhub_arm64
+
+# Create the multiarch manifest.
+docker manifest rm buchgr/bazel-remote-cache:latest
+docker manifest create buchgr/bazel-remote-cache:latest \
+    --amend buchgr/bazel-remote-cache:tmp-amd64 \
+    --amend buchgr/bazel-remote-cache:tmp-arm64
+
+# Push the multiarch manifest
+docker manifest push buchgr/bazel-remote-cache:latest
+
+echo "Go ahead and delete the tmp-amd64 and tmp-arm64 images from the web ui"