diff --git a/decision-task.py b/decision-task.py
index 9ba891ae6ec..d910808b684 100644
--- a/decision-task.py
+++ b/decision-task.py
@@ -5,9 +5,81 @@ import sys
 import json
 import taskcluster
 
-decision_task_id = os.environ["TASK_ID"]
+
+def main():
+    build_task = create_task_with_built_image(
+        "build task",
+        "./build-task.sh",
+        image="servo-x86_64-linux",
+
+        artifacts=[
+            ("executable.gz", "/repo/something-rust/something-rust.gz"),
+        ],
+
+        # https://docs.taskcluster.net/docs/reference/workers/docker-worker/docs/caches
+        scopes=[
+            "docker-worker:cache:cargo-registry-cache",
+            "docker-worker:cache:cargo-git-cache",
+        ],
+        cache={
+            "cargo-registry-cache": "/root/.cargo/registry",
+            "cargo-git-cache": "/root/.cargo/git",
+        },
+    )
+
+    create_task(
+        "run task",
+        "./run-task.sh",
+        image="buildpack-deps:bionic-scm",
+        dependencies=[build_task],
+        env={"BUILD_TASK_ID": build_task},
+    )
+
+
+# https://hub.docker.com/r/servobrowser/image-builder/
+# https://github.com/SimonSapin/servo-docker-image-builder-image
+IMAGE_BUILDER_IMAGE = "servobrowser/image-builder@sha256:" \
+    "f2370c4b28aa537e47c0cacb82cc53272233fa256b6634c0eebc46e2dd019333"
+
+# https://docs.taskcluster.net/docs/reference/workers/docker-worker/docs/environment
+DECISION_TASK_ID = os.environ["TASK_ID"]
+
 # https://docs.taskcluster.net/docs/reference/workers/docker-worker/docs/features#feature-taskclusterproxy
-queue = taskcluster.Queue(options={"baseUrl": "http://taskcluster/queue/v1/"})
+QUEUE = taskcluster.Queue(options={"baseUrl": "http://taskcluster/queue/v1/"})
+
+IMAGE_ARTIFACT_FILENAME = "image.tar.lz4"
+
+
+def create_task_with_built_image(name, command, image, **kwargs):
+    image_build_task = build_image(image)
+    kwargs.setdefault("dependencies", []).append(image_build_task)
+    image = {
+        "type": "task-image",
+        "taskId": image_build_task,
+        "path": "public/" + IMAGE_ARTIFACT_FILENAME,
+    }
+    return create_task(name, command, image, **kwargs)
+
+
+def build_image(name):
+    image_build_task = create_task(
+        "docker image build task for image: " + name,
+        """
+            docker build -t "$IMAGE" "docker/$IMAGE"
+            docker save "$IMAGE" | lz4 > /%s
+        """ % IMAGE_ARTIFACT_FILENAME,
+        env={
+            "IMAGE": name,
+        },
+        artifacts=[
+            (IMAGE_ARTIFACT_FILENAME, "/" + IMAGE_ARTIFACT_FILENAME),
+        ],
+        image=IMAGE_BUILDER_IMAGE,
+        features={
+            "dind": True,  # docker-in-docker
+        },
+    )
+    return image_build_task
 
 
 def create_task(name, command, image, artifacts=None, dependencies=None, env=None, cache=None,
@@ -18,8 +90,8 @@ def create_task(name, command, image, artifacts=None, dependencies=None, env=Non
 
     task_id = taskcluster.slugId().decode("utf8")
     payload = {
-        "taskGroupId": decision_task_id,
-        "dependencies": [decision_task_id] + (dependencies or []),
+        "taskGroupId": DECISION_TASK_ID,
+        "dependencies": [DECISION_TASK_ID] + (dependencies or []),
         "schedulerId": "taskcluster-github",
         "provisionerId": "aws-provisioner-v1",
         "workerType": "servo-docker-worker",
@@ -61,61 +133,10 @@ def create_task(name, command, image, artifacts=None, dependencies=None, env=Non
             "features": features or {},
         },
     }
-    queue.createTask(task_id, payload)
+    QUEUE.createTask(task_id, payload)
     print("Scheduled %s: %s" % (name, task_id))
     return task_id
 
-image_build_task = create_task(
-    "docker image build task",
-    """
-        docker build -t "$IMAGE" "docker/$IMAGE"
-        docker save "$IMAGE" | lz4 > /image.tar.lz4
-    """,
-    env={
-        "IMAGE": "servo-x86_64-linux",
-    },
-    artifacts=[
-        ("image.tar.lz4", "/image.tar.lz4"),
-    ],
 
-    # https://hub.docker.com/r/servobrowser/image-builder/
-    # https://github.com/SimonSapin/servo-docker-image-builder-image
-    image="servobrowser/image-builder@sha256:f2370c4b28aa537e47c0cacb82cc53272233fa256b6634c0eebc46e2dd019333",
-
-    features={
-        "dind": True,  # docker-in-docker
-    },
-)
-
-build_task = create_task(
-    "build task",
-    "./build-task.sh",
-    dependencies=[image_build_task],
-    image={
-        "type": "task-image",
-        "taskId": image_build_task,
-        "path": "public/image.tar.lz4",
-    },
-
-    artifacts=[
-        ("executable.gz", "/repo/something-rust/something-rust.gz"),
-    ],
-
-    # https://docs.taskcluster.net/docs/reference/workers/docker-worker/docs/caches
-    scopes=[
-        "docker-worker:cache:cargo-registry-cache",
-        "docker-worker:cache:cargo-git-cache",
-    ],
-    cache={
-        "cargo-registry-cache": "/root/.cargo/registry",
-        "cargo-git-cache": "/root/.cargo/git",
-    },
-)
-
-create_task(
-    "run task",
-    "./run-task.sh",
-    image="ubuntu:bionic-20180821@sha256:b5309340de7a9a540cf6c0cba3eabdfb9c9bc5153026d37991fd0028180fc725",
-    dependencies=[build_task],
-    env={"BUILD_TASK_ID": build_task},
-)
+if __name__ == "__main__":
+    main()