In skeleton, add worker code

skeleton/worker/BUILD.bazel

@@ -0,0 +1,54 @@
+load("@rules_python//python:defs.bzl", "py_binary")
+load("//tools/build_rules:cross_platform_image.bzl", "cross_platform_image")
+load("//tools/build_rules:py_layer.bzl", "py_oci_image")
+
+py_binary(
+    name = "binary",
+    srcs = ["app.py"],
+    imports = [".."],
+    main = "app.py",
+    visibility = ["//:__subpackages__"],
+    deps = ["//skeleton:config_py"],
+)
+
+py_oci_image(
+    name = "base_image",
+    base = "@python3_image",
+    binaries = [
+        "//scripts:wait_for_postgres",
+        ":binary",
+    ],
+    cmd = [
+        "/" + package_name() + "/binary",
+    ],
+    entrypoint = [
+        "/scripts/wait_for_postgres",
+    ],
+    env = {
+        "FLASK_APP": "app.py",
+        "FLASK_DEBUG": "True",
+        "API_PORT": "5000",
+        "FRONTEND_PROTOCOL": "http",
+        "FRONTEND_HOST": "frontend",
+        "FRONTEND_PORT": "5001",
+        "DB_HOST": "pg",
+        "DB_USERNAME": "admin",
+        "DB_PASSWORD": "development",
+        "DATABASE_NAME": "api_development",
+        "FITBIT_CLIENT_ID": "testing",
+        "FITBIT_CLIENT_SECRET": "testing",
+        "FITBIT_VERIFICATION_CODE": "testing",
+        "FLASK_SECRET_KEY": "testing",
+    },
+    tags = ["manual"],
+)
+
+# $ bazel run //skeleton/worker:image_tarball
+# $ docker run --rm shaldengeki/skeleton-worker:latest
+cross_platform_image(
+    name = "image",
+    image = ":base_image",
+    repo_tags = ["shaldengeki/skeleton-worker:latest"],
+    repository = "docker.io/shaldengeki/skeleton-worker",
+    visibility = ["//skeleton/worker:__subpackages__"],
+)

skeleton/worker/app.py

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+import time
+
+from fitbit_challenges.config import app, db
+
+max_delay = 10
+
+
+def main() -> int:
+    with app.app_context():
+        while True:
+            start = time.time()
+            # Do work here.
+            delay = (start + max_delay) - time.time()
+            if delay > 0:
+                time.sleep(delay)
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())