server: explicit signal handler for SIGINT and SIGTERM (#3595)

When running alone as pid 1 in a container, most signals that would
cause the process to exit by default, are instead ignored by default.
The container runtime will send SIGTERM, wait 10 seconds, then send
SIGKILL, which will work, but moto.server can exit much faster if
it has an explicit SIGTERM handler.

moto/server.py

@@ -4,6 +4,7 @@ import argparse
 import io
 import json
 import re
+import signal
 import sys
 from threading import Lock
 
@@ -245,6 +246,11 @@ def create_backend_app(service):
     return backend_app
 
 
+def signal_handler(signum, frame):
+    print("Received signal %d" % signum)
+    sys.exit(0)
+
+
 def main(argv=sys.argv[1:]):
     parser = argparse.ArgumentParser()
 
@@ -284,6 +290,9 @@ def main(argv=sys.argv[1:]):
 
     args = parser.parse_args(argv)
 
+    signal.signal(signal.SIGINT, signal_handler)
+    signal.signal(signal.SIGTERM, signal_handler)
+
     # Wrap the main application
     main_app = DomainDispatcherApplication(create_backend_app, service=args.service)
     main_app.debug = True