Add week 7 materials

materials/07-naming-lookup/seminar/consul/app.py

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+"""A small real HTTP service which registers its reachable address in Consul."""
+import json
+import os
+import socket
+import threading
+import time
+from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
+from urllib.request import Request, urlopen
+
+INSTANCE = os.environ["INSTANCE_ID"]
+CONSUL = os.environ.get("CONSUL_URL", "http://consul:8500")
+ADDRESS = socket.gethostbyname(socket.gethostname())
+
+
+class Handler(BaseHTTPRequestHandler):
+    def do_GET(self):
+        if self.path not in ("/", "/health"):
+            self.send_error(404)
+            return
+        body = json.dumps({"instance": INSTANCE, "address": ADDRESS, "port": 8080}).encode()
+        self.send_response(200)
+        self.send_header("Content-Type", "application/json")
+        self.send_header("Content-Length", str(len(body)))
+        self.end_headers()
+        self.wfile.write(body)
+
+    def log_message(self, *_):
+        pass
+
+
+def register():
+    payload = {
+        "ID": INSTANCE, "Name": "orders", "Address": ADDRESS, "Port": 8080,
+        "Check": {"HTTP": f"http://{ADDRESS}:8080/health", "Interval": "2s", "Timeout": "1s"},
+    }
+    # No automatic deregistration: the failed service stays in the catalog for comparison.
+    for attempt in range(30):
+        try:
+            request = Request(CONSUL + "/v1/agent/service/register",
+                              data=json.dumps(payload).encode(), method="PUT",
+                              headers={"Content-Type": "application/json"})
+            with urlopen(request, timeout=2) as response:
+                response.read()
+            print(f"REGISTERED orders / {INSTANCE} -> {ADDRESS}:8080", flush=True)
+            return
+        except OSError:
+            time.sleep(1)
+    raise RuntimeError("Consul registration failed after 30 attempts")
+
+
+if __name__ == "__main__":
+    server = ThreadingHTTPServer(("0.0.0.0", 8080), Handler)
+    thread = threading.Thread(target=server.serve_forever, daemon=True)
+    thread.start()
+    register()
+    thread.join()