diff --git a/action.Dockerfile b/action.Dockerfile
index ddf84cf..da65b9b 100644
--- a/action.Dockerfile
+++ b/action.Dockerfile
@@ -1,5 +1,5 @@
 FROM icinga/icingaweb2-builder
 
-COPY action.bash Dockerfile get-mods.sh icingaweb2.patch /
+COPY action.bash composer.bash Dockerfile get-mods.sh icingaweb2.patch /
 
 CMD ["/action.bash"]
diff --git a/action.bash b/action.bash
index 631f286..0c87879 100755
--- a/action.bash
+++ b/action.bash
@@ -9,18 +9,9 @@ mkimg () {
 	node /actions/checkout/dist/index.js |grep -vFe ::add-matcher::
 
 	git archive --prefix=icingaweb2/ HEAD |tar -x
+
 	/get-mods.sh "$1"
-
-	for d in icingaweb2 icingaweb2/modules/*; do
-		pushd "$d"
-
-		if [ -e composer.json ]; then
-			composer install --no-dev --ignore-platform-reqs
-		fi
-
-		popd
-	done
-
+	/composer.bash
 	patch -d icingaweb2 -p0 < /icingaweb2.patch
 
 	docker build -f /Dockerfile -t "${TARGET}:$TAG" .
diff --git a/build.bash b/build.bash
new file mode 100755
index 0000000..15bd021
--- /dev/null
+++ b/build.bash
@@ -0,0 +1,37 @@
+#!/bin/bash
+set -exo pipefail
+
+IW2SRC="$1"
+export MODS_BRANCH="$2"
+
+if [ -z "$IW2SRC" ]; then
+	cat <<EOF >&2
+Usage: ${0} /icingaweb2/source/dir
+EOF
+
+	false
+fi
+
+IW2SRC="$(realpath "$IW2SRC")"
+BLDCTX="$(realpath "$(dirname "$0")")"
+
+docker build -f "${BLDCTX}/action-base.Dockerfile" -t icinga/icingaweb2-builder "$BLDCTX"
+docker build -f "${BLDCTX}/deps.Dockerfile" -t icinga/icingaweb2-deps "$BLDCTX"
+
+docker run --rm -i \
+	-v "${IW2SRC}:/iw2src:ro" \
+	-v "${BLDCTX}:/bldctx:ro" \
+	-v /var/run/docker.sock:/var/run/docker.sock \
+	-e MODS_BRANCH \
+	icinga/icingaweb2-builder bash <<EOF
+set -exo pipefail
+
+git -C /iw2src archive --prefix=iw2cp/icingaweb2/ HEAD |tar -xC /
+cd /iw2cp
+
+/bldctx/get-mods.sh "$MODS_BRANCH"
+/bldctx/composer.bash
+patch -d icingaweb2 -p0 < /bldctx/icingaweb2.patch
+
+docker build -f /bldctx/Dockerfile -t icinga/icingaweb2 .
+EOF
diff --git a/composer.bash b/composer.bash
new file mode 100755
index 0000000..06382b6
--- /dev/null
+++ b/composer.bash
@@ -0,0 +1,12 @@
+#!/bin/bash
+set -exo pipefail
+
+for d in icingaweb2 icingaweb2/modules/*; do
+	pushd "$d"
+
+	if [ -e composer.json ]; then
+		composer install --no-dev --ignore-platform-reqs
+	fi
+
+	popd
+done